Nash/Rambler 195.6 ci overhead valve six

updated april 2018

you can contact me at it is as if at protonmail dot com

this site is dedicated to compiling information and work i'm doing on the Nash/Rambler 195.6 cubic inch overhead valve six manufactured between 1958 and 1965. in addition to plain old documentation and information my goal is to build modern levels of reliability and power. while this is a very modest design, with the dubious distinction of having no performance parts available for it, other than the factory two-barrel option ("Power Pak") it is proven to be a reliable engine, with forged crankshaft and connecting rods. most of it's shortcomings are easily overcome.

SHORTCUTS TO SPECIFICS

why "195.6"?

Nash engine nomenclature included the decimal, i would guess as part of some long-forgotten "Nash Precision" marketing trope, otherwise, it's sort of annoying. AMC continued it, and that is what appears in service manuals and most internet search results, although enough people call this engine "the 196" to confound searches and identification.

Thanks to Frank Swygert for much information on this engine and for corrections to these pages.

Brief history

This section by Frank Swygert:

Nash's economy L-head six was fitted with an overhead valve head for the 1956 model year. (No L-heads were sold for 1956 or 1957, but it reappeared again in 1958 and was available through the 1965 model year.) The 1956 model of the OHV still had the side mount water pump. The front mount pump came in 57.

The original L-head was a 172.6 designed specifically for the first unit-body Nash, the 1941 Ambassador 600. This increased to 184 inches in 1950 for the Statesman, and the new Nash Rambler got the 172.6. 195.6 came in 1952, again for the Statesman. The Rambler got the 184 in 1953, Hydramatic Ramblers got the 195.6 (small wonder -- the Hydramatic was heavy and took a lot of power!). 1952 was the last year for the 172.6, 1954 last year for the 184. All three engines used the same 3.125" bore, strokes were different (3.75", 4.00", 4.25" respectively). This was unusual since the crank and rods were forged -- the usual practice was to keep the expensive forgings the same and alter the cheaper to change block casting. I guess pennies didn't need to be pinched as much then as after the "merger" with Hudson.

engine summary

here's a rough summary of this engine and it's shortcomings, most of which are dealt with in the sections that follow. if you are going to work on these motors you really need to have a legible copy of the factory technical service manual (TSM). a Haynes or Motors manual is no substitute; those are plain crap. the TSM has detailed information you simply won't find elsewhere. for reference, here are the relevant 1961 TSM engine pages, along with the few 1965 TSM pages pertaining to the differences from the earlier motor.

history

this particular engine has been rebuilt at least three times. twice by me. when this engine was in the 1963 Rambler American 440 Twin Stick hardtop i got in 2005, it had a commercially rebuilt engine in it, .030" overbored. within a year i rebuilt the cylinder head due to sticking valves (old gasoline, foolish mistake).

in 2010 the engine was pulled and received a complete and (what i thought was a) careful rebuild. many of the successful modifications i made to this engine were done at this time. on this site i refer to this as the 2010 build. in 2014 i again removed the engine, did a cosmetic freshen then installed it in the current chassis, my 1961 rambler roadster. in august 2016 i drove the roadster in the LeMons Hell on Wheels '16 Rally, very hard in very hot weather, 8% grades in Death Valley, which did some unpleasant things to the bottom end. when i got home the engine was once again removed, torn down, and this time, after careful diagnosis of it's various shortcomings and problems, completed what i call here the 2017 build, by a professional engine builder, Pete Fleming. that turned out to be a great (if expensive) decision as his machine work appears to be impeccable, finding and fixing problems previous machinists either neglected or couldn't see.

as of this writing (april 2018) the 2017 build is broken in and has 7500+ fairly hard miles on it (after proper break-in of course) -- at a performance level that the 2010 build was not capable of and certainly would not have survived.

21st century warning on buying replacement parts

in the 2010 build of this engine, described below, i bought a combination of new and reconditioned parts from supposedly reputable suppliers, and six years later, after problems resulting in a full teardown and far more careful (and expensive) build, found many of those expensive parts to be severely lacking in quality, and many were not what they claimed to be. specifically:

there were many other small and not so small problems with other parts (wrong gaskets in sets, etc). a lot of this is simply the current historic moment, ancient cars, consolidation of suppliers and parts catalog collapsing.

some of the previously inadequate machine work done in the 2010 build includes the following. the one caveat here is that i simply didn't know a good machinist at the time, and probably couldn't have afforded better work, then. nonetheless some of this was just sloppy. all of these were very specifically addressed in the 2017 build:

many of these problems are my doing or responsibility (learn as you go), mainly my mis-use of modest-cost machine work, and i pushed the engine past it's oiling and cooling ability, etc.

there is simply not a lot of knowledge or lore or performance experience surrounding this engine. i gathered four motors and pulled the head off a deader in a junkyard. none of the cylinders were standard bore, one engine hinted at a two rebuilds (0.060" over). the junkyard head had cracks professionally repaired (nice work here, i saved it, it's work you don't see much any more). one head had cracks in four cylinders, which was dissected to see how the head was constructed and to help place temperature sensors into the head. from this instrumented cylinder head i've gained most of the valve pocket cleanup and cooling system knowledge here.

in 2017 i bought a 195.6 OHV that had been removed from a 1965 American wagon. though the sellers claimed it was "running when removed" most of the pushrods had fallen out (commonly due to re-running an engine after years of storage, valve guides stick). it was otherwise in excellent condition; factory bore ("0 under"), very little cylinder ridge and taper, home marks clear, bearings all good and also 0-under. even the distributor had little wear. from it's numbers it may be a factory replacement block. this engine will hopefully become a source of "factory" data, rare enough on these

cylinder head

performance in this or any engine is limited by the cylinder head, and it should be no surprise that this one-off, interim cylinder head has a lot of limitations. luckily many of them are easily overcome.

the head has a trough intake, adequate short paths, with only one 90 degree turn each from carb to valve. combustion chamber is a popup wedge. the trough has clever Nash anti-reversion wedges that make for excellent fuel distribution.

some of the intake ports are paired/siamesed, some are not. front to rear, the order is I-II-II-I. this confounds port injection fuel-injector layout. throttle body injection will be more than adequate anyway.

it has an interesting advantage in that it delivers perfect mixture distribution to all cylinders, a problem on long inline sixes. if you click on the picture to the right, between cylinders 2 and 3 (and 4 and 5), adjacent to the second head stud from the front of the engine, you will see within the right hand trough wall a ramp-shaped protrusion cast into the trough. It pinches mixture flow at that point -- it is an anti-reversion device, preventing back-flow of intake mixture pulses. All six plugs burn to the exact same color.

the trough is covered with a cast aluminum trough plate, a very handy design for hacking induction. It's flat, easy to fabricate from scratch if necessary.

induction improvements

contrary to popular belief, the trough intake is not a/the major performance-limiting factor. the camshaft is the first limitation, followed by head sealing. the rest of the design and construction is fairly decent.

to gain insight into this head i did a rather involved cylinder head dissection of one severely ruined head. knowledge from that sliced head was very helpful in making this engine reliable.

the valves are adequately sized and reasonably placed. the intake ports, off the trough, are a short, traight shot into each combustion chamber. the exhaust ports seem adequately sized and surprisingly short and only one turn out of the combustion chamber. however the center paired exhaust ports (3 and 4) are routed up to heat the intake trough floor to speed engine warmup. this makes these exhaust ports twice as long as 1-2 and 5-6. see the exhaust port equalization section below for details.

the 2010 build was more or less stock, with minor improvements, consisting of a fair amount of combustion chamber smoothing, deshrouding of the valves, and a Weber 32/36 DGEV carburetor on a carefully blended adapter. the 2017 build, by a professsional engine builder, involved more port work, larger valves, undercut stems, multi-angle valve seats, and a larger Weber 38/38 DGV carb. the 2017 build made night vs. day improvement, and changes since then indicate more induction is still needed. further induction work (and documentation) is ongoing.

Carburetor options

AMC had two carburetor options for this engine: a single-venturi as the base model (Holley 1904, 1906 or 1908 in Americans, or Carter AS or RBS in Classics, depending on year and transmission), and a two-venturi Carter WCD called the "Power Pak" option (relatively uncommon in it's time and now a desirable option). all are very reliable, easy to maintain and un-fussy to adjust and drive, but are lousy performers. for the sort of driving I increasingly do, the WCD annoyingly starved out in every hard turn.

anecdotally, the one-barrel carb "runs out of steam" about 3000 rpm wide open throttle; the WCD will get you about 3500 rpm before it flats out. They are allegedly 200 and 300 cfm flow, respectively, which ought to be enough for more power than that, but wide experience says otherwise.

initially i searched for carb options to bolt onto the two-barrel trough plate; but I soon realized that the dirt-common one-barrel plate with it's standard "YF" bore was far easier to adapt.

The Weber 32/36 DGEV

Redline makes a "Jeep Weber kit" that simply bolts onto the 195.6 OHV's trough plate. the necessary adapter also raises the carb enough to clear the valve cover (which can be removed with the carb installed); if you look closely at the picture to the right, you can see how close the carburetor is to the valve cover.

the 32/36 is adequate for a dead-stock engine, and it's tiny primary bore is a great match for the luggy, low-speed gearing of the stock cars, and the larger secondary provides the flow for heavier loads. overall it flows better and more than the Carter WCD and has none of the jet-starvation issues. it is available new and is easy enough to jet it properly. this, plus an ignition upgrade, would be most of the "low hanging fruit" of low cost performance improvement.

here's the overall relationship of head with the trough plate, adapter and carburetor installed:

Weber 38/38 DGV

the 2017 build required more carburetor, and research showed that the Weber 38/38 ought to be adequate. wow -- never before have i had a single component change make so much improvement in overall performance. however, with this build i had also changed transmission (from two different 3-speeds to a custom T5 and carefully selected axle and tire size) and so RPM range and driving habits changed to match, which also allowed for much more aggressive spark advance. all told the old skinny carburetor was clearly holding it back.

with these positive-feedback-loop changes i've found that the 38/38 is again inadequate; at sustained high speeds (lol, it's all relative, 3200+ RPM at 90+ MPH) the carb is restricting flow and stuck in enrichment. fuel injection is now in the planning stages.

the 38/38 however is a drop-in, bolt-on compatible with the 32/36 and an immediate improvement.

blending the adapter and trough plate

it was easy to blend the adapter to the trough plate and remove all the right angles and sharp edges in the flow. The first thing was to add locating pins to the plate and adapter so that it would stay in alignment after blending . (the adapter has slotted holes that let it slide around.) unfortunately I neglected to take any photos of this, but it's not rocket science. I picked a likely place for two 1/8" pins on the plate where the carb goes and drilled two 1/16" holes about 3/8" deep. into these holes I dropped nipped-off wire brads with the points sticking up above flush approximately 1/32". I carefully aligned the adapter by hand, set it onto the plate (sitting on the brad tips) and whacked it hard with my hand, pricking the bottom of the adapter. I used the prick marks as guides to drill 1/8" holes for the pins, and replaced the brad tips with 1/8" wire. the adapter was to the plate and filed to match.

with the adapter joined to the plate, I smoothed them where i believed the flow would actually go. the big hole in the bottom of the plate had sharp 90-degree edges; I smoothed these as much as I dared, probably a 1" radius. the carb end of the adapter I made slightly (1/32" or so) larger than the carb bore. the inside of the adapter itself was cast lumpy; I smoothed that out substantially, left it with a faintly venturi shape, and increased the overall diameter about 3/16".

throttle linkage

(this mainly applies to stock engine/carb applications.) the throttle linkage worked out neatly. I am very picky about throttle feel, and I truly love AMC's simple system. it allows a feather-light throttle with short travel and great feel. the floor-mounted pedal pushes a bellcrank that rotates a shaft that is coupled directly to the carburetor throttle shaft. Simple!

I retained the original design, and most of the original parts. the Weber's throttle shaft was longitudinally in line already. due to the adapter however it was almost two inches higher.

I found it easiest to cut the firewall-mounted pivot bracket and weld in the two inches of height. (I got it a bit too high, but it's fine.) however, the Weber throttle rotation direction was opposite the stock carb. I made a new pivot rod from an old 232 six pushrod (very handy, those) ground square on one end to fit the slot on the carb; the other end was the correct size for the stock pivot bracket. I welded on a tab for the bellcrank linkage, on the opposite side to accomodate the reverse rotation, and made up the linkage from 10-32 threaded rod and tiny ball ends from my junkbox.

this retains the original look and feel of the factory system, and the mechanical progressive secondary can easily be felt. Sweet!

exhaust ports and manifold

The exhaust side of the 196.6 OHV head isn't too bad. though the hot gases pass through the head for 3" or so, with attendant opportunity to dump heat in the head, the entire path is a straight shot into the manifold, after the usual 90-degree turn in the pocket. the port is sort of rough, but large and rectangular.

the six cylinders exit the head as three port pairs, 1-2, 3-4, and 5-6. 1-2 and 5-6 are identical, a straight shot from the head into a manifold.

the center port however, cylinders 3 and 4, has a huge chamber and odd shape that directs exhaust gas upward, onto the floor of the intake trough, to heat the mixture out of the carb. Overall the center port is twice as long as the other two, if the gases indeed run up to the roof/intake trough floor.

I assume (umm, not really backed up by any facts) that unequal exhaust ports is not helping performance. whatever happens to gas flow in a port cannot be helped by the abrupt U-turn and probable turbulence in the center port. Carb heat is not really an issue in a trough type intake! Seriously, the whole thing is solidly at head coolant temperature. (Though I did actually measure intake charge temperature at speed, it was interesting.)

But it turned out not too hard to make the center port have the exact same size and shape as the other two. The center port casting is very wide, to accomodate all the ducting up and down. I simply (yeah right) fitted 1/4" steel plate sections to box in the port. It really was luck however that the three pieces that comprise the box were able to fit so nicely.

The box sides have to extend deep into the manifold however to reach part of that casting of the same width of the others. This took a bit of tweaking on the bench to allow the manifold to be installed and removed from the head while in the car. It also prevented the use of the usual mounting studs; I substituted stainless steel hex bolts and washers.

The three plate box components were assembled within the port and welded to each other. They were not welded to the head in any way.

Here's the exhaust manifold installed complete, for reference.

Here is the small "good" 1 and 2 or 5 and 6 exhaust port. You can (almost) see that it goes straight in to the exhaust valve pockets. The head is upside-down in this photo (which is how I worked on it on the bench).

Here's the center port. The head is upside-down here also. Note the depth of the U-turn the exhaust port makes up to the intake trough floor; that's a 6 inch rule, the chamber is nearly 2 inches deep. This chamber will be blocked with the roof filler part.

I made heavy use of my sliced up cylinder head in working out these details, which has been very helpful in this project. I'm not sure if these pictures will be illuminating at this point, possibly they will help to refer back to later.

The work started in earnest by cutting cardboard to work up a basic approach. From these I cut rough steel parts.

The roof piece required the most work (recall that the head is upside-down here; the port roof is at the bottom). I trimmed it mostly with a small bench grinder. The innermost end of the roof filler I cocked up a bit with a slight bend, not really visible here. The roof piece is inserted diagonally then dropped into place. The notches in the piece are to fit around bolt-hole bosses.

With the roof more or less fit, the side wall plates were fit. These were easier in the head end of things, as they only had to reach the head bolt bosses. Things were a little tricker in the portion that reached into the manifold; more on this below. Too bad I didn't take more pictures here, it was basically a lot of iterative grind and fit, into the head, then into the manifold (both shown here).

Here are the three pieces before they got welded in place; front and rear. Note the build-up on back, and if you look closely, you can see that the side pieces were Frankensteined, chopped and welded, multiple times for a very close fit. The lumps on the reverse are to position the parts against the head casting.

The final step was to weld the three pieces to each other within the port. My welding isn't pretty, and I don't have a die grinder/Foredom at home, so it went in the car like this. Meh. The port dimensions are now identical all the way from the valve pockets to the manifold.

Here are some other views of the parts and port as installed. From within the valve pocket you can see the roof filler corner. From the outside, the side walls protrude, where the fit inside the manifold.

This is the view from the exhaust pipe end of the manifold. The center port now blends smoothly into the "Y" of the manifold; the two side branches for the other four cylinders come in cleanly from each side.

I made some changes to the manifold itself, mainly removing the choke stove, plugging the holes and keeping the internals smooth and clear. The top choke stove hole got reamed to a taper and fitted with a brass plug swaged into place. I sliced the brass plug flush in place with a hacksaw blade. (The Weber carburetor has an electric choke.)

The bottom choke stove hole got a bolt installed with the head ground funny to fit flush with the manifold walls.



problem: cylinder head thermal issues

run any engine long enough, something will fail first. on this engine, it is the head gasket. Nash/AMC knew there was a problem right from the engine's introduction: the technical service manual specifies a 4000 mile head bolt check/retorque schedule, and with the engine hot. i used to think this was an issue with bolt torque. i am now convinced it has more to do with head bolt motion.

poor thermal coupling between combustion chamber heat and the thermostat seems to be the root cause of a complex stress mechanism. the thermostat is isolated in a pod in the head well forward of #1 cylinder. with the engine "cold" (first operation of the day) block and head are initially the same temperature. when the engine is run, combustion heat accumulates in the cylinder head. since the thermostat is closed, with no coolant flow the thermostat, some four inches forward, remains isolated from combustion heat.

the isolation of the thermstat in it's pod greatly delays the heat signal from reaching the thermostat. the thermostat eventually gets a heat signal, either via simple conduction/convection, or around the thermostat gasket. once the thermostat gets this signal, it opens fully within a few seconds; the problem is that this conduction/convection takes so long that coolant elsewhere in the head is past boiling, with clearly audible steam hammering. when the thermostat does begin to open, very hot coolant in contact with the thermostat causes it to open very rapidly. with this sudden coolant flow the cylinder head coolant temperature plummets, which partially closes the thermostat, causing a thermal undershoot. however with the thermostat now open and coolant flowing, the system begins to warm up normally and within a minute or two stops oscillating.

this thermal cycling is easily measured. i measured coolant temperatures of over 250F, accompanied by audible steam hammering. at the same time that the head is overheated the block remains cool to the touch. i estimate during this time that there is a 150F degree temperature difference between block and head. assuming 150F difference, i calculate 0.024" cylinder head length increase (heating) and decrease (sudden cooling) in these first few minutes. i surmise also that the head gasket is a thermal insulator and "lubricant" between block and head.

given this thermal cycling and expansion/contract it is not hard to visualize the undesirable horizontal motion of the head bolts. when the head grows in length the head bolts splay out in a "V" with the bolt heads moving apart; when the head and block temperatures equalize, they move back to their correct vertical position. i believe this back and forth motion applies rotational torque and backs out the head bolts. the expansion/contraction is likely bad for the sealing surfaces, contributing to leakage. accumulated over time this loosens the head and causes the leaks that are symptomatic of the common end-of-life failures in this engine. if you think this bolt-loosening theory sounds dubious, check out this page at BoltScience.com: the Jost Effect. there's even a video showing transverse motion backing out a bolt!

solution: head sealing

One part of the overall head-sealing fix was the use of ARP brand studs instead of head bolts. Studs are superior to bolts for this application. When a head bolt is torqued, it remains twisted along it's length, due to friction in the threads and under the bolt head. Any transverse motion in the head (caused by thermal cycling...) backs out the bolts. With studs, all of this friction is at the top of the stud, which remains un-twisted. Quality and tolerances are better too.

Since ARP doesn't make a "kit" for this motor and my application isn't particularly stressful on the studs, I simply picked their stock parts from the catalog. There are three different stud lengths. They are coarse threaded at the block end and fine threaded at the top. Twelve-point nuts, machined washers and ARP lube was used. Part numbers are below.

Item ARP part number Quantity Location
Stud, 7/16" x 5.75" AP5.750-1LB 6 Through trough plate
Stud, 7/16" x 5.5" AP5.500-1LB 4 Head ends
Stud, 7/16" x 4.5" AP4.500-1LB 5 Under valve cover
7/16"-20 Nut APN12-1 15  
7/16" ID non-chamfer washer APW1316N 15  
Assembly lube n/a 1 Thread lubricant

assembly

apparently at the factory the bodies were set over the engine and transmission assembly on the line. blocking easy insertion from above is the front welded-in cross-brace, just behind the radiator top tank. mine had long ago been hacksawed out, as is common. with it out of the way top-insertion is relatively easy. i've added a bolt-in internal triangular brace between the inner fenders and firewall to replace it.

i've installed engines without the head attached (2010) and with head and complete transmission (2017). the latter definitely requires that the hoist have a load-shifting trolly.

ARP recommends three torque/release cycles on new studs. for the 2010 assembly, and before operation, I did four, without the headgasket, since that gets a one-time crush. I left the third torque to set overnight. After final assembly with gasket in the car (see the assembly pages for gasket sealing details), I measured stretch on one stud at .012" when torque increased from 20 ft/lbs to the rated 75 ft/lbs. Thanks to David Forbes for the measurement suggestion.

The studs were bottomed in the block and snugged up with an allen key two-finger tight, assembled with ARP hardware and lube and torqued in three stages to the rated 75 ft/lbs. I did not start it until the next day.

these same studs were used in 2017, and the builder used his own method of assembly.

retorquing

(this applies only to my first 2010 assembly.) retorquing ARP studs is utterly different from working with stock head bolts. I used ARP's special moly bolt lube and the difference was night vs. day. When re-torquing, there is no typical "sticktion", no need to crack the nuts loose before torquing; they simply turn, then stop. Part of this is simply that the clamping friction is in the nut, at the top of the stud, and not a twisted bolt deep in the block.

The head studs have been retorqued three times since first assembly. The first re-torque followed the first full operating temperature run in the driveway to set valves, initial carb and spark settings, after an overnight cool down.

Upon every retorque each nut rotated the exact same amount. This was good, because two end nuts will not accept a socket when the rocker shaft is installed; I used a box-end wrench and extender and turned them the same rotational angle as the rest did with the torque wrench. (And as far as I can tell, no one makes a 12-point box end crows foot socket.)

The third retorque, at 1000 miles, zero rotation. It appears that stud stretch and headgasket crush is complete. I will continue to check it at intervals, but hopefully the need for constant retorquing is over.

Here are some pics of the studs installed in the lab. this is the 2010 build.

The stock head bolts penetrate the block exactly one inch. Placement isn't that great, even to my novice eye; some are along casting side walls, and some are in the middle of horizontal spans. Headbolt spacing is wildly uneven, but there's nothing to be done about that. Here are pics of the stock bolts and their protrusion through a section of a junk head:

solution: cold-engine startup thermal spike

in contrast to the seriousness of the thermal design flaw described above, the fix is almost laughably simple: drill a bypass hole in the body of the thermostat, install the thermostat with the hole towards the front, so that it "leaks" coolant past the sensor button. hole-drilling is often done to allow purging air bubbles from the system. many aftermarket thermostats come with a drilled hole and a loose pin so that crud can't block it. i suggest a fairly large hole, eg. 3/16". this slows the infamous "fast warmup" this engine is known for; while inconvenient for cold winter mornings better temperature regulation will have only positive effects. i suspect that many thermostat installations leak slightly, by design or by accident. this might explain the disparity in experiences (some have head failures, many don't). i suspect engines with constant if small coolant flow do not have this thermal-spike issue. my engine obviously had it; and i used a new thermostat that appeared to close completely, it had no hole, and carefully assembled by me with Right Stuff.

anecdotal research seems to make sense of why some engines fail and some don't: some thermostats already have a bleed hole, and some thermostats or thermostat installations leak or flow a small amount of coolant. if warmup "signal" reaches the thermostat button via any mechanism, the system works fine.

problem: inadequate cooling system

this engine was introduced in 1941 as a 75 hp flathead. AMC installed an inadequately designed overhead valve head on it in 1958, and with "Power Pak" brought power up to a claimed 138 hp, and "modern" highways put additional burden on the cooling system.

cooling system inadequacies and design flaws are easily fixed.

solution: bigger/better radiator

easy for me to say, i don't care about "stock". Speedway Motors' "Ford type" generic aluminum radiator has twice the cooling at half the cost of repair or replacement. the downside is that you need to fabricate brackets to mount it. i estimate my 18" x 24" two-row radiator has two or three times the capacity of stock, at half the cost. i get a routine 60F temperature drop inlet to outlet at highway speeds. my SPAL 16" 1500 CFM fan is adequate, just. the fan is needed only under 10 MPH even in Los Angeles summer weather; 10 MPH generates far more than the alleged 1500 cubic feet of air.

the water pump is increasingly a problem. though adequate, they are hard to find. there are at least three different variations, two of which have different shaft lengths.

crankcase ventilation

it seems "well known" and routinely accepted that this old engine consumes a lot of lubricating oil. however it seems that most of the oil consumption may be due to aerosolized oil within the crankcase, drawn through the PCV system or out the road draft tube.

i wish i had paid attention to oil scraping and pan baffling when i last had the engine apart.

crankcase ventilation in most model years of this engine was done via a road draft tube, a lage diameter (2") tube open to the road and pointing downward to generate a (very) faint draft, drawing air in through the oil filler cap and screens in the valve cover. PCV was introduced, and by it's final year in 1965 it had evolved in a number of ways, mainly closing off the various screened vents in the valve cover and filler cap. in all guises the system seems to suck a lot of oil into the intake. (to be fair, i run mine unreasonably hard and fast.) the block is tall, the rods are long, and the camshaft is partially splash lubricated. one of the old flat-head side covers, still present in the OHV motor, had a baffle added and is where the PCV system draws from, and i and many other can attest to it being a source of liquid oil in the intake.

my current scheme, shown below, seems to have reduced PCV oil consumption to near zero. though it looks like a "catch can" it is better considered in terms of volumetric flow rate; the can is a great widening of the PCV hose. for a given flow volume of gas, the velocity depends on the diameter of the "hose", and the can is a very wide hose. the can is loosely filled with coarse bronze wool to condense the slow-moving oil mist back into a liquid, which runs back into the crankcase via the lower hose, similiar to how old building steam radiator heating systems work.

the small can seems adequate. the size of the lower hose matters; here it is 1/2", which allows liquid oil to drain back while mist flows upward. the PCV valve is stuck in the grommet on top, plumbed to manifold vacuum via a 3/8" hose. the small hose stays dry, while the bottom hose is wet with oil. so far so good. a recent trip at sustained high speeds (2500 - 3500 rpm for approximately 1500 miles) reduced oil consumption to zero.

the engine block

nash/amc/rambler did not serial-number chassis and engine, and continuously made many small and occasionally large engineering changes, often with no change in part number or casting number. as per the rest of the industry at that time car and engine options and features came and went and were forgotten (E-Stick clutch, various incarnations of "heavy duty", ...), repair shops swapped and modified parts seemingly without reason to keep cars on the road, and for a car that was apparently unloved, it is rare to find one with it's engine not overbored. all of this combines to make precise parts identification difficult. luckily, it doesn't matter, all blocks and most parts interchange with only minor warnings and issues.

the block is fairly ordinary cast iron. four main bearings, siamesed cylinders (eg. no water jacket between paired cylinder walls). the block retains the old side valve adjustment access covers but there's nothing behind them but pushrod side view. the headbolt pattern sucks. some of the headbolts draw up from vertical walls and some from horizontal webbing. the bolt pattern and other block deck issues make for head sealing issues.

the camshaft is in the typical pushrod OHV configuration, driven by the usual chain and sprockets under a cover on the front of block. harmonic balancer is external with pulley groove. fuel pump is driven off a camshaft lobe. mushroom cam followers install from bottom, requiring engine removal for access. the cam follower's very small diameter limits cam profile regrinding, as does its very small base circle. the typical helical gear on the camshaft drives both oil pump and distributor, but each has it's own shaft and driven gear (specifically the distributor does not drive the oil pump.) all OHV blocks are drilled for the flathead's distributor location on the right side of the engine, filled with a welch plug.

there are a few variations in the casting itself, mainly variations of oiling schemes. all of the pre-1964 engines have the small external oil pump with optional partial-flow filtration, fed by a 3/16" steel line off the main gallery into the filter located up top/front of the engine, and drained back into the pan on the drivers side. 64-up engines used in the new 01 (American) chassis have an oil pump with integral full-flow oil filter. the full-flow pump and filter will not fit into the tight confines of the earlier 01 chassis.

the rocker shaft on the cylinder head is lubricated by an external 3/16" steel line also fed from the main gallery, into a hole in the head that feeds the front shaft pedestal. in the earliest years this received full flow directly off the main gallery. around 1960? the valve train feed was from a new casting boss off the camshaft front journal just above the main gallery. the camshaft itself was modified; the front journal had a flat that with each rotation allowed a squirt of oil of approximately 30% of the cam's rotation, to limit total oil to the head.

cranckcase ventilation was a simple road draft tube in the early years, PCV first in california then national. the draft source (road or PCV) draws from front valve/pushrod access side cover. air taken in via the long crankcase oil filler tube dipstick vented cap, and many engines have stamped vents in the valve cover, depending on year and carburetor model.

valves and camshaft

the cam and valve setup is an ordinary camshaft in block, solid followers, pushrods, rockers on a shaft, 1.5:1 ratio. valves in head. valve seats are cut into the head casting. valve tappet clearance adjustment via threaded pushrod socket. the OHV block retains the old flathead side valve adjustment access cover, whose main purpose in the OHV engine is to leak oil, and a few different variations of crankcase ventilation outlet.

the camshaft, and followers, are probably the major performance-limiting feature of the engine. there are cam blanks to be custom ground, and the single OEM cam has it's base circle very close to the rough casting; further the short lift, short duration lobes leave no meat for regrind. lobe acceleration and absolute lift are further limited by the tiny mushroom tappets, which rock faintly in their sockets.

there is barely enough metal to grind a slightly "RV"-ish lobe with a little more duration and no more lift.

note however that the L-head engine has an identical camshaft, with substantially more lift (since there is no lift-multiplying rockers). therefore the flathead camshaft may make for a good "blank" to regrind. i did not realize this in time for my current engine.

note also that the flathead camshaft will not have the top-end oil modulating flat on it's front journal.

crankshaft, connecting rods, pistons

the crankshaft and connecting rods are all forged parts, with very large and nearly overlapping journals. though only four main bearings the bottom end seems more than adequate. be careful selecting or mixing connecting rods; i have found at least two different parts, fully interchangable, with identical part and casting numbers, that were over 100 grams different mass but within each set, 10's of grams difference. more old world engineering. (the difference seemed to be at the little end.) the pistons are heavy, with thin rings, cast aluminum with steel inserts, of a popup wedge design. aftermarket pistons are often of terrible quality. most of the engines i've disassembled for parts were .030" or .040" over, with one .060" over. the blocks can apparently be bored .080" over without problem.

for my 2010 build i got decent quality replacement pistons and rings from Kanter. i static balanced those with a gram scale, and they were not bad to begin with. rods and bearings were fine, probably; though connecting rod bearings failed (leading to the 2017 teardown) it seems fairly likely that the failure was due to the collapsed (softened) oil pump pressure relif sprign i bought from Kanter.

lubrication system

the stock oil pump is an external but typical gear pump. the pump inserts into the lower side of the block left, pulls oil from the pan and pushes directly into the main gallery. top end (rocker shaft, etc) is lubricated by an external line that carries oil from a tap on the block, up to the head casting where it flows upward through a rocker shaft support, into the hollow shaft and from there to each rocker. on earlier engines the top-end source is the main gallery, eg. full engine oil supply. on later engines the top end is fed by an intermittent source generated by a flat on the camshaft's front journal that pulses the main gallery feed, to limit oil flow to the top end.

oil filtration was essentially bypass filtration, which apparently works better than you'd think, with running engine oil turnover rate. when an oil filter is present (it was an option in early engines), there is a "tee" bypass in the cylinder head feed line that then feeds both top end and filter. the filter output, via 3/16" steel line, is to the crankcase on the right side of the engine, behind the generator location low on the block.

crankshaft main journals (4) are fed directly from the main gallery as is each cam bearing. connecting rod bearings receive oil via drilled crank. the connecting rod big end has a squirt hole that lubricates the cam journals. the cam is also splash lubricated. some years have piston squirt lubrication via conn rod squirt hole. the specifics of the oiling system make it very easy to modify.

with quality parts in good condition, more difficult to acheive than you'd think, the lubrication system seems more than adequate for higher performance. however, oil heating is a fairly severe problem; see below.

full-flow oil filtration and cooling

i modified the pump for full-flow filtration by fabricating a new pump top cover with pressurized oil outlet and blocking the outlet on the bottom of the pump body with a steel gasket that blocked the factory oil outlet hole that fed the main gallery. with this mod oil is pumped out the cover, through a PTFE 6AN line to the rather large oil cooler mounted in the front valance, from there into the oil filter, the filter outlet feeding the main gallery.

In 1964 AMC did add a full-flow filtration oil pump to this engine, but it won't fit into the pre-1964 small (01) chassis, the filter doesn't clear the suspension. I got a rusted pump from a friend, it was too far gone to use but it served as a model for cogitating on a solution. The fundamental limitation in the pre-1964 American chassis is clearance. The oil pump is external to the block, and sits very close to the lower A-arm pivots. I believe that if I had a decent Classic pump I could have modified it for my own ends, but I couldn't find one, and the non-filter pump is common enough so I based my hack on that.

overview

Here are some pictures of the completed system with the engine out of the car. The chosen oil filter location is very convenient for many reasons, including under-car access, hose length and mounting point stiffness. (it also worked out well when the oil cooler was added in 2017.)

(the initial build in 2010 was with the rubber hoses shown, which were replaced within a couple months with the 6AN braided stainless steel, PTFE lined hose shown above. the "red" engine is the current 2017 build, the green engine is the 2010 build of the same engine. i didn't trust the hose barb system.)

the oil cooler is not yet shown here.

The pump, of the common gear type, (green assembly with three cover bolts, lower left in the first picture) sucks oil from the pan and in this modified system, pushes it out the pump cover through the brass fitting and lower-most hose, into the filter inlet. Oil flows through the filter and out the top-most hose (arches up and over) and into the center of the main gallery where the AMC factory conveniently put a 1/4" NPT tapped hole, directly above the original pump feed location.

Pump body modifications

The trick was to interrupt this circuit to insert the filter. This turned out to be very easy. My first version involved drilling and tapping the pump body outlet for a plug but my final version was vastly simpler -- leave the pump untouched and replace the paper gasket with a 20-gauge steel plate "gasket" the exact size and shape as the pump-to-block gasket that didn't have the outlet hole cut. I used Permatex Right Stuff as sealant. There's a lot of leeway in pump to block insertion depth (gear mesh depth) and during normal operation there's no or little pressure difference on each side, so it can be thin.

I then fabricated a new cover for the pump with an outlet directly opposite the original outlet in the pump body; oil under pressure now exits through the cover. The cover is fabricated from two pieces of 1/4" steel stock, the small piece stiffens and builds up height for sufficient threads in the fitting, and allowed the driven-gear lubrication well to be a simple through hole in the larger plate. The small milled groove feeds pump inlet oil (not outlet pressure) to the top of the driven gear and exactly matches the factory configuration.

The location of the new pump outlet hole was fairly touchy; note that it is not centered in the gear output cavity, but slightly to one side. This is due to interference with the top pump bolt. socket-head bolts are required. The hole seems large but the effective diameter is actually the ID of the fitting, about 3/8".

After welding, the plate warps; I milled it more or less flat then ground it flat flat with 80-grit wet-or-dry on a ground cast iron plate. Flatness matters here, this is the mating/sealing surface for the pump gears as well as the pump body gasket surface. The gasket is dimensionally thin, hard, and subject to full pump pressure, and this is a core mission-critical part. It's worth the extra effort to get this perfect. Note also that the gasket is trimmed around the new outlet hole.

To the cover I added a 90-degree 3/8" pipe to 1/2" flare tubing adapter. I used a stainless steel part instead of plumbing store brass. i needed to shave about 1/16" off one side of the flare adapter to clear the hex socket bolt head. I assembled the adapter and plate on the bench and was able to get it very tight. It should be left pointing towards the front of the car, up 45 degrees or so from horizontal; this gives maximum clearance under the car and allows for easy wrench access.

Note also that internally, the fitting must be flush or below cover plate flush; I pre-assembled the cover plate and fitting, then filed the fitting (not while installed in the cover!) such that it was 10 or so thousandths below flush when assembled.

the hex head bolts shown in this early photo interefered with the line fitting; I replaced all the bolts with socket head bolts. The top bolt also needs to be 3" long rather than the stock 2.5" given the additional thickness.

plumbing, oil filter, sizing and flow

This system puts full un-bypassed pump pressure into the inlet of the filter; the pressure relief bypass is downstream of the filter. This is fine as long as the upstream flow restrictions are low, which they are. I chose a filter (initially Wix 1374, recently switched to Wix 51088) that has both anti-drainback and a 10psi internal bypass; when the filter inlet pressure exceeds filter outlet pressure by that much, it lifts off it's seat and bypasses the filter. The stock oil pressure relief valve remains in the stock block location and does it's job from there.

since the filter is mounted upside down, the anti-drainback feature isn't needed.

I was wary of putting flow restrictions into the main oiling system. The factory passage from pump to main gallery is only 5/16" diameter, but it's only one inch long! Here I am adding nearly 24" (60" with the cooler) of additional path and filter. The fitting out of the pump is necessarily a 90-degree bend but all of the others are be straight.

Ever wary of reliability problems, this new system leaves increased exposure for potential failure: hose-related failures and problems with the filter. a plugged filter isn't a problem on a car well maintained.

oil pump "blueprinting"

This oil pump is very old technology. Huge clearances, rough castings, heavy, cheap to make, and reliable. Note the rough casting in the pump outlet! There's a lot of room for improvement here...

My first oil pump failed. Live and learn.

Stock gear-end clearances on the stock pump run about .008 - .009". Hoping to improve oiling, I carefully ground the pump body down so that total gear-to-cover clearance was about .002". Oil volume and pressure went way way up -- 40+ psi at idle, 60 - 80 psi above 1500 rpm. In fact I had problems with the bypass valve not able to dump enough oil back into the pan to keep cold-engine pressures under control. 2000 miles later, the driven gear welded itself to the cover, shearing teeth off the drive gear. (I shut the engine down immediately, it seems no further harm done.)

I now have a dead-stock oil pump in place, with the blocking plate and custom cover and full flow filtration. Pressures are a more normal 20+ psi at idle, 40 - 60 psi hot 1500 rpm and up. Somewhere between these two extremes, .002" excessively tight, .009" factory loose, is probably a happy compromise. Without a specific reason I'm reluctant to do the experiments. Probably dropping clearances to .005 - .006" would make for a healthy increase without any reliabity threat.

note the pump packed with vaseline for initial startup -- this is flatly required. it is not possible to prime the pump externally. it is geared directly to the camshaft, not via the distributor drive gear. it's a slight pain to pack but keep the gasket surface grease-free so that sealer will seal, but this is a critical feature.

2010's modded pump disassembled in 2017

when the engine was again overhauled in 2016/2017 this modded pump had been in use for six years and some 50,000 miles. there is some minor scuffing of the cover by the gears. i neglected to photograph the steel blocking gasket.

i did not re-use this pump body and gears; it was used when i started, and by sheer luck a found a brand-new Melling M61 pump to replace it. it received the same modifications and fabricated top cover and is now in service. gear to body clearance is tighter too.

Drawings and dimensions

oil pump pressure relief valve spring

oil pump cover gasket

probably the major contributor to the 2010 engine's failure in 2016 was the oil pump pressure relief valve spring, which i had purchased new from Kanter in 2010. some time during the 2016 LeMons Hell on Wheels Rally it collapsed, and fairly suddenly. new replacements are scarce; i bought one at a dear cost from Blaser's AMC. it's dimensions are below, which should be sufficient to source a replacement from industrial sources. (the shorter spring in the pic is the dead one.) in my experimentation before this new spring arrived, i experimented with shimming the old spring. this actually worked well, and since it can be done from outside the engine, is easy to do. shimming would be acceptable to get a new generic replacement to the right output pressure. it's likely not OK for a used spring that's lost it's temper, except in an emergency.

AMC oil pump pressure relief valve spring, part 3112400
length 2-5/8"
diameter 7/16"
wire diameter 0.058"
turns 22.3

note that i have found used springs with different number of turns. i did not measure overall length beause they were all 50 years old and i didn't trust that dimension.

oil pump solutions, examined but not followed

Below are some pics of the 1965 full-flow filtration pump I got from Joe. Though the casting was too pitted to be used, I did make mods to it that would have solved the problem.

This casting is based upon the venerable old pump, but has a complicated cover that incorporates the overpressure bypass that dumps oil back to the pump inlet; therefore the filter will never get unregulated pressure. That's a required choice for an OEM environment, but not a much of a worry in mine.

Worse, this pump does not fit the earlier blocks; the block casting is wider at the pump mounting face, because there is a passageway in the pump outlet that requires the block face to seal it. The old blocks have air where the new block has cast iron.

However, I needed to block that outlet anyways, so I fabricated a steel button that would clamp under the pump body and block the main gallery passageway. Additionally, the pump outlet would be drilled and tapped as is the other pump. This made the button dimensions critical (note the paint marks I used to verify alignment and contact area) and in the end I abandoned this path; the other pump is far easier to mod, far more common and is in fact lower-profile than the 1965 pump.

problem: lubricating oil overheat

a major part of the 2010 build was to modify the oil pump for full-flow oil filtration. after the failure of the 2010 build (on an admittedly abusive rally) i finally thought to stick a temperature sensor in the main oil gallery. on a quite modest 20-mile Los Angeles freeway run, 65 MPH in 75 F weather, engine oil temperature rose to 230 degrees F. though 230 F isn't itself a problem, that it did so on such an easy drive in 2017 points out the demands we make today on old iron. there were no freeways when this engine was new.

solution: external oil cooler

as part of the 2017 build i added a 10" x 10", stacked plate cooler with fan and with that, 70 MPH all day cruising temperatures are in the 200 F range. to do so on this engine requires the full-flow-filtration modification mentioned above. there is simply not enough oil flow through the stock bypass filtration (with it's 3/16" steel line) to remove any real heat.

other minor lubrication fixes and improvements

the valve cover design is pretty good but engine oil flows along the rocker shaft and pours steadily right onto the spot where the cover gasket meets the head, and often develop a seep there, even with a new gasket. any tendency to leak is made worse by the oil dripping off the rocker shaft, onto the back edge of the seal.

a simple twist of steel baling wire around the far end of the rocker shaft provides a path for oil to return to the cavity in the head casting. there is now no oil leak or mess even when running with the valve cover off. the same wire twist has been in place for six years. it is tight enough to have a shape, but loose enough that it could never wedge itself between the rocker and washer. Even if it wears into two pieces they'll lay harmlessly on top of the head. here's a brief movie (AVI format) of it in operation.

ignition and spark advance

the factory stuck an application-specific Delco Remy distributor and coil and points, mechanical and vacuum advance, on the passenger side of the engine. the distributor is extremely spark-advance-limited, 11 degrees maximum mechanical advance. no other distributors known to "fit in the hole". the L-head version of the engine uses an incompatible Autolite distributor inserted into the drivers side of the block. the hole for this is still present, filled with a plug, i suppose with some effort you could run two distributors just for perversity.

a Pertronix module will solve the limitations of points, but my testing has shown that wear in the distributor itself (since new ones are not available), which shows up as timing jitter and weak spark, combined with the utter lack of total spark advance (some 22 degrees), is a major performance limiting factor. consider also that insufficient spark timing adds a lot of heat to the cooling and exhaust systems.

however there are mods and improvements you can make to the stock distributor that are fairly easy and worthwhile if you intend to keep it in place.

Improving the old Delco Remy distributor

The first order of business is to pitch the points. You can't even buy good ones any more, the aftermarket parts are all crap. While the speed this engine turns (red line is 4500 rpm) isn't pushing things a Pertronix Ignitor, part #1162A, ("Delco 6 cyl with vacuum advance") and the matching epoxy coil is substantially hotter, and more reliable, spark without being wasteful (and arcover-inducing) overkill. (One annoyance with the Pertronix is that you have to file a small clearance notch in the cap to clear the two wires that now come out; if I had thought ahead I would have looked at drilling the distributor body.)

  Stock Modified
Static 5 13
Centrifugal 11 20
TOTAL 16 33
(Vacuum advance) 11 11 - 16 (see text)
(Vacuum source) manifold manifold

Mechanical advance

Mechanical advance on these old Delcos is limited by a pin on the points-cam assembly that lives in a hole on the main shaft assembly. The pin is small, the hole large, so the hole limits rotation to 11 degrees. Enlarging the hole is obvious, but too much and the fly weights will hit the housing. Enlarging the hole is obvious, but total advance change is limited by the weights hitting the distributor case in the outward direction, and the weights hitting each other in the retard direction.

I drilled the hole out to 33/64s (the parts are all hardened, but I happen to have a carbide-tipped bit that size) and sparingly ground the tips of the weights such that they would fold in closer. I stuck some random soft springs from who-knows-what distributor curve kit, which got the advance to come all-in around 2000 rpm, about right for this motor.

Optimum static timing is somewhere around 10 - 16 degrees BTDC, for a total of 32 degrees. It still never pings. It could use more. I did some before and after 0 - 60mph tests which were inconclusive. Mileage has been steadily creeping up with no carb changes, so that's all good.

If you need to do this to another random distributor, watch for the weights hitting the housing; that's the advance limit. I got a few more degrees out of it by grinding the tips from the weights that allowed them to fall all the way back against the cam; stock, the weight tips touched.

Here is maximum and minimum spark advance (minus springs and retainer). Max is limited by the hole (see below) and minumum by the weights hitting each other. Under the rotating assembly you can see the pin and hole that limits advance travel.

Here's the hack. It's not a big deal. A hole drilled, and weight tips ground and checked, repeated until the weights laid flat on the cam. Removed about 1/16" at the tips where indicated.

Vacuum advance

Hint: when you are fiddling ignition timing, drive around with the vacuum advance hose removed and plugged. Vacuum advance is for part-throttle (high vacuum) cruise only, and doesn't affect power, but will affect drivability or pinging when it's wrong, and it complicates things. Mileage will drop but it greatly eases making adjustments -- one variable at a time.

It turns out, you can easily get 16 degrees vacuum advance by filing the limit-stop down (see below) but don't bother -- once you've upped overall advance, the engine will not tolerate a lot of part-throttle advance. Stock is fine here.

a better ignition solution: EDIS-6 and MegaJolt Lite Junior

If you aren't familiar with EDIS, you will need to research that yourself; a good place to start is the MegaSquirt page. It's a great system, and has been adapted to lots of orphan cars. It puts out as much spark power as many high-performance aftermarket ignition systems, for a fraction of the cost. And for old or odd cars, you get to ditch worn out, hard to replace and frustrating distributors. The MegaJolt Lite Junior controller is designed specifically to manage EDIS for enthusiast installations. RTFM.

The Ford EDIS ignition is easy to adapt. The hardest part is the trigger wheel mounting, but a simple adapter lets you bolt one onto the harmonic balancer.

I bought a "kit" of EDIS parts from Boost Engineering if you are less lazy than me you can scrounge 'em from a junkyard or pick from eBay. I got a coil pack, 36-1 wheel, sensor, wires, all in one batch. Clean and tested good, and still in use 7 years later.

EDIS needs a computer to manage it. (By itself it will run the car though, in "limp home" mode, fixed at 10 degrees advance; very nice if your computer dies! Relaibility matters.) That is what the MegaJolt Lite Junior does. Nice little box, buy as a kit or built from various vendors, and the single biggest expense of the project. See AutoSports Labs for details and installation instructions.

Trigger wheel and sensor install

The hardest part of the job on this engine is mounting the sensor and 36-1 wheel. When I rebuilt the engine, i fabbed up a nice clean stiff mount for the sensor and welded it onto the timing chain cover. It would not be all that hard to work up another solution with the engine in-car, probably from below. it's a little tight in there, as you can see from the photos (the one on the right was taken from below).

The mount for the sensor (pickup) is simple and easy, with the timing cover off the engine:

here's the 36-1 ring to harmonic damper adapter. Ignore my shitty welding.

Mounting

I chopped the mounting ears off the provided bracket, welded up new ones to mount it to the inner fender and accept the EDIS6 module, to create an ignition module I could wire up on my bench.

The end result was a neat package with four wires to pierce the firewall, and a short cable that runs to the pickup.




Pay a lot of attention to grounds and shielding! The signal from the pickup is weak, and susceptible to noise picked up in the wiring. The MJLJ documentation is fairly clear here, but I as always go for overkill. All of the grounds -- coil ground, EDIS module ground, and MJLJ module ground -- were short heavy wires, twisted and soldered, with crimped lugs soldered, and screwed to the inner fender in one spot. A #14 wire was run from there through the firewall for the MJLJ box -- do not ground it "conveniently" under the dash. I extended the pickup shielding up to the EDIS module connector using aluminum foil -- it looks rough in the picture above (I wrapped #22 uninsulated wire around it for an electrical connection, then 3M electrical tape for mechanical strength). Overkill for sure, but I've mounted the module very close to the spark coils, there's a lot of energy in the air there. Easy to do now and avoids trouble on the road!




The wires that came from Boost Engineering are crazy long, and loop all over the place. I've ordered a set of replacement MSD spark plug boots from Summit, I'll shorten them up, that will tidy up this mess. The distributor hole plug was simple, just a flat piece of cold-rolled stock cut to fit and silicone sealed.

The sensor to 36-1 wheel gap worked out to be .045".

Drilled a 9/16" hole in the firewall for the harness, mounted the MJLJ box under the glove box. Wired up everything but left the SAW signal (MJLJ control signal to the EDIS controller) disconnected so that EDIS would run in stand-alone "limp home" mode. Much easier to test one thing at a time.

Firing order

The firing order for all Rambler and AMC sixes is 1-5-3-6-2-4, clockwise crank rotation, counterclockwise distributor rotation. The EDIS coil pack is marked, but it's for the wrong engine; ignore it. The proper wire order for all AMC sixes (1950 - 1989) is below, but working it out from first principles is easy.

Inline sixes have three pairs of cylinders. Each pair of pistons is 120 degrees apart on the crank, and is in the same physical position in the cylinder, but each in the pair is two strokes apart through an Otto Cycle; eg. one on Compression while one on Exhaust.

It's easy to determine which cylinders fire when: for an overall order of 1-5-3-6-2-4, the pairs are: 1 & 6, 5 & 2, 3 & 4. Look at the top of the distributor cap: note that starting with #1, 6 is directly opposite 1. Next is 5; 2 is opposite 5. Next is 3; 4 is opposite 3. Those pairs are the ones with the pistons at the same position in the cylinder.

EDIS takes advantage of this physical pairing. By firing both cylinders in a pair simultaneously, it doesn't need to know camshaft position, only crank position; when the pair approach TDC one of them is in compression stroke, so sparking both lights it off without knowing which. The other spark is "wasted". This vastly simplifies the ignition, and triples the time to saturate a spark coil, each coil is smaller, lighter, runs cooler. Win win win.

Wasted-spark lets you re-think what firing order even means. Because it fires each cylinder twice in an Otto Cycle -- compression and exhaust -- the firing order is really just three pairs, not six individual cylinders. EDIS 6 coil packs are marked A, B, C. EDIS fires them in this order: A, C, B.

AMC six EDIS firing order
cyls... coil
1 + 6 A
5 + 2 C
3 + 4 B

Six cylinders, but only three engine revolutions, a coil firing every 120 degrees. It doesn't matter which terminal of the coil you wire a cylinder of a pair to! As long as cylinders 1 and 6 go to coil A, etc, it works. Electrically it doesn't matter, but under the hood it means you can attach plug wires so that they're neat and don't cross.

Initial checkout

Once wired up as a module and installed, there are four wires that go through the firewall (+12V switched, ground for the MJLJ, and PIP and SAW in a shielded cable), and the sensor cable. That's it! The engine started and idled first time. If it backfires, you may have the firing order wrong, or the trigger wheel positioned badly (the MJLJ installations are pretty clear). If it doesn't fire at all, you may have the sensor wired backwards (swap the wires) or the sensor is too far from the trigger wheel.

Configuring the MegaJolt Lite Junior

It goes as the MegaJolt documentation says. I am very comfortable with computers, but I deeply want to keep computers out of my old cars... but it sure is nice to have precision ignition timing! And tuning the MegaJolt is easy, there's just not that many variables or complexity.

Laptop, Keyspan serial/USB adapter, and the MegaJolt configurator program downloaded from their site. Easy enough. I created a spark map by the seat of my pants -- well not really i know how my distributor is curved from spending so much time with it (and taking notes...)

The first thing I did was to change lobal stuff (number of cylinders, normally aspirated), and the axes of the map -- the default is 500 to 9500 rpm (YEAH RIGHT!) and load 10 - 230 (1 atmosphere boost). I changed rpm to 500 - 5000 in 500 increments and "load" 10 - 100 (103KpA is atmospheric pressure, eg. zero vacuum).

Second I verified that the sensor and 36-1 wheel are aligned right -- i entered 0 in the lower two high-load spark map boxes, uploaded it, and with a timing light looked at the timing marks. My system was off 2 degrees. There's "timing mark" global setting. Nice!


Creating a custom timing map

Now to make the initial map. I started with what I know as good starting points for the four corners of the map. These are numbers you will be familiar with if you're comfortable tuning your engine now.

The first thing to set is the load=100 horizontal row of values -- this is pure mechanical advance, eg. a distributor with the hose pulled off. Mine, 500 rpm is 10 degrees advance (static setting), 2500-5000 rpm is full advance (22 degrees, what my hacked distro did). I simply interpolated values by eye, 1000 - 2000. Somewhere, I actually measured this with a hand vacuum pump and a timing light, I'll pull out my notes sometime and look at it, but i recall it being more or less linear.

The far "corner" of the map -- high rpm, low load (high vacuum) -- that's total mechanical advance (static 10 + 22) plus full vacuum advance (11) or 44, 2500-5000 rpm gets that value.(That's a hypothetical, it's unlikely you'll run it > 2500 rpm at high vacuum; in fact I entered lower numbers 3000+).

The other "corner" -- idle, high vacuum -- where a distributor you're always fiddling with "ported vacuum" vs. manifold vacuum you get to actually set it directly, no more compromises. Often, full vacuum is too much, and no vacuum too little. Initial experiments determined that 18 degrees total advance "seems nice" (utterly unscientific, but a starting point).

From there I simply eyeball-interpolated the center of the table; the low-load runs from 18 degrees advance (500 rpm) to 33 degrees (2500-5000 rpm). from that basis on-the-road tuning ended up at this in 2012:

in it's current (april 2018) state of tune, with T5 transmission and 38/38 DGV carburetor, much more aggressive spark timing is needed: