Rambler 195.6 OHV block

updated 14 mar 2020

the engine block

nash/amc/rambler did not serial-number chassis and engine, and continuously made small and occasionally large engineering changes, often without changing the part or casting number. as per industral standards of the time options and features came and went and were forgotten (E-Stick clutch, various incarnations of "heavy duty", ...). repair shops swapped and modified parts to keep customers cars on the road, and for a car brand allegedly unloved by the public, it is rare to find one with it's engine not rebuilt and 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.

all 195.6 engines are very short, with only four main bearings. cylinders are siamesed pairs (no water jacket at the inside where cylinder pairs join) leaving a very narrow block deck surface that challenges head gasket sealing and requires care in block deack and head machining (careful flycutting, not sanding).

the block retains the old flathead 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 block deck issues make for head sealing issues.

the camshaft is the typical pushrod configuration, driven by the 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 top-end 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 draining back into the pan on the drivers side. 64-up engines 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.

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 fair 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.

be warned that there are also two different ring thicknesses used in different years. check before replacing.

avoid resurfaced tappets

for my 2010 build i bought used but resurfaced tappets. this turned out to be a mistake, as the resurfacing apparently removed all of the hardened surface of the mushroom head, precisely where it is most critical. the working face of all 12 tappets was severely pitted, while the matching cam lobe was essentially fine.

the cam lobes were fine, no scoring. you can see one lobe of the cam that came out of the engine, with these lifters, in the background of the first photo. this was not an oiling issue, but metallurgy. don't use resurface tappets.

for the 2017 build i bought new, NOS, tappets from Kanters. they have a faint crown. the mushroom head is black oxide, as is the pushrod ball socket. overall length of the NOS tappets is 1.878", i measured 6 of the old ones, all were shorter at 1.864" in height. this implies that the resurfaced parts had .014" removed, assuming all tappets are initially the same height.

there's a discernable (thumbnail) wear pattern on the cylindrical section, up under the mushroom. this appears to me to be the lateral force caused by the cam thrusting the follower sideways during normal operation; that's a feature of the mushroom design (and why AMC and everyone else ditched them). as the cam operates, the lobe wipes the tappet crown, slightly off-center, rotates the tappet presumably to distribute wear. the follower "rocks" in it's bore with each cam cycle a tiny amount. this scuffs the cylindrical portion of the tappet top and bottom, the rocking pivot point more or less in the center, but offset towards the pushrod end. it's just the sum of the leverages. this leaves (microinches) of gap, where there's no contact, the metal is darker (in the pic above). none of this is unusual or bad or anything, it's just what happens to metal in use. but after 60 years it's a lot of wear.

crankcase ventilation

it is routinely accepted that this engine consumes a lot of lubricating oil. in my experience 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). oil consumption increases when this engine is in a car driven like a sports car (twisty mountain roads and all that), which exacerbates the tendency for sloshing the oil away from the oil pump pickup... but a good PCV system hugely improves oil mess and consumption.

Oil pan

when i built this engine in 2010 i did so without using any gaskets other than head gasket and oil pump gasket, instead sealing the engine with Permatex Right Stuff. for the 2017 build, but a professional engine builder, it was assembled more normally with a Best brand gasket set. both worked, but two years later (2019) there are signs of minor oil seepage in the usual places (oil pain area mostly). the 2010 engine did not leak when it was torn down in 2017. Modern engines are assembled with goops, not gaskets.

The oil pan is ordinary enough. what i thought was adequate baffling i now see as probably a "patch" to deal with oil pressure loss due to dry pickup under hard braking. i admit my driving makes this much worse. my next engine will have some form of crank scraper and overall better oil control. for ordinary driving the stock system is adequate.

the BEST (brand) oil pan gasket set came with the wrong rear pan seal. I ended up re-using the old rear pan seal, which was supple enough, but I used enough Right Stuff to ensure it would not leak.

That nice looking drain plug is no accident. I spent a lot of time getting that right! I bought a magnetic drain plug (thanks Nate for the suggestion), and filed the mating surface perfectly smooth.

The oil pan seals to the timing chain cover at the front, which is of couse 90 degrees from the bottom of the block. This will require a back-and-forth tightening sequence to pull it into place. Easy enough.

Oil pump pickup

The oil pump pickup is supposed to have a little plastic clip that keeps the pickup from touching the pan floor. Even the TSM warns about not losing it. Mine was pre-lost. I solved this by wiring a small block of teflon -- aerospace surplus -- to the pickup. Since I'm not running a pan gasket I was concerned about the pickup hitting the pan. It's close to the teflon block but doesn't hit.

Oil pan studs, not bolts

The single biggest change to the oil pan system was replacing all the bolts with studs. Pan bolts seem to loosen with time, I'm sure it's related to shrinking and shifting gaskets, so I did this pan with studs and serrated face locknuts without washers. 2017 note: the oil pan never leaked!

timing cover installation must be completed before the oil pan can be torqued down; see that section for details.

I was very generous with Right Stuff around the rear main and seal, if you look closely, you can see that I got it to extrude between the casting and cap, eliminating yet another leak source. The rear pan seal has Right Stuff under and over it.

Here's two of the nuts visible, one on one off. The stud system was cheap, it's just grade 5 hardware from MSC Direct. The pan cannot be tightened yet, the timing cover base plate must be installed and sealed first. This was done within a few minutes of these photos.

Timing cover

The timing cover of this engine is slightly fussy, but nothing serious. This is one area AMC really improved in the new six; all of the little annoyances here were eliminated.

The timing cover is in two halfs; a base plate that bolts flat to the block and a more ordinary cover. The base plate seals to the oil pan. Pressurized oil passes through the base plate, and there is a gasket behind it.

note that there is a 1/4" NPT pipe plug in the end of the main oil gallery under the timing cover, and one on the back of the block. it is easy to forget these plugs!

install the timing area base plate, camshaft retainer, timing chain oil scraper, and the oil slinger onto the crankshaft nose. timing chain and sprockets then installs as per the TSM.

helpful hint ahead of time here: do not tighten timing cover bolts until you have read all of this section. the final, fine position of the timing cover is determined by the crankshaft seal for the front pulley/harmonic balancer. tightening the cover bolts too early may cause the seal to leak.

press the seal into the timing cover with a socket or something that presses carefully on it's steel shoulder, not the rubber. the rubber seal must remain perfectly round or it will leak.

install gasket, sealer, timing cover and most of it's bolts, loosely, so that the cover can slide around a bit. lubricate the seal in the cover and the harmonic balancer journal with oil, and slide the balancer onto the crank nose (it's a slip fit). the seal and timing cover are now centered on the shaft. timing cover bolts can now be tightened, but be warned that on this engine that the oil pan attaches to the back side of the timing cover as well as the bottom of the block; a test fit now is a good idea.

i modified this timing cover for a bracket to attach the Ford EDIS crankshaft poistion senseor (reluctor). the "36-1" wheel bolts to the harmonic balancer later.

the timing cover has a machine screw that serves as the ignition timing mark pointer. they're often bent or loose and leak oil. nothing special about this screw, hardware store 10-32. sorry, i didn't record the length.

The harmonic damper has an internal seal with a bunch of peculiar parts. This is the correct assembly order. Note that once again, a bead of Right Stuff seals it. It would be an unpleasant place for an oil seep, since the pulley would fling the oil all over the place!

The damper slides onto the crank nose, it's not a press fit. The timing cover seal is the same part as the later six right up through the 21st century.

Note that the correct damper bolt is the one with the short shoulder! I forget offhand what the other bolt is for, but it is from this motor. I cleaned all the hardware and small parts and sorted them out at assembly time.

Side covers

The very existence of these covers is comical. They're a vestige from when this was a flathead -- then, the adjustable cam followers were under there. There is no reason to ever take these covers off. their only purpose today is to leak oil. I sealed them with Right Stuff and loctited the covers on. Done and done.

Rear cam plug

What I thought was a leaking rear seal in the old engine turned out to be this rear cam plug, seeping down the back of the block under the bellhousing plate. It's at the end of the pressurized oiling system, at full gallery pressure. There's an ugly smear of sealer there that looks worse than it is. When I installed the engine, at the last second, I put a bead of Right Stuff in a circle around this plug so that the plate would be an additional oil seal, should the plug leak. I put a piece of tape across it to remind me when I'm flat on my back under the car. I don't expect it to leak in the first place, but this double-fix is trivial to do.

Into the car

It's a tight fit. A very tight fit. Allegedly the engine and trans goes in from the bottom at the factory. I forged on with a topside install.

The engine has to go in without the flywheel and rear bellhousing plate. (It has to come out that way too.) Torquing the flywheel properly while under the car is no small feat. Even without the junk on the back of the engine, it has to go in initially somewhat diagonally and rotated into place. The timing cover noses under the front brace. It's better if you remove the heater box; I did not and broke the water inlets to the heater core. A hoist with one of those longitudinal mass-shifting jobbies (shown here) makes it fairly easy. Just slow and careful.

Head gasket prep and installation

I was very paranoid about head sealing. The block deck and head surface were double-checked for flatness [2018: or so i thought; see the HEAD section] and immaculately clean and degreased. The gasket got three light coats of Permatex Copper, both sides, and I brushed on Permatex Copper around the steam holes. I bevelled holes in the head and block, though there was no sign of thread pulling, but what the hell.

The gasket was coated and allowed to more or less fully dry between coats. I assume that once in place, the solvents in the gasket cement are difficult to evaporate. The final coat was slightly tackier, and with the brushed-on spots around the holes (I mainly did that so that the micro-surface in those areas would be wetted with cement) I'm quite certain it was tight steel-cement-gasket-cement-steel sandwich.

2017 note: the head leaked anyways, between siamese pairs. likely due to the crappy deck surfacing.

Head installation

Head installation was actually a bit of an adventure. I did not want to drop the head on the sticky gasket and slide it around to find the bolt holes. My plan to install two studs and use those as guides was foiled by the fact that the thermostat pod needs to be fit under the from fender brace.

The solution was simple. I placed the gasket on the block, carefully aligning the holes by eye. I used the engine hoist and a chain bolted to the rocker shaft bosses to lower the head within an inch of the block, but not touching. I ran a couple of head studs down a front and a rear hole, aligned the head with one hand while I installed a stud with the other. Then I could just lower the head onto the gasket and block and install the other studs.

General block pictures

Just some semi-random photos of the block. Note that the old drivers-side L-head distributor hole is still there. It met the same camshaft gear, from 90 degrees away.

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