Rambler 195.6 OHV block

updated may 2018

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

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.

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.

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.

Oil pan

Every engine I've every built, the oil pan eventually leaks. Cork gaskets are the problem; maybe they are all just very old. This engine was assembled with nogaskets other than the head gasket and oil pump. I used Right Stuff (by Permatex) exclusively. Here's the assembly process and minor changes I made with the goal of an absolutely leak-free engine.

The oil pan is ordinary enough, but with decent baffling. Too bad the 232/258 isn't this well done. That engine gets air under the pickup in very hard turns.

I bought a new pan gasket and rear pan seal from BEST (brand) but though labelled correctly, it was the wrong part. 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!

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 to the block and a more ordinary cover. The base plate seals to the oil pan. Pressurized oil passes through the base plate too, and there was a gasket behind it; I simply circled the passageways with Right Stuff and assembled. I did a partial assembly (may or may not be visible in the photos here) so that I could torque up the oil pan before I completed the stuff behind the cover.

I didn't photograph the base plate before assembly, but you can discern which passages flow oil by the intrusion of Right Stuff into the hole which I wiped out before it cured.

When I got it assembled to this stage, I inserted the base plate to pan bolts, tightened them in sequence (pan, plate, pan, plate, ...) up to torque and let it sit overnight.

The timing cover proper was modified to mount the EDIS spark sensor. The "36-1" wheel mounts to the damper with an adapter shown here as a partial blank.

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 simply 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 left over from when this was a flathead -- then, the adjustable cam followers were under there. There is no reason to ever take these covers off during the lifetime of the motor. 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.