Block, crankshaft, connecting rods

Crankshaft, connecting rods, pistons, oil pan, side covers, harmonic balancer, installation.

updated 13 dec 2023


block variations

195.6 OHV cast iron engine blocks are mostly interchangeable. In 1959 the coolant pump moved into the block (was behind the generator), engine mount bosses added for newer chassis, in 1961 cam bearings changed, in 1963 timed top-end oiling feature was added, and in 1965 full-flow oil pump and filter added. All of these differences obviously deserve a detailed breakdown, but I haven't got to it yet.

The differences in engine block lubrication are covered in detail in the OILING section.


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.

The pistons for all 172, 184 and 195.6 OHV engines should (...) be the the same design. It is possible that there are variations in ring thickness in earliest years. To the best of my knowledge the ring thicknesses are:

Top ring 5/64"
Second ring 5/64"
Oil ring 3/16"

The L-head engine's pistons are flat on top, and rings are all 3/16". Be careful when buying rings, pistons and other engine parts: parts sellers may list them simply as "195.6" or "196" and either not know or not care about the differences. We've all got the wrong parts languishing on our shelves from not paying attention to details!

The 2017 engine in the roadster got custom forged pistons, lovely and expensive things...

Camshaft bearings

Camshaft-timed top-end oil

The hard-won knowledge in this section was worked out by user wittsend, I've placed it here, edited, with his permission.

Nash then AMC, went through three different camshaft bearing designs in the 1940's through 1965. From Nash through 1960, late-1961-up, and 1963-up. The AMC Factory Parts catalog (Group 1.40) lists only two bearing sets for all (AMC) years starting 1960 when the catalog was published, which could mean that the oldest system isn't in this catalog.

In 1961 the camshaft journals, and the block camshaft bores, were enlarged. All engines after this change have the same diameter. Bearing inserts for this change pertains to 1961 and 1962 engines.

In 1963, and for OHV engines only, AMC changed the top-end (rocker) oiling system from "full time" (head pedestals fed from a steel tube run up from the main oil gallery) to "timed oil", where block, camshaft and front camshaft bearing were changed to interrupt the oil flow to about 40% of the previous system. These bearings are the same as 1961-1962 with the addition of additional holes and a gully on the front insert. If you use timed oil ensure you have the correct front bearing.

If you cannot use the correct bearings in a 1963-up block, it is possible and reasonable to revert to non-timed oil and feed the top end from the main gallery. This will require replacing the steel tube feeding the head. My roadster runs this way; I've found no downside and I run that engine very hard.

This is the 1963-up timed-oil front bearing. The through-1962 and all L-head bearings will look the same except for the extra hole and gully.

This is the insert for positions 2, 3, 4.

Here are some aftermarket parts numbers to guide you in your search, once again courtesy wittsend.

Late 1961 and 1962:
N-5 Dura Bond
1193M Federal Mogul
944CS Michigan
SH470S unknown
S295P unknown
CBS 131 unknown

1963 thru 1965:
N-6 Dura Bond
S321P Johnson
PSH-529S [2441106] Perfect Circle
935CS Michigan
1219M presumed Federal Mogul
SH529S unknown
CBS 151 unknown

crankcase ventilation

It is routinely accepted that this engine consumes a lot of oil. In my experience most of this is oil mist drawn through the PCV system (or out the road draft tube). Oil consumption increases with operating RPM; about half a quart per day driving 1000 miles at 65 mph and above (2800 - 3000 rpm). A good pcv system hugely improves oil mess and consumption.

timing cover

The timing cover of this engine is slightly fussy, but nothing serious.

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 factory service manual.

do not tighten timing cover bolts until you have read all of this section. The final position of the timing cover is determined by the crankshaft seal for the front pulley/damper. 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 damper journal with oil, and slide the damper 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.

Don't leave out the oil gallery plugs!

Don't forget to install the front and rear main oil gallery plugs!

In these photos, the engine is on a stand and shown at various rotations; the big sprocket is the camshaft, the small one crankshaft. Sorry for the dizzying perspectives.

On the roadster's motor I added a bracket to attach the ford EDIS crankshaft position sensor (reluctor). the "36-1" wheel bolts to the harmonic damper 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. I didn't record the length.

oil pan

The oil pan is ordinary enough, with a small baffle at the front to lessen air in the pickup under hard braking. In modern city driving the occasional panic stop does cause momentary oil pressure drop. All of my engines have done this, it's alarming nonetheless.

My 2010 build was assembled with no oil pan gasket, instead sealed with Permatix Right Stuff. It never leaked; pulled out of the car for the 2017 it had not developed even one oil leak. The 2017 build, in the hands of a professional engine builder, it was assembled more normally with a Best (brand) gasket set. Two years later (2019) there were signs of minor oil seepage in the usual places. Modern engines are assembled with modern goops, not gaskets.

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 90 degrees from the bottom of the block. This requires a back-and-forth tightening sequence to pull it into place.

Timing cover installation must be completed before the oil pan can be torqued down.

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, grade 5 hardware from MSCDirect. 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.

side covers

The very existence of these covers is comical. They're a vestige of it's mutation from a flathead -- for the flattie, 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 loctite the covers on.

Harmonic balancer

The harmonic balancer has rubber that goes bad with time and use. They need rebuilding every 20 years. I use

They're an easy slip fit with a key, so you can't go wrong installing it. But there is wet oil on the inside and so the weird and complicated seal is necessary else it will fling oil everywhere. It's easy to do right. I add a wipe of Right Stuff for added insurance. Shown below is the correct sequence of parts from the service manual.

general block pictures

Engine installation

The engine and transmission was inserted as an assembly from below at the factory. Not so easy to do at home. Most Rambler Americans have had the front cross-brace cut out for this reason; it interferes with inserting the assembled engine from above. It's still not all that easy.

I decided to install the block minus head, and put the head on in the car. That's generally how I do it today, but I don't use the factory headbolts, I use studs from ARP. Besides more positive control over cylinder head torque they make excellent guides for the sticky gasket and cumbersome cylinder head.

Head gasket sealing is a serious problem with these engines and it takes a lot of care to get it right. The modern sandwich-type gaskets aren't available, pretty much the one ld stype from Best Gaskets. This engine has less sealant than I use today. I fully coat both sides of the gasket and let it dry, drier than recommended. I also brush sealer around the problem areas on the drivers-side of the block, around the coolant passages.

Sliding the gasket and heavy head around on the block is always a problem, but the studs made this much simpler. I insert four (two would do) studs as guides for the gasket, then the head itself, which is lowered by the crane. I neglected to take any photos of the head installation.

I'm highly dependent on that crane trolley (red in the photos). Without it I was always prying and pushing. With the trolly installation goes smoothly and easily, requiring many fine adjustments to height and tilt, but nothing gets bent, broken, no stressed parts. Tilt and adjust until it lines up and falls into place.

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