Camshaft and timing chain and sprockets

Camshaft, camshaft sprocket, chain, crankshaft sprocket, tappets.

21 dec 2023

Overview

Camshaft

It should be no surprise that there are no (and never were) aftermarket performance cams for this engine. A used cam must be reground, but because the base circle is only .020" or so larger than the rough casting increasing lift or duration is not possible. I've done this, twice, and don't think I've really noticed any change. If you think about this engine as much as I have (no comments please) you'll eventually stumble upon the idea of puttimg an L-head engine camshaft into the OHV block, since it generates significantly more lift at the lifter. Alas, it is not to be. Here is a quick camshaft comparison.

The BLOCK section contains camshaft bearing information.

Camshaft timing sprockets and chain

The aftermarket calls the combination of the two sprockets and chain the "timing set" and you could once buy kits for this engine. Be extremely wary of bad information, measure if in doubt. The aluminum engine parts, and L-head parts, " looks like" the OHV's but are not usable, and are easily found on eBay because no one wants them.

The following is always true for the timing parts for the 195.6, 184 and 172 engines back to 1946. Count the links of the chain. I believe the list of applications is: 1946-1948 Nash 600, 1950-1956 Nash Rambler, 1958-1965 Rambler American.

Specifications for all cast iron 195.6 engines
Camshaft sprocket 46 teeth
Crankshaft sprocket 23 teeth
Timing chain 60 teeth

All OHV engine timing chains are 1" wide, and the teeth of OHV sprockets are 3/4" wide. There exist 3/4" wide chains and 5/8" tooth sprockets. These do not fit the OHV engine. I presume they fit some L-head engines.

These are the correct part numbers for the 195.6 OHV engine timing components. As of this writing Egge Pistons has these parts available. They are the correct part for the engine, I've installed them and verified the numbers, which are stamped on each sprocket.

Cam sprocket 317 5869, #229
Crank sprocket 317 5870, #230
Chain 312 5871, #339

1-inch crankshaft sprocket closeup.

Approximate sprocket width, for 1-inch chain.

1946 (Nash) to ... 3/4" L-head chain timing set

I think -- not verified -- that the 3/4" parts are for L-head engines. They do not fit the OHV engine. I bought a Melling #365 and it is 3/4" wide.

Cam sprocket 312 2388
Crank sprocket 312 2389
Chain 312 2392, Melling 365

Here is the RockAuto Melling 365 info page.





Tappets

Do not use resurfaced tappets!

For my 2010 build I bought used but resurfaced tappets. This turned out to be a mistake, as the resurfacing 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.

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 Kanter. 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 (rocking) 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, it's just what happens to metal in use, but after 60 years it's a lot of wear.

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