Crankshaft, connecting rods, pistons, camshaft, tappets, timing chain and sprockets.
new 21 apr 2021
(This section is newly broken out, and is a bit chaotic. I am actively reorganizing it.)
the crankshaft and connecting rods are 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.
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.
Early pistons had wider top and 2nd rings. Specifics TBD here, check before buying from eBay. "Most" pistons will be the later, thinner rings.
For the 2017 engine Pete Fleming had custom forged pistons made that accept a modern 81mm ring set. the dull aluminum piston in some of the photos is a 1970's Silv-O-Lite .060" over piston from a set i purchased on ePay years ago and never used.
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.
If you think about this engine as much as I have 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
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 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.