Re: [AMC-list] caspers motor may be ok, but need advice/suggestions

[tom jennings <tomj@xxxxxxx>]

Even after disassembly I never found the source of the odd mild at-idle
"knock" from the crankcase! It came out of the oil filler neck, so it was
definitely down the bottom end. It behaved exactly as if it was the fuel
pump cam hitting the fuel pump lever. If you revved it or even just blipped
the throttle, it went silent, then a few seconds later it would gently get
louder. Not loud though, just tank, tank, tank, tank, ...

If you picture what the fuel pump diaphragm is doing down there, the lever
pushes the diaphragm up against the spring, and it fills with gas. Lever
falls back down, and the gas tries to press out towards the carb. But at
idle the carb is full, the needle is against the seat, so the gas only seeps
out of the pump. Next time the lever comes up, the diaphragm is still full
of gas, and there's a big gap 'tween it and the lever. >TAP< as the lever
moves through open space and just taps the almost-full diaphragm just a tiny
bit.... rev it up, the carb takes fuel, the diaphragm drops, the lever hits
it earlier, it's quieter. That's all I could figure was going on. All the
bearings were very worn, copper showing and abrasion, but nothing broken,
gouged out, loose, etc, just lots of years and miles. Cam had that mild fine
black pitting from wear with no oil filter, no fuel cam wear, etc.

Who knows.

If the new motor makes the same sound I'll be sure it's the pump business.

The frustrating thing to me is, I might not get to crank it over again until
8 May, unless I can do it Monday. Awful schedule.



Detonation, I don't think that's it. I'm no engine designer, but that
combustion chamber is a screwball design. It's got a ton of surface area,
weird pockets, far too many sharp edges inside, the bores are round of
course but the head chamber is not and overlaps the block top, etc. Weird. I
bet all sorts of things go on in there.

But when I was playing with ignition advance timing, I definitely got it to
knock with far too much advance, and it NEVER MADE A SOUND. The engine
"sounded funny" out the tailpipe, power was way off, and I did hear what was
probably the knocking sound, twice maybe, but not like any other engine I've
ever heard, ever. It wasn't sharp at all, more like tapping a large clay pot
with a stick, and not the 'marble in a beer can' sound that the 232 makes.
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