Steve,
I would highly suspect that there is a rod bearing that is failing.
It is not difficult to remove the rod caps while the engine is still in
the car and examine the journals and bearings. If you find that there
is significant wear or scoring on either the bearing or journal, it is a
good idea to remove the piston and inspect the cylinder for roundness
and wear.
Good luck,
Joe Curry
Steve Keidl wrote:
>
> I was wondering if I could ask the list for some advice on a problem
> with my '72 Mk IV. I have been reading the list for a few weeks now and
> I see there are some very mechanically knowledgeable folks here.
>
> The engine on this car starts fine, and runs ok up to about 3K rpm when
> cold. Above that speed it starts to knock. As time goes on, and it
> heats up, the speed at which it starts to knock drops to about 2K rpm.
> This is not a subtle sound, but loud, a metal on metal sound. It is not
> pinging or pre-ignition. My limited experience with a similar sound was
> with a motorcycle with piston slap. This engine burns no oil. I
> replaced the timing chain, tensioner, thrust washers, and rear main
> bearing. No change. I looked for play in rod bearings but this was not
> easy to do from under the car. During coasting or heavy acceleration
> the knocking is almost eliminated except at over 3500 rpm. The engine
> has about 37K miles on it and shows evidence of a fairly recent (in
> miles not time) overhaul. The car sat inside from 1992 until I bought
> it.
>
> Any thoughts or comments are welcome. Any tests I can do to try to pin
> this down short of a complete tear down?
>
> BTW thanks to the folks who answered my earlier request for rear axle
> sources for my Mk III. We're still working on that too.
>
> Thanks in advance,
>
> Steve Keidl
>
> 1969 Mk III - Unsafe at any speed
> 1972 Mk IV - Work in progress
--
"If you can't excel with talent, triumph with effort."
-- Dave Weinbaum in National Enquirer
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