piston Slap

["Phemister, George" <PHEMISG@xxxxxxxx>]

<<<<<<< Kyle writes:	Subject: Re: M20 Piston slap

It would seem to me that *if* this noise is indeed
piston slap that it would worsen as the engine gets
warmer - the metal would expand and contact would
worsen.  The result of piston slap is bent valves
and/or valves that eventually fail to seat properly. 
The solution would be to take the head off (inspect
while you are there) and install two head gaskets.  If
a bearing is loose, a more probable reasoning, it
seems that heat could expand the metal around it and
possibly curtail the knock noise at operating temp. 
These are just my observations, YMMV. >>>>>>> 

I believe the more common use of " piston slap" is to describe excess wear
on the piston skirts, which when combined with bore wear, allows the piston
to wobble in the cylinder. As the engine warms up, the piston expands
slightly and usually the noise goes away after a few minutes. This amount of
wobbling shouldn't  bring the piston into contact with the valves. For a
street engine, I wouldn't rush to rebuild unless it's getting bad, because
you'll need new oversize pistons.

If the noise gets worse as the engine warms up, and/or as the revs go up,
then you got another problem - maybe a rod bearing, maybe excess pin
clearance. In that case, it's rebuild time ( or wait till it blows).

Another easy thing to check is cam chain tensioner. On M10/30 engines, the
tensioner piston and bore can wear, allowing the chain to rattle as it whips
the casings. Look for wear grooves on the inside of the timing covers. The
sound will be at the front.

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