Forged Piston Noise when cold, Piston material or pin placement?

[nick.alfano@xxxxxxxxxx]

This is a false statement.  Forged pistons do not make more noise during start
up than cast pistons.  It has more to do with piston to wall clearance and
floating pins Vs pressed pins than cast piston Vs forged piston.  A looser
clearance for more of a race application will have some noise with cast or
forged.  It seems to happen more in pistons with floating pins than with
pressed pin in my experience.  I have had stock cast piston AMC engines that
made this same noise and nothing at all was wrong with them.  Ran one engine
for 100,000 miles with no problems.  My full floating forged engine makes some
noise almost all the time but it was machined loose to rev faster.  Another
engine we have with forged pistons and tight clearance makes no noise at all.
In fact, I had a GMC Yukon with the 350 (since we are bringing the LS1 engine
into this) with a cast pistons that had this same noise almost every time I
started it cold.  It was a wrist pin noise.  Went away after a few seconds.
A racing style forged piston wants a looser clearance but a standard style
like the regular TRW/Speed Pros forged don't require as much.  In either case,
there is also a range from tight to loose for that particular piston that you
can stay within.  Stay on the tight side, little to no excessive noise.  Go on
the loose side, piston noise increases most likely coming from the pin not the
skirt.

Nick Alfano


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Date: Tue, 05 Oct 2004 22:17:38 -0400
From: biljoh@xxxxxxxxxxxx
Subject: Re: Forged Piston Noise when cold, Piston material or pin  placement?
To: mail@xxxxxxxxxxxx
Message-ID: <ADVANCES62A1XvpFVjC0000003e@xxxxxxxxxxxxxxxxxxxxxxx>

  Forged pistons will make more noise on a cold motor than cast pistons until
the engine warms up.  I would imagine that as the engine wears over time the
cold noise could get louder/worse as the cylinder wears increasing the
clearances even more. "over .003" could now be over .005. Piston side skirt
wear and cylinder lning wear combine.  This is a common problem on modern
engines using forged pistons most notably LS1 motors that have had lots of
comlaints about piston slap on start-up. The pin placement may or may not make
the situation worse I have never researched that but someone here will be able
to adress that.