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

[biljoh@xxxxxxxxxxxx]

  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. 

On October 5, 2004 Steven Holekamp wrote:

> In my limited experience I have not had any noisy pistons that had offset
> pin placement. But the 3 motors I have been involved with that did have
> this "knock" on startup were both forged pistons with centered pins. 2 of
> the 3 motors that made noise were over 10:1 compression(but had plenty of
> valve clearance and 0.050in head clearance). My old 360 and my brother's
> 401 have forged pistons with slightly offset pins like factory pistons and
> neither ever made any noise like this, both of them had over
> 0.003in.  piston clearance when new. All of these pistons are trw-speedpro
> 4032 alloy, not the soft racing pistons.
> 
> Typically(and in all of the cases above) the offset pin is in pistons with
> 4 valve reliefs and the centered ones have only 2 valve reliefs. Could it
> be related to chamber shape as well?
> 
> Food for thought......
> 
> Holekamp
> 
> 
> 
> 
> .


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