<VV> Piston Slap - Pin Offset

Hugo Miller hugo at aruncoaches.co.uk
Mon Nov 4 05:28:50 EST 2019

Interesting - you mean offset across the engine, not in line with the 
crank? I've never heard of such a thing. Not saying you're wrong, just 
that I've never heard of it. I did hear of one engine (Cadillac maybe?) 
where at some point in mid-production they reversed the pistons as this 
made them quieter. But I have a feeling that this was a split-skirt 
piston. Frankly I'd be surprised if a fifty or sixty thou offset mould 
make much difference to anything, but that's just my opinion of course. 
Most pistons in my encounter have an arrow or similar denotng which way 
round they should be fitted.
How would you even notice such a small offset I wonder?

On 2019-11-04 03:27, edward szuch via VirtualVairs wrote:
> Regarding the piston slap discussion.......
> When you installed the new forged pistons, was there a way to 
> determine if
> there was any piston pin offset in the piston and if so, did you take 
> this
> into account when installing the piston on the rod?
> The Chevy shop manual makes no mention of this because they always 
> refer to
> keeping rod, pin and piston as a complete set from the factory, which 
> would
> have the correct pin offset.
> However, pin offset is very important for noise in particular and I 
> know of
> no engine that doesn't have some amount.  Pin offset tends to 
> transmit
> combustion loads more gradually to the skirt (cocking in the bore) 
> and
> minimize slap.
> If you have a copy of Bill Fisher's "How to Hot Rod Corvair Engines" 
> you'll
> see a couple of paragraphs on the subject on page 58 (revision III).  
> It
> says there is a 0.055" - 0.065" pin offset on the stock Corvair 
> piston.  It
> gives a brief sketch and instructions for ensuring the correct 
> rod/pin
> installation.  I'm not sure what your forged piston has for offset 
> but it
> should have some.
> It only takes one of them to make noise and since I saw no mention of 
> it in
> your e-mail, I thought it might be worth consideration.
> If you don't have the Fisher book, I could try scanning the page and
> e-mailing it to you.
> Hope this helps.
> Gary Szuch
> 248-600-7473
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