<VV> Re: checking piston clearance

[djtcz at comcast.net]

snipped, and bottom posted
-------------- Original message -------------- 

 
> From: Stephen Upham 
> Subject: Rebuild II 
> To: virtualvairs at corvair.org 
> Message-ID: <90C1FC5A-1E5C-11DA-ADCF-000393902FEC at sbcglobal.net> 
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> 
> Ok, I was told to insert the pistons into the jugs (sans rings) head 
> first ( the opposite of how it would be assembled when put together) 
> up to the bottom of the crescent of the skirt. I was able to get the 
> ..002 gauge to go in on each of the cylinders, but only on either side 
> of the apex of the skirt. It was also tight as so as to require a back 
> and forth motion and it seemed as though, when the gauge would not go 
> it, that coxing it back and forth and side to side (pendulum manner) 
> allowed the gauge to insert. Once in, it moved more freely. 
> Thoughts. Do I have .002 clearance or am I fooling myself? 
> 
> Stephen Upham 
======================================================
Here's a picture of someone measuring piston-cylinder clearance on a FIAT with a feeler gage.  Note only 1 gage is used since piston clearance, like most engine clearances, is diametral, not 'per-side". 
The clearance measurement point is 90 degree to the pin. The pistons are very out of round (cam ground), on purpose. 
http://www.fiat-spider.net/servicemanualpages/Engine/images/eng-piston5.jpg
My 1952 Chilton's manual's procedure is put the feeler gage in first, then slide the naked piston in.  That's how I'd do it.
Positioning a ring in a cylinder and checking the ring end gap at several locations along the cylinder is a worthwhile check for cylinder taper.  The change in gap is ~3X the amount of taper.