<VV> RE; piston question

[djtcz at comcast.net]

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From: judynrandy at comcast.net 
To: virtualvairs at corvair.org 
Subject: <VV> piston question 

Since I am the mechanic taking this thing apart, I would have to say it IS 21,000 original miles.? Evidence for that fact is?that there is NO wear to speak of on the piston skirts.? ALMOST NONE!? And the jugs show almost NO wear either!? And neither do the lifters.? Then factor in?all the original type gaskets that are still there.? (Well, not anymore.)? You know, the old "paper" type that weld themselves onto things so tightly that you literally need a case of TNT to remove them!? It even had the original type? 'national' rear housing oil seal complete with part number stamped?on the edge.?And the neoprene push rod tube O-rings.?Then there are the original paint swipes on the block, diff, and trans that look like the factory ones I've seen.? Oh yeah, and how could I forget the like new input shaft!? After all that, I'd definitely say it is an original 21,000 mile engine.? Now my question would have to?be what does anyone know about?the factory installing oversize pistons in 
brand new engines?? From all of this, it looks like they did.? But what is the 'official' view? 
? 
Randy (Cap'n) Hook 
Hopewell, PA? 
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Nothing came up at my first try at scanning for oversize pistons or rings in the GMparts wiki. 

Then I found this- 
http://m.gmpartswiki.com/getpage?pageid=79942 

It says - 
(1) pistons are not serviced for Corvair - buy a cylinder assembly 
(2) no oversize rings are listed for Corvair, but are for all the other 6 and 8 cylinder engines, most with optional Cromflex rings. 
(3) the price for all Corvair crankshafts was $76.50 . 64 Turbo, 140 HP, etc. 
...... sigh...... 


FWIW, the 1965 shop manual does not offer oversize pistons as a remedy for worn cylinders or worn pistons, or even worn wrist pins. 
This is from pages 6-46,6-47. 
"If the cylinders are found to have wear in excess of 0.005" the cylinder and piston must be replaced. NOTE; Cylinders and pistons are serviced as an assembly. 

If pistons are damaged or show signs of excessive wear replace the cylinder and piston assembly. 

...the piston and pin are a matched set and not serviced separately. 
If (wrist pin) clearance is excess of the 0.001" wear limit the piston and pin assembly should be replaced." 

I guess this does not absolutely preclude the possibility of Chevy salvaging some production cylinders with O/S pistons for production line use. But I'd think the manual might at least warn the dealership mechanics about the possibility of their existence so the flat raters would have a second chance not to put oversized rings in a standard cylinder. (Although some aftermarket rings said std rings in 0.010" oversize cylinders was OK, despite an automatic ~0.030 inch larger end gap.) 

Bottom line - I'd measure the skirt diameter of the pistons marked 10, and the un-marked ones as well before assuming anything about their size. Some pistons carry various codes referencing slight variations of skirt size or wrist pin bore size to permit grading and selective fitting of the mating components.