Oversized Pistons, was piston ovality on AD

[AlfaNeely@domain.elided]

In a message dated 12/18/2002 2:36:49 PM Central Standard Time, 
owner-alfa-digest@domain.elided writes:



> Date: Wed, 18 Dec 2002 11:06:49 -0800
> From: "Stefano Iachella" <iachella@domain.elided>
> Subject: Re: piston ovality on AD
> 
> <snip>
> 
> How about an oversized piston? Other cars do this (I've heard) and
> motorcycles too. Are there any pistons suitable to Alfas that are slightly
> larger?
> 
> Stefano
> Oakland, CA
> 

       With the replaceable cylinder liners on an Alfa, there is no reason 
for a "slightly" oversized piston.  If the Alfa cylinders get worn, you 
replace them and the pistons at the same time.
       Most cars do not have replaceable cylinder liners.  When a car with 
the cylinder cast in the block becomes worn, you have to bore or hone 
oversize and fit oversized pistons.  That or buy a new engine block.  Thus 
pistons are generally offered in oversize increments of 0.010 inches.

       The other reason for boring the cylinders oversized and putting in 
larger pistons is to increase displacement.  Many racing organizations allow 
oversized pistons.  That started to allow those with old worn cylinders to 
run the old engine block.  But for the racer, all engines are automatically 
bored to the maximum allowed by the rules, no matter the need.
       I fitted 85 mm pistons to my SCCA ITB race car.  The rules allow 0.040 
inch overbore, which happens to be almost exactly one millimeter.  I bought 
special stock compression ratio pistons from Paul Spruell.  The rule book 
specifies that the compression ratio cannot be increased more than half a 
point.  I also had to have the stock cylinder liners bored / honed 1 mm 
oversized.  Paul Spruell also performed that operation.  The cost was roughly 
three times the cost of new standard sized Borgo pistons and liners, plus I 
had to buy rings separately.  But, hey, my 1962 cc engine is now 2008 cc!
       Sperry or someone sells special 85 mm liners, but they are rather 
expensive.  It is cheaper to have to the stock liners bored out.
       I am not aware of any kits offering increased displacement as part of 
a normal overhaul.  There used to be a kit for the 1300 Alfa to increase it 
to 1400 cc.  I think this might be a marketing opportunity.

Ciao,
Russ Neely
Oklahoma City
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided