Pistons aren't turned very often, they are usually ground, and it's a
complex shape--tapered smaller on the top (to make it straight when
it's hot on the top and cold on the bottom) and smaller near the
exhaust valve. It's called a cam grind, though it's a lot more complex
than a cam.
You _can_ turn a piston down, You'll loose all that sophistication and
wind up with a piston that rattles in the bore, but if that doesn't
bother you it doesn't bother me. I've done it before for motorcycle
engines when I couldn't get the piston I wanted. You should do a
little taper, even just a degree is helpful. But when there's pistons
available that work just fine, and since building a motor is pretty
expensive compared to the cost of four new pistons, I don't think I'd
try that today.
On Jul 30, 2008, at 1:11 PM, Scott Cypher wrote:
> I have +60 pistons I never intend on using given SCCA limits on over-
> sizing, but the pistons are too nice just to get rid of.
>
> Has anyone taken a set of oversize pistons and turned them & the ring
> grooves down to be +40 or even down to +10 or STD so they can be
> used? I can understand the precision lathe-ing that would need to be
> done to make sure they are true, but has anyone ever tried this, good
> bad or indifferent?
>
> Thanks
>
> -Scott Cypher
> spitfireracer@xsmail.com
> SCCA #57 HP Spitfire 1500 #362573
> Reading, PA
> http://gallery.mac.com/srcypher
>
> 1971 Spit MkIV/1500 RaceCar
> 1971 TR6 TBD
> 1976 TR7 Street
> 1968 GT6 Vintage
>
> "I'm so excited I can barely sit still or hold a thought in my head.
> Its the excitement only a free man can feel. A free man at the start
> of a long journey, whose conclusion is uncertain"
> _______________________________________________
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Bill Babcock
Babcock & Jenkins
Billb@bnj.com
503.936.7660
www.bnj.com
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