SPI piston question

RevXP_08 · Feb 10, 2015

So I have a 2001 summit 600 that I've had to rebuild a couple times. The last time I ordered SPI pistons .020 over as I had my cylinders bored. The sled blew up again and I got to measuring the pistons and their just under 76mm which is stock bore. The pistons say right on top that their .020 over which should be 76.5mm. And inside the piston it has a part number. After looking it up it's for standard bore. My question is why does the piston say .020 on top of the piston but has a stock bore part number and the piston is stock size?

Jonathanpitzl · Feb 16, 2015

Me and my buddies always put spi pistons in the zx sleds and never have a problem. im guessing just a mix-up at the factory, good pistons for the price IMO, just always measure your parts before install to make sure there is no mix-ups like what happened to you and then if it does blow up you would know wrong sized parts were not the problem

LRD · Feb 18, 2015

Not being sure where your at with engines and the "Knack", no offense meant, but did you measure at the bottom of skirts and not at the top. The tops are always quite a bit smaller than the bottoms. Tops of the pistons run at 300 to 400 degrees or more and expand a bunch.

I just measured a new Wiseco 670 piston going in my 500SS big bore and about 10 thou smaller on top than bottom.

Good Luck

Kawi · Oct 22, 2015

spi

Either way, you should buy the pistons before you bore the cylinders and have the machinist match them to the cylinders.

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SPI piston question

RevXP_08

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Jonathanpitzl

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LRD

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Kawi

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