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Ski-Doo: S-2000 and older 1998 and older, all models in the S-2000 chassis and older chassis models
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Old 01-04-2019, 02:09 AM
le700 le700 is offline
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Default Rotax 670 piston size

I have a 95 SD Mach-1 670, that I am giving a light rebuild. The motor is stock, and I plan on doing the pistonrings/pistons for preventive maintainance, in addition to crank seals. But only the lower ring is available from doo.

The piston size is 78,0mm, and it is also discontiuned from doo (complete piston). But they have replaced the piston part number with another, that is 77,9mm.
Would that fit, or would it break prematurely do to the wrong size?

The case is that I bought a set of oem gaskets and seals with 2 oem 77,9mm pistons and some crank bearings for real cheap.

Would it be safe to use, or should i search for 78,00 rings/pistons?
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Old 01-04-2019, 12:30 PM
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bore is 78
piston is 77.9

can verify with snap gauge and mic...
piston should be .005" smaller (measured at skirt bottom) than bore-BJ
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Old 01-05-2019, 01:16 AM
le700 le700 is offline
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Thumbs up

Thanks for the reply.
I was unsure because in this list where the replacement is used, it looks like it fits both 77,9mm and 78,00mm.. So it looks like there are two different bores. But as you say, I am just a measurement away from the answer. So thanks again.

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Old 01-06-2019, 10:23 AM
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doo did have .010" over 670 pistons...

a simple bore/hone is all that is required if you want factory pistons-BJ
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