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Any 1 seen a piston like this

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I think it is either off a honda 2001 or a yam 02 125. Just asking coz some of the bikes I had when I was young were tuned and i have a 08 yz125 now and the piston is the same size. What is the big hole in the intake side for?

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It's a window for the boost port in the back wall of the cylinder. Lots of bikes have them.

As the piston travels up from bottom dead center the hole allows the intake cycle to start sooner, controled by the reeds and crankcase pressure (vacuum), and not by the piston blocking the intake port (such as in old piston-port engines with no reeds).

As the piston travels down from TDC the port controls flow to a boost port in the rear portion of the cylinder. Also helps cool the piston crown and cool/lube the wrist pin bearing.

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It's only for 2 strokes. My mate reckons he has one on his 4stroker. Would that be to save weight? Anyone that knows?

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It's only for 2 strokes. My mate reckons he has one on his 4stroker. Would that be to save weight? Anyone that knows?

While it could be possible to run a setup like that in a 4 stroke, you are right, it would only be fore weight savings. I have not seen one myself, though.

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It was just because all the pistons I have bought for my yz dont have it in

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