Piston help

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Piston help

Postby Neil350 » 03:44 am Feb 27 2016

I am doing a top end refresh on my 1999 KDX220, I have a new Wiseco piston to put in, but the old piston coming out is a Wossner, their is a difference in that the Wossner piston has a small port or cut out above the gudgeon/wrist pin but the Wiseco does not have this.
What does this port do and should I use the Wiesco piston that doesn't have it?

Thanks all

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Piston help

Postby Tioli » 06:41 am Feb 27 2016

Someone else will answer the if wiseco with out a rear port is the correct one as I don't know.

What the rear port does is on the up stroke suck fresh charge in to fill the void under the piston, cool and lubricate the judgeon. On the down stroke some charge will go back out and help feed the rear port at the back of the cylinder cool and lubricate the judgeon. If the wiseco does not have a rear port then it should have quite a large cutaway up on the rear skirt to help do those things.
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Piston help

Postby pumpguy » 11:09 am Feb 27 2016

Not familiar with Wossner pistons for KDX 220s, but if it's above the wrist pin, most likely it's just a cavity from the forging process to reduce weight. A port through the piston at this location would have to line up with a transfer port in the cylinder to have any value or use.

The boost port that Tioli talks about would be in the piston's rear skirt, and that would line up with the cylinder's rear boost port. Kaw and others have changed the size of these over the years IIRC.
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Re: Piston help

Postby Jaguar » 05:37 pm Feb 27 2016

just go ahead and use it
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Piston help

Postby Tioli » 06:23 pm Feb 27 2016

Now that I have read pumpguys response I agree with him
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