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Pro-X pistons and engine components

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I purchased a brand new top end kit from eBay which included a Pro-X 13.5:1 piston. When I took it out of the package I was surprised what it looked like, then realized it was made in a casting process. A little search online confirmed that as well. In that search I heard about reliability issues in two stroke applications but nothing about a high compression four stroke.

My 2009 KX250F currently has a JE 13.5:1 forged piston, along with PC cams, ti valves, springs, porting, and I use a mix 50/50 of VP C12 and pump gas. My question is should I sell the Pro-X piston and purchase another forged piston for peace of mind? Or will this cast piston be fine? I will probably replace whatever piston I choose after less than 50 hours anyways. Thanks 👍

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Motorcross Action mag did a nice write up on pistons. They stated all 4 strokes come with forged pistons from the factory.

So I would stay with the factory specs. Good luck.

Mark

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forged pistons are stronger but they can be less stable dimensionally compared to a cast piston. cast pistons can have more silicon which helps them stay very close to the same size even at extreme temps. forged pistons have grain alignment due to being pounded into shape that makes them able to withstand more of a beating without fatiguing. In addition the cast pistons can have spots that are not uniform in material properties, or voids, and this can lead to a stress concentration, crack growth, and failure eventually. Forged and cast pistons both have properties that are desirable. The pros can get a semi-forged piston that has the best of both worlds, but they are not available to the public just yet. And the OEM pistons from the japanese bikes are mostly cast, not forged, weather 2-stroke or 4-stroke. If you watch your piston and change it out regularly, you should be ok with a cast one. 50 hours seems a little bit excessive for a 4-stroke race bike though. Maybe 30 is safer, or at least change the rings at that point. They will go bad before the piston does in most cases. Also be sure to measure your bore and the piston and make sure they have the correct clearance from your manual. Same with the new rings...check the ring end gap. Pro-X pistons are usually made by ART, and they make the OEM pistons for a lot of the japanese bikes too.

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