Im new here so please forgive me if i post in the wrong page.

Alright, so i have a polaris sport 400 (1998). put a used carb on her from my totaled xplorer 400 and while i was at it, i pulled the reeds off to check for scoring. What i found suprised me, it still had the stock piston with barley any scoring! I heard that the stock piston on the 400s like to drop the skirts. Ok, here is my question - will the piston skirt break along the scoring lines if it had scoring?

Any feedback would be helpful!

 

Yes they had a habit of braking skirts on stock cast pistons mainly when really worn. People just letting them wear too far was the main cause imo and not that they were that brittle. Granted Wiseco forged pistons are stronger and won't usually do that Check compression as that's the main thing to check as a piston can still look good,but compression can be lower than recommended. Only other way is take the jug off and check piston to cylinder clearance which .005 is the limit. I've had them come in with over .008 and some more than that with broken skirts. If you take the jug off,you might as well throw a new over size Wiseco piston in with a fresh bore and hone job.That way the worry is over and can possibly save more expensive repairs if the skirt did actually break. That's also when engine case damage can happen making it an expensive job.

 

So i checked compression when i got it, it read 135 to 145. Is that in the safe - zone? And also i looked for a wiesco piston for my model, they dont seem to manufacture them anymore but had plenty on ebay and some other sites.

thank you so much for your help!

 

135-145 psi is plenty good enough,but you might want to snag a first over size Wiseco piston kit along with new gaskets and have them handy if you plan on keeping the machine.

 

I looked for a Wiesco piston kit, they seem to not have them available. they did have some on Ebay though.

 

Still shows them on their piston kits pdf but things may have changed.ATV Forged Pistons & Performance Parts - Wiseco Piston Inc.