Hello all, I was recently riding my 1995 polaris scrambler 400 (no mods) at near full speed when I started to lose power and within a few seconds my engine seized. I disassembled the top end, and found that one side of the piston was broken off, and there was a good few ounces of metal crumbs in the exhaust, cylinder, and case. My cylinder isn't too beat up, and should be fine with a slightly oversized piston and a bore. I flushed the bottom end with diesel numerous times after pulling most of the crumbs out, but I'm wondering if its important to completely disassemble the bottom end to check for damage. There is no play in the rod bearing, and it turns over with ease. I'm really leery to pull the entire engine and rip into it if I don't have to. Also while I have the top end off, any recommended mods?

 

It needs taken aoart for complete insoection and cleaning or. Your gonna be doing it again! Never cut corners on a rebuild. ...

 

As soon as I saw, "my piston skirt broke" I thought it must be a 400. They were notorious for that. There's no telling what's going on in the bottom end if you don't tear it apart and do a proper inspection. And when you buy a new piston make sure it's forged like Wiseco and not cast if you don't want this to happen again.

 

Does the case actually need to be split? Or could the case be removed from the atv and cleaned/flushed and inspected without splitting the case?

My concern would be the bearings could have metal parts embedded in them and that would cause wear after the top end is rebuilt. But maybe the bearings could be flushed out.

My thought is that once you split the case after an event like this for an inspection you might as well just replace the bearings and the seals.

 

I've cleaned them after the same situation. W/O teardown you do take a chance.
Personally, after all the cleaning you did, I'd think it's good.

 

Years ago l destroyed a piston in a IT400 Yamaha l cleaned all the crumbs out just like you did the only thing l did different was l turned the engine up side down an washed the bottom end out with WD-40 spray as l rolled the engine over so l could feel any rough spots in the bearings, no problem with the new top end. The goofy thing was what caused the failure in the first place all l had done was changed to a aftermarket air filter. That was enough extra air flow to lean out the mixture. "Pop no more piston top" Good luck with what ever you do.
Tom Wecas in WY