I decided to help out a riding buddy and fix up his Sportsman. The last few times that we rode the exhaust went from a small puff of smoke when snapping the throttle to a small amount of smoke all the time under regular cruising conditions. On one of the rides I wasn't on the engine died. He said that it had actually seized up and would not turn over, but I was able to easily remove the piston during teardown. I believe it may have been a heat issue.

The ATV sat for a few months....

After I tore the engine down after it had been sitting, there was water around the crank. I initially thought it was a simple head gasket problem (although I've read other possibilities since then). The top of the piston had 2 exhaust valve marks, although the valves look perfect. The cylinder has some RUST in the lowest portion. My machine shop said they could hone that out and it doesn't interfere with the piston anyway. I measured the piston with dial calipers and it is just over 87mm.... not 83 as Polaris/Wiseco says it should be. The sleeve is just under 88mm and closely matches the LA Sleeve that they sell on their site.

Question time...

Does anyone have experience with similar water/seizure issues? Is it more than likely the water seals on the pump? I'm leaning that way now.

Where the heck did this 87mm piston come from? I think that the block itself has been bored to make room for this larger sleeve, but I don't have the specs for the outside of a stock sleeve to verify. Also, if this isn't a stock piston what are the chances that the rod was changed as well? Does anyone have a good site/reference for measurements on the engine?

I'm debating on trying to hone this cylinder and finding an 87mm .020 piston that will fit or possibly getting a new cylinder/piston & possible rod. I want what will be best in the long run, I'm not looking for improved performance.


On a side note I did read that the bearings in this engine are standard size so I will be replacing all that I can, and that there is a way to replace some super expensive part dealing with the water seal problem in a much cheaper way.

I apologize up front for long first post and cramming a lot of questions into one post.

 

I may have answered about 90% of my questions. I'm not totally sure yet because I can't find the specs, but it looks like this sportsman has an Xpedition engine. The specs work out to be a 425 and the sleeve on LA sleeve is 87mm and it says that it fits the 400 sportsman and the 425 Xpedition.

The problem is now that I can't find the specs on a xpedition piston. I can find tons of pistons for sale, but I need the measurements to compare to what I have so that I can buy a .020 or so piston. Does anyone have the measurements of the piston?