I recently bought a trailboss at haydays and found out the water pump seal had been leaking for quite a time thus destroying the bearings and rusting everything else. I would like to find a complete bottom end for this 350l #w927539 since the upper end is still good so i can at least feel that i wasn't screwed.

 

Ebay,Craigslist,etc is your best places for used cases(if this is what is needed) Counter balancers are the problem and the most costly item. I haven't rebuilt one as Polaris doesn't offer a replacement bearing for this,but have heard of people pressing off the outer gear and finding replacement bearings at a bearing house. The gear and shaft have to be marked to align the balancer back properly.Plus if the shaft itself where the pump seals ride is scored,will have to be cleaned up/resurfaced wit an epoxy of some sort to make it even work! This 350 along with the 400 engine can be expensive to rebuild. Coolant can eat up bearings in the counter balancer/water pump cavity along with messing up oil pump drive gear and shaft. Don't trust used counter balancers! Could have the same problem as yours. A new one is close to $500 now. OPT

 

I just rebuilt my 1991 trail boss 350 and it was easy. the counter balance also is what destroyed mine, along with the case. the counter balance smashed the bearings right thru the case. their are a few counter balances online on ebay for about $150 or less. bearings for crank and the cases cost me right at $50 their was a guy on ebay that actuall regrinds and repairs your old counter balancers, sorry I don't have his contract info. 2 cycle engine is simple to rebuild if all you need is gaskets, bearings and a water pump balancer, good luck

 

just happen to come across the person on ebay, that rebuilds these water pump counter balancer's. hope it helps ya.
Polaris ATV 400 350L Counter Balance Shaft Water Pump Repair Balancer | eBay

 

Good listing! A machine shop service like this has been needed for years!. This was the largest major expense on rebuilding the 350 and 400 outside of rod kits/pistons and cases. More people can keep these old atvs on the trails. OPT