so im pretty sure i have low compression im checkin it out tonight, but when i buy a new top end what brand should i go with? also what all comes in the rebuild kit? should i stick with the standard 72.00MM sized piston or bore it out to a 74.00MM? if i bore it out whats the power benefits? one more thing, how the hell do i bore it out? lol do i send it in and have it bored or what? thanks for your help

 

Cylinder needs to be measured to the next oversize piston that would clean the cylinder up from wear marks,ovaled,egg shape cylinder, etc.Any good local cycle/atv shop or machine shop can bore it OR Rick Ritter if you want to send it off. Wiseco is the best imo as it's a quality forged piston. Also why waste good cylinder liner material as you probably won't notice that much gain. If a 72.5 mm(first over size on Wiseco) will clean up the bore,go with that. If not you may have to go one size larger. Plus the max clearance after bore and finish honing is critical. The very most I allowed was .002,but I tried for .015 when I had the chance to break in the engines myself and didn't just bore cylinders for carry out. Piston to cylinder clearances over .005 is considered worn out!(at least by me!) The book shows std cylinder bore 72 mm (2.8346) Piston to cylinder clearance .0011-.0022 (.03-.05 mm) Service limit .006 (.15mm) too much imo. OPT

 

im thinking sticking to standard for now, if i can. i have a guy locally that can do it. id go to the next overbore size if i can. ill keep ya posted

 

DON'T stick std rings or piston back in the machine. Unless it hasn't been used very much there has to be wear in the cylinder. Have it measured. If close to .004-.005 wear from stock dimensions(72 mm) (2.8346) just have it bored to the next oversize. Will save you a lot of grief in the long run! OPT

 

The top and and crank are shot. Should I try and replace? Find new motor or cut my losses?

 

Have the engine rebuilt if you plan on keeping the atv. Buying a used engine wont help one bit. You'd probably have to do the same with it! I've had this same conversation dozens of times with customers over the years and gave them the choice. You can buy the parts yourself (Hot Rods makes a good cheap rod kit), have a machine shop or dealer install it and true the crank,have the cylinder bored out,you can reassemble it and then you'd have a machine that would last for years if you take care of it. OPT

 

its rusted pretty good in there. could the crank be sanded down and cleaned up? where can i find cranks? i can get a top end. but it seems like a lot of work, my mechanic friend has it right now, i jut dont know what to do, i wanna rebuild it but cant find any freakin engine parts!!!!

 

Here's an example. Polaris Trail Blazer 250 1990 2003 Connecting Rod Kit New | eBay Just give the crank to a good machine shop or dealer to install. The 3 crank bearings you can match up at Napa,etc and not have to pay dealer prices. Cranks seals are cheap,just get at the dealer. Then a Wiseco piston and bore the cylinder. Complete gasket kits are available on Ebay also. Doesn't have to cost an arm and a leg if you can assemble it back yourself! OPT

 

suposedly the case didnt have a good seal and water got in there somehow? idk how ( i paid a dollar for it and pulled it out of a dusty barn and blew it off with a compressor) but water did get in there and my mech, said its all rusted and he pulled of the rod and said that it wiggled?? idk. but he says my cranks done for, is it done for or can a machince shop clear the "rust" and make my old crank work?? or do i need to find a new one? from what i was told i need a new top and bottom end so what should i do? i already am getting a topend rebuild and a carb rebuild kit. but what about the bottom end??

 

That's why I posted a link to the rod kit so you can have the crank rebuilt! Very simple engine and parts aren't that expensive compared to a lot of others. The main cost: rod kit about $70, piston kit about $100, bearings about $35 or less,seals about $16,gasket kit about $30 or less. $250 in parts plus labor for the rod kit installation and cylinder bore!!! Either rebuild it right or I wouldn't waste my money on just a top end only that probably wouldn't hold up! It would just be good money thrown away! OPT