My old 250 fourtrax seems to be running with less power now. It's an '86 and I think the piston is getting worn out. How can I tell if it is worn out and if the cylinder is in good shape or not? Should this machine even be bothered being bored out to keep it alive? What will it be bored out to? Will it cost a lot?

 

I don't think the piston wears out it is probley the rings. If it is smoking or using oil thats how you can tell.

 

Get your motor hot, shut it off and do a compression test with throttle wide open and kick like crazy until the guage no longer goes up. Stock cylinder compression should be around 170PSI +/- 10. If it's considerably lower than that it probably does need to be bored, honed and a new piston installed. When was the last time the top end was taken apart and what was done to it?

 

We bought it back in '98 and we haven't done anything to it.

 

As the rings wear and the motor develops less power, this decrease in power actually protects the bottom end.... crank and related bearings. As you bring the topend up to 100+%, with an overbore, you will increase the risk of failure of your 7 year old bottom end. Bottom end failure is ugly.

If it doesn't smoke or foul the plug with oil and is still starts easily, count your blessings and ride. Haven't you noticed that the owners that have no problems with their engines year after year are the ones that do nothing to their engines except scheduled maintenance and changing the oil?