Ive got a 98 trx250 that i recently got running. The guy i got it from said it needed new piston rings. It does smoke quite a bit but was considering leaving the current ones in . What can I happen if I dont put new ones in?
If you keep the oil topped off, you can ride it for a long time with it smoking, BUT the smoking/ oil use will get worse with time, and you risk running it low on oil and doing a lot more damage.
Saying "it needs" rings is a little misleading. Cheap/ incorrect but sometimes successful way of doing it is to pull the top end, hone the cylinder, and put new rings on the piston and reassemble.
The correct way to do it is pull the top end, take cylinder to a machine shop to be measured for out of roundness and wear. Usually if a machine is smoking the cylinder is out of round and needs to be bored oversize to match a new oversized piston and ring set.
Either way you need new top end gaskets.
Of course, if it's smoking because water got in the motor, you need to tear the whole motor down and clean it out or residual grit will ruin the new top end you put on it.