Ive been having this problem with my four wheeler that it starts up just fine then as the day goes on it starts wanting to die. Once I shut the engine off it will not start back up until the engine completely cools"usually when i get back home backing off trailer. I did a compression check and only seems to be getting 80psi "if i am doing it correctly". I guess that means I need a top end rebuild. I really want to get it done locally and they told me I need to have my over sized piston before they bore it. How do I figure out how big a piston to order?

 

Time to do a topend on it.Take the cylinder and piston to the shop you plan on getting it bored at and have them mic it all out and order the piston for you.

 

make sure when your doing the test to hold the throttle wide open. it needs to be able to get as much air as possible. a *good* shop will mic the cylinder and tell you what size it needs to be able to get rid of any discrepancies in the cylinder walls.

 

Yep that is the plan

 

alright one other thing the motor seems to be really loud and making a rattling type of noise. What do I need to check that the connecting rod is ok on the crank shaft. Do you simply feel of it for play? I will be tearing the engine down tomorrow just wanted to get some info before I'm at that stage.

 

a small amount of side to side play on the lower part of the rod is ok. if you can move the rod up and down its no good. have to rebuild it (has to be done in a shop). if there isnt a lot of movement in the rod then it is probably piston slap caused by a worn cylinder. a #1 killer of pistons

 

what exactly does that mean replacing? the whole crank shaft?

 

the crand has to be pressed apart to repair the lower end of the rod

 

as in replace the bearing on the rod? I'm sorry Im just not understanding

 

slapping noise is most likely piston slap or worn primary clutch buttons