wardntx

I am new, of course and apologize for just starting a new thread. But I need some information and advice.
I have a 1998 STX900. The back piston has no compression so I pulled the head and it needs to be replaced. In fact, the second piston needs to be replaced as well as it it heading in the same direction as the back one.
I did not pull the engine from the boat.
Is it possible to replace the pistons without doing so? I have taking the flame arrester off the carbs, loosened the water and exhaust from the other side but cannot pull the cylinders up to get the pistons out. Probably the gasket holding it on.
I have never worked on a jet ski motor but I am pretty decent with mechanical repairs. The front piston actually looks to be in pretty good shape. Very good actually, other than some carbon on the top. (can this be cleaned off).
It looks like someone use some type of gasket sealant on the head gasket and it sealed off some of the water ports. It might be hardened sand or silt.
The jet ski ran pretty well for a while but I don't know if oil was not making it to the cylinder or the water was not cooling much. Just trying to provide a little history or information that lead up to where I am now.
Back to my immediate issue, do I need to pull the motor out to pull the cylinders and replace the pistons or can this be done without doing so? I am sure it would be much easier on a bench, but I am not looking forward to pulling out the entire motor and may just sell it rather than try to fix it.
But the piston sets are only around $80 each and if I can do it without pulling the motor, I may give it a shot.
Also, the head has some burrs on the top of of each piston port. Do they resurface these?
If it will let me post pictures I can , or a link to some.

I really can't find much on the net regarding piston replacement for this motor, so if anyone has any links, please post them.

Thank you
Ward

topbloke

im not clued up with the stx but if its near the same as my zxi 900 i might be able to help...
first off i would pull the engine and rebiuld it on a bench this way you have more light and easier access to clean surfaces and more room to move around .. infact it seems like you nearly got it out [carbs off exhaust off front stater cover off engine mount bolts slide forward to get past the coupling and then lift out ..once you got it on the bench remove the block check the block for scoring it may need to send off to clean up.if the block does need cleaning make sure you get the right size piston and rings to match . it does sound like its only the top end but while you got the engine out clean and inspect ..now you are going to need gaskits dont use the old ones ...are you still running oil injection??????? if so remove and block off and run premix 50.1 you cant go wrong unless you forget to add oil in the fuel... let me no how you get on or you need some advise ill try to give but like i say i dont no this model very good