94 xp 657x low compression in pto cylinder

[Snowmakerdrew]

Hi everyone, new to Jetskis but have done a lot of work on sleds and dirt bikes. I picked up a 94 Xp with the 657x. It starts and runs good but when compression testing I am getting 135 psi on the mag side and only 105 on the pto side. Rings and pistons? Any other common problems to watch out for?
Thanks!
Drew

 

[mikidymac]

Engine is shot.

150 psi is perfect and it’s done at 120 psi.

Even if your gauge is reading low you have a 30 psi difference between cylinders so at least one cylinder is bad.

Your only option is to get oversized pistons and rings and have the cylinders bored oversized.

I would also inspect the crank bearings and at minimum install new outer crank seals and pressure test the engine.

Finally you have to rebuild the carbs with only genuine Mikuni parts and new needles and seats. Also full rebuild of the fuel system.

 

[etemplet]

Nice lookin ski.

 

[Snowmakerdrew]

Engine is shot.

150 psi is perfect and it’s done at 120 psi.

Even if your gauge is reading low you have a 30 psi difference between cylinders so at least one cylinder is bad.

Your only option is to get oversized pistons and rings and have the cylinders bored oversized.

I would also inspect the crank bearings and at minimum install new outer crank seals and pressure test the engine.

Finally you have to rebuild the carbs with only genuine Mikuni parts and new needles and seats. Also full rebuild of the fuel system.

As to what extent is it shot? I’m used to dirtbikes, hone the cylinder and throw a new piston and rings in it. Replate them at millennium if necessary. I guess I’m not 100% sure why I would need to go oversized?

 

[Snowmakerdrew]

Nice lookin ski.

Thanks, now only if the compression were in balance I’d be a happy camper lol

 

[Snowmakerdrew]

I will send them off and have them redone. Any suggestions on where? I’m in MI if it helps. Is there anything I should know about removing the engine? Or a good thread that has all the info I may need? Thanks for the help.

 

[mikidymac]

The cylinders are iron and not plated so they wear along with the rings and pistons. Just putting in new pistons and rings will not help because the cylinders have worn too big and honing will only make is worse. They have to actually be bored oversized and larger pistons and rings installed.

I only use Group K for my machine work. Stay away from FullBore and SES if you want to see your engine before next winter.