OMC 115 Turbojet Bad Piston Replacement Help Needed!

[Bigredmachine878]

I’ve got a 94 Four Winns Fling with an OMC 115 Turbojet that I’ve suspected had issues after buying this summer. The 115 is traditionally an outboard, but mounted inboard for the turbojet variation. I noticed the motor seemed sluggish and it seized up after doing a hose flush after pulling it out last. Tearing into it revealed a damaged piston with a missing ring and a cracked thermostat housing. Looks like the thermostat housing crack led to the piston overheating, but not sure where the water got into the motor. Bad piston still tests at 100 psi, but is missing a ring.
I’m new to tearing into motors, so I’m hesitant to pull the entire motor and do a total rebuild. Is it possible to replace the piston without pulling the motor? My research shows that removing the intake manifold, crank cover, and cylinder head will allow me to remove the piston, but I’ve read posts saying the entire powerhead needs removed. I don’t know if its possible to do with the motor is still inside the boat. The cylinder wall of the bad piston looks decent enough and the other 3 cylinders look good. The boat is in great shape and the motor ran, although sluggish, so I’m trying not to get too crazy with it. My wife thinks it was fine until I rebuilt the carbs . Any advice?

 

[flyingscott]

Those motors are known for breaking the rings it is very common in the crossflow motors. That motor needs to be bored out and 4 new pistons put in it. Because if 1 breaks the other pistons are not far behind. Pull the motor and do it correctly.

 

[racerone]

There you go.----A most common failure.----Pull the motor out !

 

[tphoyt]

Yea there are not short cuts here.
Do it right or do it again.

 

[racerone]

You need 4 new pistons.----At least 1 cylinder bored.------Pick some new pistons that do not have the wild taper ( design mistake ) on the top ring.

 

[Bigredmachine878]

Is there a way to remove the powerhead without taking the adapter plate and muffler out? Not looking for any shortcuts, just gun shy about the whole thing.

 

[racerone]

Well----I removed an engine from one of these a few years ago.----Broken piston rings !-----You guessed it , the adapter has to come out with engine on it.

 

[flyingscott]

Buy a factory manual for your motor. It will have information and instructions for that model.

 

[Bigredmachine878]

Well----I removed an engine from one of these a few years ago.----Broken piston rings !-----You guessed it , the adapter has to come out with engine on it.

Looks like a tight squeeze to get it out, but I’m sure there’s a way

 

[racerone]

nothing to it

 

[Bigredmachine878]

Buy a factory manual for your motor. It will have information and instructions for that model.

I’ve got one and its been a huge help!

 

[racerone]

These jets boats were marketed for about 4 years.----As is typical everybody that wanted or had one got tired of them.-----Production numbers dropped after those first years.-----Many of the Turbo Jets suffered broken rings.----Might have to do with the nature of operation of jet boats.----Constantly going from idle to full throttle and back to idle again.

 

[Bigredmachine878]

These jets boats were marketed for about 4 years.----As is typical everybody that wanted or had one got tired of them.-----Production numbers dropped after those first years.-----Many of the Turbo Jets suffered broken rings.----Might have to do with the nature of operation of jet boats.----Constantly going from idle to full throttle and back to idle again.

Its definitely an interesting boat, which is what drew me to it. I’d prefer something that can be kept in my garage so options are limited between something like this or a 70s tri-hull. My brother and I rented (and about sunk) a tiny sea-doo jet in disney world back in high school so I always thought it would be fun to own something similar.

 

[Jon NL]

Hi I also have a mid 90's fourwinns fling with motor problems requiring the motor to be pulled out, interested in the procedure for doing so