Mercury Sportjet 90 rebuild or replace?

[summerfun99]

I purchased a used 1994 Searay Searayder during the winter. I recently took it out for a ride, and the power didn?t seem to be right. (Sluggish) but once on plane it seemed to move pretty well. So I decided to take a closer look at the motor (sportjet 90). I checked the compression in the cylinders; top 140psi, mid. 145psi, bottom 5psi.
So now I have a $2000 paper weight in my driveway. It looks like I?ll need to remove the engine to gain access to the head to get a closer look. The boat is in excellent shape for its age, and think it?s worth rebuilding.
Q; is removing the engine going to be a difficult job? What service manual would you recommend? Thanks for the advice, Bob

 

[kenimpzoom]

Re: Mercury Sportjet 90 rebuild or replace?

This boat really isnt a PWC, it is a Mercury outboard engine mounted to a jet drive. I suggest you repost in the Mercury forum. You can find more info on this engine under the Mercury forum.

You can get a manual right here on iboats. You can check ebay for used copies, seach for "sport jet".

I have never pulled my engine myself, but a friend of mine did, and he lifted it out by hand. There are only a few bolts to remove.

Ken

 

[summerfun99]

Re: Mercury Sportjet 90 rebuild or replace?

Thanks Ken, I'll do that. Should I remove it from the jet ski forum?

Bob

 

[kenimpzoom]

Re: Mercury Sportjet 90 rebuild or replace?

Yea, I would suggest posting any future questions in the Mercury engine forum.

Rebuilding these engines is pretty easy if you are good with tools and know stuff about cars.

You might get lucky and find a problem with the rings on the bottom cylinder.

I suggest getting a manual, pulling the engine, and pulling out the bottom piston and then see what you got.

However, I would make quadruple sure that the bottom cylinder is only getting 5 psi. Put your finger over the spark plug and crank engine. How does it feel? You can get a sort of look at the piston by removing the exhaust manifold from the right side of the engine. That is really simple, just unbolt off the 10-20 bolts and then losen the hose clamp from the exhaust. Go slow with the bolts as they are probably corroded and can break if you go to fast. FYI a new exhaust manifuld gasket is 37 bucks.

Ken

 

[Capt Ken]

Re: Mercury Sportjet 90 rebuild or replace?

Actually its a Chryster/Force engine that was used by Mercury. Eight nuts holds the unit down to the jet pump. Simple engine but the crankshaft is different from the standard outboard engine. The splines where it connects to the pump is different.

 

[lilngineer]

Re: Mercury Sportjet 90 rebuild or replace?

Hi Bob,

My name is Jason and I live in the Detroit area; Shelby Twp to be exact. I have just purchased a 1994 Sea Rayder with the Mercury Sport Jet 90 in it. It has a cracked block and damaged piston and needs to be rebuilt.

I saw on the jetboat14 forum that you successfully rebuilt your motor and was wondering if you could share some insight on the topic with me. I tried to register on the site, but I cannot login and the admin does not answer my emails. I just happened to find your profile on here.

I am not a mechanic, but I am a mechanical engineer and tinker in almost everything. Just like you, I am on a small budget and would like to do the rebuild myself. I managed to find another used 90 for replacement parts, but would appreciate in you could share your experiences with me prior to the rebuild. I just figured since we are local to eachother, maybe we can help eachother out from time to time.

If you would be willing, please PM me and let me know.


Thanks a lot,

Jason