97 Seadoo XP 787 Damaged Piston and Head

[Welder75901]

I recently was given a 1997 Seadoo XP with the 787 engine. I knew it did not run but from the information I recieved from the owner it only needed a good carb cleaning, and fuel lines changed. Once I finnished the carb cleaning, I tried starting it. Not my first time doing this on a Seadoo. Engine would start and die. After some trouble shooting I tested the compression. Rear cylinder was good at 160psi, front cylinder however barely moved the needle. Pulled the heads off and found what I would call a severly damaged piston. Pictures provided. Should I replace both just because I'm in the unit, or will the rear piston be ok as is? Also any thoughts as to why this happened. I feel like the severly clogged carbs probably had something to do with it, but I'm not for sure. Don't want to rebuild it to find out something else caused it. Also where would be the best place to purchase the parts for it.

I would appreciate any advice or thoughts on this.

 

[Axkiker]

I was in a somewhat similar situation recently and after advice from many on here decided to tear the entire motor apart and rebuild. I fought the idea of tearing it completly down as my bottom end turned freely and showed no signs of damage. However after tearing it apart I easily see how metal fragments from the piston or rings could have gotten into the bearings and destroyed the entire thing. I pulled mine apart and didnt find metal but did find a bunch of gunk which needed to be removed. If there had been metal fragments in there I would never have known it. I would have put a new top end on the thing, ran it for several hours only to have it melt down shortly after.

I was able to reuse my crank and have the peace of mind to know its clean and all bearings are good to go. Plus tearing it down and reassembling is really not that big of a deal in my book. the hardest part is figuring out the steps, tq spec etc etc.

 

[Welder75901]

I appreciate the advice. I have been trying to decide if it would be best to just rebuild the whole engine. Probably what I will do. Nice winter project, but waiting to test it will drive me nuts.

 

[Axkiker]

I appreciate the advice. I have been trying to decide if it would be best to just rebuild the whole engine. Probably what I will do. Nice winter project, but waiting to test it will drive me nuts.

Honestly tearing it completely down will not take you much more time. The bottom end to be is easier to assemble than the top end. If you are gonna go to the trouble of pulling everything off the top the bottom is a piece of cake

 

[68ragtop]

You almost have to pull it all apart IMO. Not only to see how the rest of it is, but like mentioned above, You gotta clean it out.
Its insurance on your investment. Good chance some of those fragments are still in the basement..... Even if you do a fantastic job on the top end, all it takes in one left over piece downstairs & it will be upstairs soon after startup & you will be doing it over again.
Just my $.02

 

[Welder75901]

I know what I'll be doing, complete rebuild on a 787.

So where would be a good reasonable place to buy the parts?

What items through out would be smart to replace even if still good?

I plan to replace both pistons, should I hone the cylinders for good measure?

Last am I correct in my thoughts of what caused this to happen. Clogged carb, and run lean to long.

 

[Jeffspx]

Looking at the head, it either looks like it ran lean for a while and burned up, is there pieces of the piston in the cylinder? Another possibility is if one ofthe butterfly screws got sucked into the motor and bounced around the cylinder. Probably the first, but in any case, I'd pull the motor and tear it down, not only do you get the piece of mind cleaning and inspecting internals actually seeing and knowing what is good or not, but you'll get the chance to clean the inside of the hull under the motor and paint you motor, if it's peeling like mine. You'll also get to inspect rotary valve clearance and timing, and inspect the timing components.
Good luck

 

[Axkiker]

I purchased all my stuff from Bay Area Powersports, Bayareapowersports.com. I found them selling on ebay along with several other vendors. They were the only people to actually answer the phone and talk with me. I ended up with an entire top end kit, (2 pistons .5mm over, rings, wrist pins, bearings, and an entire engine gasket kit) all for 230.00 shipped. It was by far the least expensive option I could find. Not to mention THEY ACTUALLY SPOKE WITH ME. I cant even get one of the largest parts suppliers in my city to answer the phone. When someone does its only to put you on hold. Anyways I have my motor almost complete and so far have not had the first problem with the parts I ordered from them. I even needed to order an additional part which i tried to find in town but was unable. Once again the only people to answer the phone and talk with me was Bay Area Powersports. They found the part and had it drop shipped to my home...

 

[Welder75901]

Thanks guy's. One more question, I think I should also replace the cylinder cap that is also damaged. From the pictures would you agree?

 

[Axkiker]

Thanks guy's. One more question, I think I should also replace the cylinder cap that is also damaged. From the pictures would you agree?

If by cap you mean head I would guess its a good idea. I have seen some use die grinders to smooth out the nicks but im not sure how that affects the performance or reliability.

I know sharp edges in an automotive combustion chamber are a big no no as they lead to premature detination.


Im a novice so hopefully someone with more experience will chime in.

 

[Minnetonka4me]

That head is pretty nasty...a few dings is ok but that thing is hashed.


I have mint heads for $80 shipped as well as any other 97 XP part you may need.

 

[Welder75901]

Good to know you have the parts. I will get back with you on the head, I'm gonna have to replace it for sure.