Connecting Rod Question

[mostlyharmless]

Good evening fellow members,
I pulled the pistons from my 787/800 project, and there was discoloration on both the connecting rod small end ID, and on the piston wrist pin (basically looks like the needle bearings cooked the oil and it burnt). This is on the PTO side piston which was the point of failure in this repair. I can probably hit it lightly with scotchbrite and it would come right out. I plan on replacing pistons/rings/pins with the kits that are available from SBT, a light hone on the cylnders(scuffing is extremely minor), clean out crankcase, reassemble lower, assemble upper with new piston kits, new gaskets, and call it a day.
I will include pictures tommorw in the morning. Primarily I am looking for a more experienced opinion then my own.
Thank you to the members for your assistance and insight with my questions. Sincerely Mostly

 

[etemplet]

I use WSM Pistons and top end kit from Bay Area Powersports in Virginia. I'd take some measurements on the cylinders before I ordered pistons. One thing is that WSM pistons recommened (0045") piston to bore clearance so you get a little more leeway on bore size. If you decide to call Bay Area talk to Jason. You should be able to find the pistons you are looking for. Ebay vendors sell WSM and all type of pistons. I don't waste money on the coated ones. Just isn't worth it to me. I'm not recommending that to anyone it is just what I do personally. Good Luck.

 

[tobytd]

New pistons in old worn egg shaped cylinders NOT GOOD.
oversize pistons, bore, hone, chamfer port openings.

 

[mostlyharmless]

Good afternoon Toby,
I was on the same page essentially. There is a decent automotive machine shop that I was going to use to clean the engine. I'm a machinist but totally different level than automotive.
Was curious if it would be more reliable in the long run if I had it re-sleeved, then bored and honed to standard dimentions. Also if the existing sleeves get bored oversize, than the remaining thickness, being thinner, would be prone to running hotter? With the ski being that old(1996), there may be fatigue issues present in the steel, which could be an issue as soon as next season.
I got this ski for my girl and the safety/reliability considerations come first. Just don't want any issues that could sour her on boating, and it sucks to break down on the water.
I greatly appreciate your insight Toby and would like to hear your thoughts regarding the boring of the old sleeves, or going with fresh, back to spec sleeves.
I included pictures of the rod, small end, that concerns me.
Thanks again Toby.

 

[mostlyharmless]

Was going to see if scotchbright may clean the rod up

 

[JC-SUPERJET]

Those Rods and Pins are shot.

An Automotive Shop will most likely NOT Chamfer the Ports after the Bore and Hone. Use a 2 Stroke Shop, Jetski, Motorcycle or Snowmobile, who know how to Bore & Hone 2 Stroke Cylinders..

No Chamfer on a New Bore will eat the Piston Rings.

You need a full engine rebuild, unless you know how to rebuild Crankshafts...

 

[mikidymac]

Yes, as said above rods/crank are toast.

No, boring cylinders oversized does not reduce reliability or cooling at all. Bore yours oversized and fit new oversized pistons. Do it correct or you will just be doing it again.

 

[burtshaver2021]

Just trying to grab a few pointers for future projects, what is it that you see that tells you the rods and crank are done?

 

[mostlyharmless]

In the connecting rod small end is scoring and very mild dimples where the needle bearing pins were located.
Although there was free movement of the pistons themselves, the wrist pins were kinda tight(this movement was only checked by hand). I would guess that conditions under load would be much more demanding and any hang up, excessive movement, or misalignment of the piston while running would be catastrophic.
I am going with a rebuilt crank from PWC. My question however to the group concerns fitment. Would a crank from a 96 XP 787/800 be compatible with a 96 GTX 787/800? Will it transfer right into my existing case and match the balancing shaft I already have? Should I only source a crank with a matching balance shaft? I am just curious. I will call the supplier today to nail all this down, but I am guessing that a seadoo rebuild is similar to any other crank rebuild which would include a grinding of the main bearing surfaces and using a matched race in the assembled engine. Again, just a guess.
Also, removing the PTO flywheel using the splined tool isn't working. I made up a MAG side flywheel holder similar to the one that the service manual depicts, but I can't seem to get the leverage I need. Since I need to send in my current crank as a Core, I was going to split the lower end, and grip the crank in a suitable vise bolted to a large metal workbench. So far, with mercruiser outdrives at least, using this particular vise, the outdrives lost and surrendered quietly. Hopefully I can say the same for seadoo. I will keep the group posted.

 

[mikidymac]

All 787 carb cranks are interchangeable.
It is always a good idea to rebuild the balancer shaft with a new crank.

 

[mostlyharmless]

I have decided to go with a SBT rebuild with warranty rather then hodgepodge it

 

[mostlyharmless]

This was suggested by the engine builder doing my 5.0L Mercruisers

 

[mikidymac]

I have decided to go with a SBT rebuild with warranty rather then hodgepodge it

All I can say is good luck. They typically make it just outside the warranty and that is about it.
Make sure you service the fuel system before any new engine is started.

 

[mostlyharmless]

I will do just that, thank you for the tip mikidy. Depending on cash flow when I'm ready, I might go with a premium engine that comes with a 2 yr warranty. It gives peace of mind, saves me from the time spent in labor of changing it again, and if it fails early, I'm covered by the warranty.

 

[mikidymac]

Just keep in mind that it is the exact same engine. You are only buying an extended warranty with the "Premium" engine. You still have to pay the labor and shipping both ways out of pocket.

 

[mostlyharmless]

Since I have to align the engine I am going to rebuild the jet pump using the sbt rebuild kit. The service manual calls for the seadoo only reccomended gear oil for this rebuild/maintenance task.
Is there any difference from a standard high performance gear lube like I would use in an Alpha1 MerCruiser lower unit?
As always, thanks for the experience and insight from the members here.
Mostly

 

[tobytd]

Full synthetic, 75/90 gear lube….any brand will work.

 

[Hudson 1975]

Welcome here