Seadoo XPL 951 Piston Scoring on rebuilt engine

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WaterJet

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Hi all,

I recently purchased a 1998 Seadoo XPL, it presents like new and the engine was rebuilt apparently with less than one hour of use on it. I’ve now put over 2 tanks of fuel through it breaking in the engine and started riding hard for the last 30 mins of riding before a rave valve spring slipping off the bellow was reducing the rpm because the valves couldn’t open.

After removing the raves I notice some potentially bad scoring on the pistons. What do you think of this?

I’m worried it could be because I’m riding in 10-12C water (50-54f).

What do you think?
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This is what the rave valves look like. Looks like they have been ground back to accomodate for the .25mm overbore. Could they possibly be hitting the pistons?
 

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Only 3 hours run time !!! Man one of those pictures looks pretty bad. Yikes. bummer. What was the piston clearance and what the hey is all that oil doing in there? Pull it apart but looks like you'll need a rebore. I run WSM pistons and they need a little extra clearance. I take my time warming the up before riding and am very anal about that. Usually 5 minutes or so idle or just off idle. Hope you have some good news on this when you get it apart.
 
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It does suck but at least it’s winter in Australia so there’s time to get it sorted out! The guy I got it off did the rebuild, so I don’t know a lot about the engine. It might be the 2nd rebuild because the raves are shaved back a fair bit.

The oil pump is definitely working, and I also ran some premix in the first tank, that might be why the raves were covered in oil.

I’ll start tearing it down and post what I find!
 
Got the head off. There’s probably 1mm of movement between the piston and cyclinder when pushing the top of the pistons side to side. Could the pistons being too loose in the cylinder cause this scoring? I didn’t notice any bad sounds from the engine and it ran really well pushing 6900rpm before the rave valve bellow have problems.

I’m sure the oil pump was working. There was smoke noticeable out the exhaust and the oil tank dropped in level on the ride. Thoughts?
 

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Here are a few more photos. There is a gouge in the mag cyl, is the cylinder still ok to use since it’s below the rings?

You can also see the intake side of the pistons, I don’t understand how it didn’t seize, was still pushing 6.9k rpm before pulling it out. It all feels very dry. Maybe lubrication was a problem. At least the bottom end feels solid. Any tips on where to go from here are greatly appreciated!!
 

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I am sure the bore was not done correctly or the clearances setup to spec. It also looks like he didn't chamfer the ports at all so that again is bad.

If it was me I would take it to an actual machine shop that does 2-stroke engines and have them measure everything and fit new oversized pistons with the correct setup clearances.
 
947 engine likes lot of clearence, if i remember 0,12mm min. piston to wall, without measuring to me that doesnt look like excessive clearence
 
Just make sure the bottom end is clean. Check connecting rod for excessive movement on the crank.. push/pull. You shouldn't feel any movement. Look for particles. If this engine has an oil channel that holds 1. oz of 30wt... make sure you check it and add what is necessary.
 
Thanks for the pointers guys. Good to hear the piston clearance doesn’t look too bad in the video, this gives me more confidence the bottom end was done right. It does have ProX con rods. Definitely feels like it’s smooth and no play. I’ve found a local shop that can bore the cylinders and I’m now waiting for the 1mm oversized Sbt top end kit to arrive.

Thoughts on the SBT engine parts?

I’ve decided to convert to premix, so I got an oil pump block off plate too, the lubrication was definitely the problem based off how dry it all was. I’m still not sure how because it was definitely using oil the ride before I took off premix. I’ll have to look into how it gave in a bit more.
 
Don't put SBT pistons, Buy OEM, PRox, or WSM Platinum, if it was my engine i would buy Prox pistons, and piston to wall clearence 0,13mm, 0.12mm piston to wall is the minimum, i would say 0.13mm and Prox piston
 
Looking Better to your piston pictures i would say that engine injested water, the scuffing is on the intake and exhaust side right? what piston brand do you have ?
 
I’ve already ordered SBT pistons lol. What’s not good about them?

I’m not sure what brand, but because they put in ProX rods I’d assume they’re ProX pistons.

Yep scoring is on both ex and intake. The intake sides have much worse scoring. There was no rust anywhere and no water in crank case...
 
Sbt and Wsm are inferior pistons to OEM or Prox, Prox Pistons are made by ART a japanese piston manufacturer, many honda, yamaha and toyota uses ART pistons, they are the top brand of recreational vehicle pistons, WSM platinum pistons looks good, never used them, you dont need to have water in the crank, just some water ingestion through intake, the Xp limited are known to ingest water easy.
Buy new gasket's, go to a good machine shop, cut the rave valves, chamfer your transfer ports, torque all the bolts correctly, download the manual, and follow the manual.

Best Regards
Daniel Pinto.
 
Just got the new top end kit today.

With the piston to cylinder wall clearance should I go off the service manual, or the manual that came with the pistons.

The seadoo service manual recommends a
.0035” clearance minimum, and a .008” wear limit.

The SBT manual recommends .007”-.008” clearance.

Thanks again for the help.
 

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In my opinion, SBT put those clearences to reduce the chance of a cold seizure and less warranty's, if it was my engine i would put 0.12 / 0.13mm piston to wall, i think later 947 have more clearence on specs, let me find out
 
Haha this will be a tough decision. Are these engines prone to piston slap if the clearance is too much?
 
Haha this will be a tough decision. Are these engines prone to piston slap if the clearance is too much?
947 engines make some piston slap, with the clearences that SBT whants, you Will have to much piston ring Gap, and to many piston to wall, blow by, and bad Colling because the piston barely touchs the cylinder wall
 
Well, I guess I’ll make sure they aim for .007” clearance, I’d hate to get a cold seizure as I ride a bit in cold water around 50-55f. On the strokes the piston will still be in contact with the cylinder wall from the sideward forces I would think?
 
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