Seadoo XP Scoured Piston. What caused it?

[seadoodle]

Hello everyone, I just recently picked up a 1992 seadoo xp for $140 bucks. I bought it knowing that there was low compression in one of the cylinders. This is my first PWC and my first big mechanical project. So here is what I found upon inspection
-One cylinder read 150psi while the other read 30
-Took the head off to find the 30psi cylinder piston with a penny sized chip in it (looked like a hole was being created)
-Took the jug off to further inspect the piston and cylinder
-Cylinder had vertical streaks and some scratches
-Piston rings were basically welded to the piston

Other observations about the seadoo
-The bad piston crown was black (blowby probably)
-Both pistons were .50mm oversized
-the other piston was flawless. Cylinder still had it's cross hatches
-Oil covered the bottom of the engine bay (possible fuel injection issue).

Armed with this knowledge, I gathered 3 possible explanations. Air/vaccum leak somewhere, carb too lean, or the oil injection is goofed up.

I have uploaded some images for you to look at

If it was an oil issue, wouldn't the cylinder be basically nuked?
Do I need to re-bore or hone the cylinder?
Where should I spray carb cleaner to test for air leaks?
What's the deal with the almost hole?

Thank you and hopefully I'm making sense to you.

 

[mikidymac]

Whatever cylinder is shot it’s from a dirty carb running it lean.

 

[etemplet]

Mine was pretty bad and cleaned up acceptably enough for me without a rebore. Give the hone a try. Good Luck !!

 

[seadoodle]

Thanks for the help guys! I do plan on checking the carbs, but would it be worth the time to do a leak down test since the muffler and carbs will be off of it?

 

[seadoodle]

Mine was pretty bad and cleaned up acceptably enough for me without a rebore. Give the hone a try. Good Luck !!

What was the honing tool you use?

 

[racerxxx]

You need a ball hone. Flex hone is the company. You can order direct or online retailers. I recently bought a few from Amazon. I believe you want 320 grit. Possible a blue ink marking on the stem.

 

[Chester]

Long, deep grooves on the piston are from water ingestion. The detonation damage on the top of the piston is from running lean. Make sure you replace the crankshaft seals too. Also, it looks like you will have to bore it out.

Chester

 

[etemplet]

What was the honing tool you use?

I am an old machinist. I use an adjustable hone where you can replace the stones and guides for the application. You don't need anything like I have. Of course, I've never used anything else.