2001 Polaris Virage Bad Piston

[Bluedmax]

I discovered a problem with my 2001 Polaris Virage last week. It's been running good this summer with the exception of an occasional "misfire" that I haven't pin pointed yet. Every once in a while one of the cylinders would cut in and out quickly like an electrical issue, mostly when cold. Then last week, one cylinder stopped firing all together. I pulled to shore to start trouble shooting and found the tip and electrode of the front spark plug smashed closed. I re-gapped the plug and it ran fine back to dock. Once home I used my small endoscope camera down through the spark plug hole and found significant damage to the front piston and ring. I attached some pics labeled "front" to illustrate. It looks like it's been a problem for a while based on how bad it is. What I can't believe is how good it's still running. When I checked the rear cylinder, everything is shiny and new looking (is this too clean??). There's 2 labeled "rear". Before I tear it apart, is there anything I should troubleshoot first to see if I can identify what may have caused this while I can still run the engine? I don't want to repair or replace the engine, only to have the same problem occur again because of something else not working correctly. For what it's worth, my dad bought the ski brand new and the motor has never been apart. Everything is bone stock. I rebuilt the stock carburetor about 2-3 years ago and just rebuilt the jet this last winter.
Any ideas what may have caused this or anything I should check before tearing into it?
-Carb adjustment?
-Oil system?
-Leaky gaskets / seals?
-other?

Then I'll need some direction on how to repair...
-1 piston / cylinder?
-complete top end kit?
-replace the whole engine?

Thanks in advance!

[randys]

until you pull the cylinder head and look at the walls its all a guess. you might be able to get away with a hone and a new piston if the walls are not too bad.

I had similar but with an added hole in the center of the piston. I ended up having to replace a whole jug assembly myself. There was a lot of aluminum debris in the crankcase and intake ports behind the reed valves and I cleaned it out as good as possible.

as far as what caused it, could be several things. carb lean, intake leaks, bad reed valve, spark plug heat range, crankcase leaks, or just a bad piston. Will just have to tear into it and figure out

Then I'll need some direction on how to repair...
-1 piston / cylinder?
-complete top end kit?
-replace the whole engine?

Thanks in advance!

[Bluedmax]

Thanks for the reply, sorry to hear you burned one too. Yeah I should know a little more about the extent of the damage once I get things pulled apart.

My first thought is if I can do any useful trouble shooting while it still runs, before tearing into it... like spraying some chemtool around different areas to check for leaks. I know that will work on carb and intake areas. Would that reveal crankcase leaks?

If it's a lean condition with the carburetor, wouldn't both cylinders be affected equally?
Is there 1 reed valve the feeds both cylinders, or 2 valves... one for each cylinder?
The spark plugs are factory NGK.

[Bluedmax]

So I got the bad cylinder torn apart. Obviously the piston and inside the head around the spark plug are toast. I'm surprised how clean the cylinder walls are for this much damage to the piston and top ring though. I'd say there's one area on the cylinder wall below the ports with a slight groove. Above the ports the cylinder walls seem very clean and smooth. The 2 pics of the piston show each side, indicating no signs of excessive heat or burn marks. This takes me back to the question... what caused the failure??

There's lots of debris in the areas of the intake and crank as illustrated with my red circles. I'm sure the bottom end is quite contaminated with aluminum, but it's hard to see in there. I moved the connecting rod around on the crank to check the needle bearing play, but not sure how much movement it's supposed to have. I'm guessing there's also a good chance for aluminum debris to be in the needle bearings also? So what now? Do I try to clean / flush the bottom end somehow and rebuild the top end? Do I just replace the whole motor? By the way, anyone know how many hours a good life on a 2 stroke jetski should be? I'm at a bit over 400.

[Bluedmax]

Can anyone provide me some direction as to what I should be looking for next? I'm not familiar with how to inspect the bottom end and bearings of a 2 stroke. Just trying to decide if I can clean it up and just to a top end kit, or if I should be looking at a complete replacement engine.

[radio-active]

NOT an expert, but 400 hours seems like a really good run. But you are playing with fire if you don't take apart that entire motor -- especially since you can see metal down in the bottom.

When my center cylinder went south, I pulled the jug and found the bottom end as clean as could be. I didn't go any further. I replaced that jug, piston, ring, head, etc, didn't touch the rest. 30 hours on that rework and it seems healthy. I think I got very lucky that no metal got down there, but my piston damage wasn't near as bad as yours. In my case I blamed the problem on a spark plug grenading.

[Bluedmax]

I was planning on disassembling the complete motor to inspect and clean everything, which I agree is the right thing to do. But if the crankcase is contaminated and the rotating assembly is worn, I might be better off with a replacement engine.

Does anyone have experience with SBT? It looks like they have everything from top end kits and rotating assemblies (if I want to rebuild myself), or they also have two options for complete engines for $850 and $1200 (freight to ship the new engine and return my core might be a couple hundred each though). They appear to be about the only option that supplies Polaris PWC parts but seem to be reasonably priced. Any experiences with either internal parts or complete engines from them?

The only part I couldn't find if I were to rebuild my existing engine is the head cap. Anyone know if those are available new or would I have to try and find a good used replacement?

[Bluedmax]

I confirmed there's quite a bit of debris in the crankcase. I also checked for play with the connecting rod bearing at the crank. I can see and feel a very slight movement when applying up and down pressure (the direction of piston travel). It's my understanding there should be none this direction. Could someone confirm this please?

Does anyone have experience with the replacement motors from SBT? Given the small difference in cost between sourcing all the individual parts I'll need vs just ordering a complete engine, I think I'm just going to order an engine.

[radio-active]

Generally with any engine there should be no, or almost no play in the connecting rods in the direction of piston travel. There can be some side to side, every design is different. However even new in spec bearings will have a mil or two of play. If you can feel it, it's probably too much.

I have no experience with the SBT engines but if you do a search within the forums, you will see some commenters that appear to not think too highly of them.... Your mileage may vary....

[Bluedmax]

Any other suggestions besides SBT?

[sdlvx]

Wiseco/cometic for gaskets, WSM for pistons. People hate on SBT, their reman engines seem to be the biggest problem with mechanics doing things wrong. Their parts seem alright, not OEM quality but if it's between SBT or nothing, I am grateful for what SBT does.

Would I use a rebuilt SBT crank? No. Would I use their connecting rods? Yes.

[Bluedmax]

The entire engine will need to be gone through due to all the debris everywhere from the piston. Based on the slight end play I have with the connecting rod at the crank, I'm thinking I'll need bottom end parts as well. I'm not sure how to check if the crank is worn, or if just the bearing can be replaced and reuse the same crank?

I'm looking at 2 choices...
1) Try and source all "good" parts and rebuild my existing engine myself (which appears to be more expensive). If I need a reman crank, where can I source that from? SBT offers a complete rotating assembly for $350, but if their machine work isn't good, it's no better than a complete engine.
2) Take my chances on a complete engine exchange from SBT. I would have thought this was the smart way to go... all new / reman / good parts, assembled by a shop that does this for a living, 1 year warranty, I don't mess with all the hassle of going through an engine myself. But now that I'm being cautioned against it, I don't know what to do.

Other than a few suppliers for top end parts only, its seems SBT is still the only option?

[sdlvx]

Crankworks in AZ or Northern Crankshaft in MN, ship whatever is closest, or call around. You can find people who will do it local so you don't have to risk shipping it. Search for machine shops.

[Bluedmax]

I've been asking everyone I know and calling around, haven't been able to find anyone who works on multiple cylinder 2 strokes.

I'm in CA so I'll give that Crankworks in AZ a call.

[Bluedmax]

I need to verify my specific engine model by getting to the stator and checking the size of one of the bolts. I believe I need to remove the flywheel assembly which will require removing the large center nut and using a puller that threads into the 3 threaded holes right?