RIP: 1200STXR ate the connecting rod Crank Bearing

[Mikes1200STXR]

Well it was a short lived season. I spent the last couple months rebuilding this ski, fixing small issues here and there. On a ride last week, it decided to eat the #1 connecting rod bearing. Ski was behaving normally, and it seemed to happen at WOT at 55mph-ish. All of a sudden lost power, slowly slowed down, and wouldn't restart. In removing the head, it sucked up the bearing and smashed it between the piston, head, and cylinder jug. The jug is scored badly and I will need a replacement, as is the head.

I'm curious as to the cause...the ski did sit for 2 years before I got it. 150hours on the ski. I theorize that some rust or debris cause that bearing to fail. Carbs were gone through recently and were squeaky clean. The oil lines were all replaced and are functioning normally. I even ran premix with the oil lines, although probably at 75:1 vs 50:1. From what I read, if there was an oiling issue, the pistons will give up well before the bearings do.

The other cylinders and pistons look and feel perfect. I will have the engine rebuilt as I still enjoy the ski, and the price I paid makes it worth it to keep. Any ideas on the reason for the failure?

[Mikes1200STXR]

Today I took apart all of the carbs (again) to make sure they were functioning correctly. The fuel sitting in the carbs looked premixed. I sprayed carb cleaner through the oil injection passages, all were clear. When I put tubing on them and try to blow through them, I get a lot of resistance before I can get air to go through. All three are like this so I believe those are the check valves working. I will double check the oil injection pump again, but all of the lines are full of oil. I do not think this was an oil injection issue, unless its something that happened for a few minutes and then went away.

I have a small rubber syringe in the shop and was able to easily pump oil through the passages, simulating the oil injection system.

I should note, I did not have any warning lights during this whole ordeal. A single piston overheating slightly might not be enough to cause an overheat alarm, especially if the water injection is functioning correctly. Ill have to defer to someone with more knowledge than I have.;
.

[steve45]

Bummer!

You are lucky that you didn't blow a hole through the bottom of the crankcase (assuming that you've inspected it).

The only way to check the pop-off valves is with a pressure gauge. They should open at about 4-5 PSI, which is more than you can blow through them. If you have a pop-off tester for carbs, you can use that (you may have to put on a different gauge).

So is it the large rod bearing that failed, or the wrist pin bearing? I can't see the crank end bearing very well in your picture, but it looks like the rod got hot. Usually if the crank end fails, the rod breaks and cuts the engine in half.

Keep in mind that pumping oil through the oil passages doesn't simulate the oil injection system, as much of the oil flows into the carbs and gets mixed with the fuel/air mixture that goes through the reeds and into the crankcase as vapor. If you carb gets plugged up, you do not get fuel nor oil from it. This is why I don't recommend converting engines to pre-mix. People think it's foolproof, it isn't. On my Ultra 150 (same engine), I converted to the Yamaha injection design using external inline pop-off valves and injecting the oil directly into the carb throats. That way, if the carb gets plugged, you still get oil even if you don't get fuel.

When you opened the carbs, did you check the internal filters? Check the pop-off pressure? Clean the fuel rails and replace the O-rings on the fuel rails and needle valves?

[smokeysevin]

If you end up needing cylinders let me know, I have a few left.

Sean

[Mikes1200STXR]

Thanks all. I did not check the pop off pressure, I will have to try that. I changed all gaskets in the carbs, cleaned the internal filters, replaced the needle valve seals...everything looked squeaky clean too.

To clarify, I pumped oil through the inlet passages on the carbs...to where it would mix with the fuel...seemed to work fine. In testing the ski, I checked periodically the temp on the water outlet, all seemed OK.

It was the large end that broke. I do not think that the case was damaged, I still have to pull it out to inspect. Do you have instructions on how to convert to the Yamaha style system?

I picked up a spare engine to repair mine with a rebuild. My plan after rebuild, going forward, was to just run 50:1 premix and keep the oil injection system active as well.

[steve45]

No, I haven't written anything on it yet, but this is the same thing. This is actually a primer line on my Ultra 150, but you can add the oil lines the same way. I drilled 1/8" holes and inserted 1/8" brass tubing to get the oil inside the carb throat. I put some red LocTite on the brass tubing to make sure it didn't come out of the carb. Be sure to check for clearance between the tube and the choke plate. I cut the oil lines and installed the Yamaha check (pop-off) valves. Make sure the arrows on the valves point toward the carbs. You'd better be sitting down when you see the price of those Yamaha valves!

I'd run pre-mix for a while until you verify that the system works and any air bubbles have worked their way through the system.

[Mikes1200STXR]

So the rationale here is that the external check/pop off valve is more reliable than the internal one, and since it is in the throat instead of the body, it should always be getting oil even if there is a problem with the carb fueling?

[steve45]

Not quite. I don't know which valve is more reliable. I've seen both fail and they all failed open, which provides oil flow. One of the most common carb problems is plugging of the internal filter. When this happens you don't get gas flow or oil flow. The discharge ports in the carb throat are very small. The ID of 1/8" tubing is about 3/32", which is huge in comparison to the ports. They won't get plugged up and completely bypasses the internal passages of the carb. You do have to plug off the old nipples for the original system.

[Mikes1200STXR]

I might just verify the pop off pressure on each, and run premix and the oil injection.

I know its not 100% guaranteed as a fail safe, but I think it gets you damn close.