Failed Piston

[Carl Schwabe]

I bought my LS2000 last fall and have only had it out three time when this happened. I was told that the now failed engine was replaced once before when I bought it. The cylinder seemed to have plenty of oil on it when I pulled it. Looks like the ring caught on the exhaust port on a down stoke. I did notice the engines did sound different from each other when I bought it, but being new to the whole jet boat thing I did not think anything of it.
So looking back at everything, it may have been showing signs of issues when I bought it.

1. The first time out last fall seemed uneventful except for being hard to start.
2. The second time out two weeks ago, I started in the yard before taking to the water. Seemed like I have to give it allot of throttle to get it to start, once started the both ran good. We stopped to swing ~1 hour and then started up. The port engine stalled several time at idle. After it warmed up it ran ok.
3. The third time out, again both engines seemed like they need allot of throttle to start. They both ran good ~1 hour and again we stopped to swim. When we started the engines up the port engine seemed to be lacking RPM at power with same throttle as the starboard. ~15 min of running the boat the port stalled at power but restarted, several times. We then took it in.

Compression at home was 115, 115 and 30. At that point pulled head and saw chunk out of head. There seemed to be a fair amount of oil on the piston when I pulled it so I do not think it is an oil issue.

I have not found any smoking gun.
I took the cylinder to a local machinist, He only had to take .25 mm off to clean the cylinder up.

I ordered three new oversized pistons.

Anything else I should look at?
I was told I should rebuild/clean the carburetor?
I did run water in the yard with hose to engines with out them running, while starting before I knew better, Could this have caused this issue?

Also where can I find the torque specs for the everything on the engine?
Thanks for any help

 

[DCB-270]

Lack of oil is what usually kill's the two strokes make sure your oil pump and lines are working properly or switch to pre mix.

 

[4x15mph]

I would rebuild the carbs and check that the cooling system (expansion chamber) is cleared. Also, is the engine out of the boat? You will want to make sure you clean out the entire crankcase since there could very well be some metal floating around somewhere

 

[DCB-270]

Could have been a replacement SBT motor. I got one from them on my Exciter. It blew in 1 month. They sent me another under warranty. It blew 1month and one year past original purchase. No more warranty. With the winter months a one year warranty is more 3 to 4 months. Rebuilt it myself (New Yamaha crank and pistons) and ran like a top till I sold.

 

[Carl Schwabe]

Thanks for the feed back. I have everything back together and started it in the yard. Everything seems good. I bought the pistons from PWC engines, The piston kit came with piston, rings, pin and clip. The piston is WSM and the rings are OEM from Yamaha. I am also looking at changing to a Lucas oil two stroke oil. I have always had good luck with Lucas oil product.
Should I drain the old oil out before I add the new brand of oil?
The old owner used Yamalube and this is the first time I have had to put oil in it.

 

[4x15mph]

Great to hear. Did you clean the carbs? Clean the crankcase to make sure there were no pieces left over?

Can you give me an idea of cost for the machine work on the cylinders and the pistons/total job? Thank you and if/when I do a preventative rebuild, I may have questions.

 

[Carl Schwabe]

Everything cleaned up well . I took it out for a break-in run today, Ran mostly at idle and about 30 min at about 1/2 throttle. Now the rebuilt one sounds better than the other. I pulled the plugs and they brownish, maybe a little wet from the oil. I checked the compression before 120 and after 110. I think I had allot of oil in the cylinders on the first check and now all that is burnt off. I would expect the rings to seat better over the next hours of running and the compression should come back up some.
The machine shop charged me $80 to take .25 mm off all three cylinders, which cleaned up the scoring.
The piston kit was $78 for each piston. Of course the new piston size now is 84.25mm

 

[gonzaloak]

I bought my LS2000 last fall and have only had it out three time when this happened. I was told that the now failed engine was replaced once before when I bought it. The cylinder seemed to have plenty of oil on it when I pulled it. Looks like the ring caught on the exhaust port on a down stoke. I did notice the engines did sound different from each other when I bought it, but being new to the whole jet boat thing I did not think anything of it.
So looking back at everything, it may have been showing signs of issues when I bought it.

1. The first time out last fall seemed uneventful except for being hard to start.
2. The second time out two weeks ago, I started in the yard before taking to the water. Seemed like I have to give it allot of throttle to get it to start, once started the both ran good. We stopped to swing ~1 hour and then started up. The port engine stalled several time at idle. After it warmed up it ran ok.
3. The third time out, again both engines seemed like they need allot of throttle to start. They both ran good ~1 hour and again we stopped to swim. When we started the engines up the port engine seemed to be lacking RPM at power with same throttle as the starboard. ~15 min of running the boat the port stalled at power but restarted, several times. We then took it in.

Compression at home was 115, 115 and 30. At that point pulled head and saw chunk out of head. There seemed to be a fair amount of oil on the piston when I pulled it so I do not think it is an oil issue.

I have not found any smoking gun.
I took the cylinder to a local machinist, He only had to take .25 mm off to clean the cylinder up.

I ordered three new oversized pistons.

Anything else I should look at?
I was told I should rebuild/clean the carburetor?
I did run water in the yard with hose to engines with out them running, while starting before I knew better, Could this have caused this issue?

Also where can I find the torque specs for the everything on the engine?
Thanks for any helpView attachment 57729 View attachment 57730

I bought my LS2000 last fall and have only had it out three time when this happened. I was told that the now failed engine was replaced once before when I bought it. The cylinder seemed to have plenty of oil on it when I pulled it. Looks like the ring caught on the exhaust port on a down stoke. I did notice the engines did sound different from each other when I bought it, but being new to the whole jet boat thing I did not think anything of it.
So looking back at everything, it may have been showing signs of issues when I bought it.

1. The first time out last fall seemed uneventful except for being hard to start.
2. The second time out two weeks ago, I started in the yard before taking to the water. Seemed like I have to give it allot of throttle to get it to start, once started the both ran good. We stopped to swing ~1 hour and then started up. The port engine stalled several time at idle. After it warmed up it ran ok.
3. The third time out, again both engines seemed like they need allot of throttle to start. They both ran good ~1 hour and again we stopped to swim. When we started the engines up the port engine seemed to be lacking RPM at power with same throttle as the starboard. ~15 min of running the boat the port stalled at power but restarted, several times. We then took it in.

Compression at home was 115, 115 and 30. At that point pulled head and saw chunk out of head. There seemed to be a fair amount of oil on the piston when I pulled it so I do not think it is an oil issue.

I have not found any smoking gun.
I took the cylinder to a local machinist, He only had to take .25 mm off to clean the cylinder up.

I ordered three new oversized pistons.

Anything else I should look at?
I was told I should rebuild/clean the carburetor?
I did run water in the yard with hose to engines with out them running, while starting before I knew better, Could this have caused this issue?

Also where can I find the torque specs for the everything on the engine?
Thanks for any helpView attachment 57729 View attachment 57730

hi Carl, a bit outdated, but how did you know the right piston specification? Have to replace one, but don’t know if it should be of 0.25mm, 0.5mm or std?