HELP, I Blew a piston after rebuilding carbs

[kirkland]

Ok after replacing all the lines and rebuilding the carbs replacing all the gaskets in the whole engine, I have taken thing apart completly several times now been dealing with this since august, I found all the black crap in everything, cleaned it all changed the lines, rebuilt the carbs adjusted the carbs to specs, low 1.5 turns out, high 0, took it out today and I will say the head gasket was one that was installed once and removed and put back on...since it is metal I figured it would be ok, it looked fine. Anyway it got up to 60 for about 1 min or 2 then shut down and wouldn't even want to turn over making a bad noise, had to paddle back. Took it apart and I blew the back piston and there was some water in the front. The back looked like the oil was washed out the front had oil in it but the plug was real bad crusted black stuff burnt on, some small chunks of piston stuck in the head and you can see where the pieces are missing from the top of the piston, I'm going to do a top end rebuild but I want to know how to find out what made this happen. I know I overheated it before I rebuilt the carbs and wonder if it could have been just waiting to get to a high rpm before it let me know. I saw the pistons before this happend after it overheated the first time and they looked fine and it ran fine on the trailer the plugs looked ok with nice oil on them and everything. The thing only has 160 hours it's a 2000 gtx 3 seater with a 951cc 2 stroke. Does anyone have any idea what may have happend and after I rebuild the top end how do I check to make sure something is not still wrong with it........what's the best way to make sure both pistons are getting plenty of oil, not too much fuel that kind of stuff to keep from burning up something else.....also it never sounded the overheating beep it just quit on the spot. I hope nothing is wrong with the bottom end. Thank you for any help, my first seadoo and it's driving me crazy.

 

[kirkland]

Switching to pre mix???

I've heard a lot of talk about it, is it any better for the engine or will it help prevent a blow out?

 

[kustomkarl]

If you have pieces of piston stuck in the head and a hole in the piston chances are you need to pull the engine and check the crank. The pieces more than likely did damage to the bottom end. If it over heated before, and you just replaced the bad parts, it isn't enough till you find out what the problem is. It sounds like now you need to pull it and do a complete tear down to find out all the damage. You might end up replacing the engine if you have crank problems. It is cheaper to go with a recondition engine then try to rebuild it sometimes, depending on how bad the damage is.

Karl

 

[kirkland]

I did pull the cylinder and the bearing at crankshaft is shot in the back piston.

Hey, thanks for the reply, I just got it apart and my back bearings are shot and the piston got burnt up, my real question is why, it was running good had a good engine and everything just had carb problems and old fuel lines so I changed all them and rebuilt the carbs all of a sudden when I get it in the water to check it it's like no oil got to one cylinder or something...not sure what happened but the back cylinder was super clean compared to the front like it only had gas and no oil but the oil lines are all good and it wasn't doing this before the carb rebuild, I don't know but I plan on finding out and fixing before spring, reason I wonder about premix is maybe this wont happen once changed to premix, I still don't know the cause of the one piston and bearing meltdown...(any ideas!)....possible causes........Thanks.

 

[kirkland]

Overheating before was a water hose that came off.

If you have pieces of piston stuck in the head and a hole in the piston chances are you need to pull the engine and check the crank. The pieces more than likely did damage to the bottom end. If it over heated before, and you just replaced the bad parts, it isn't enough till you find out what the problem is. It sounds like now you need to pull it and do a complete tear down to find out all the damage. You might end up replacing the engine if you have crank problems. It is cheaper to go with a recondition engine then try to rebuild it sometimes, depending on how bad the damage is.

Karl

The overheating was from a water hose that came off the first time...at that time it may have weakened some parts and I didn't know it but it has never cleaned the cylinder head and piston down to the metal like it did this time almost like no oil got to the back cylinder, I'm at the end of my rope with this thing but it will be fixed by spring one way or the other, thanks for all the help.

 

[mudpie]

me thinks it was a grenade with the pin pulled.
the time you ran it would not be enough to cause your failure
this motor was probaly on its way out before hand
running with the coolant line off didnt help
this would have cooked the motor, maybe turned the nice silver colour gold?
also this loose line could have put enough water in the hull that the engine sucked a bit in, you cant compress a liquid !!!
add in the fact that the carbs were crudded up,before this happened, this will make the boat run lean, lean condtion makes em run really good on the top end, but makes em run really hot, not good!!!
skis live a hard life, rode hard ,put away wet, sit most of the time, sigh!
as karl stated, a rebuilt motor is the best bet
hate for you to put all that money into the top end, for the bottom end to fail and trash all them new parts!
good luck
mud

 

[kirkland]

me thinks it was a grenade with the pin pulled.
the time you ran it would not be enough to cause your failure
this motor was probaly on its way out before hand
running with the coolant line off didnt help
this would have cooked the motor, maybe turned the nice silver colour gold?
also this loose line could have put enough water in the hull that the engine sucked a bit in, you cant compress a liquid !!!
add in the fact that the carbs were crudded up,before this happened, this will make the boat run lean, lean condtion makes em run really good on the top end, but makes em run really hot, not good!!!
skis live a hard life, rode hard ,put away wet, sit most of the time, sigh!
as karl stated, a rebuilt motor is the best bet
hate for you to put all that money into the top end, for the bottom end to fail and trash all them new parts!
good luck
mud

Hey thanks it didn't have water in it when ran it several times before because I had it apart and got it all out but a little water came from somewhere the last time, thanks for the info.

 

[jhjesse]

Kirkland,
Sent you a PM.

 

[kirkland]

Kirkland,
Sent you a PM.

Thanks for the info, I don't know what happened or if their was a weak point from the overheat before. It was getting oil on the trailer because I checked the plugs I bet 10 or 15 times with different plugs several and just cleaning them off and looking at them several times, they had oil 4 sure and, normal white smoke showing oil also. I have to find out for sure before I do anything, Thanks

 

[kirkland]

Turns out the rod bearing is toast with the piston

Still don't know just what did it, maybe something i did with the carbs, but 2 min is fast to blow I'm sure it had to have damage from before when it got overheated that's ok with premix and a new engine I hope it goes better.

 

[greyrider]

this is my biggest fear - my ski runs great - 56 on dreamometer - grey lines - every connection i have pulled apart shows no green stuff or anydeterioration. but i know i should redo the lines and clean the carbs - with my luck, and apparently yours too, do the right thing and then blammo

still leaning toward doing it all - but getting at the carbs on a lrv are almost impossible - but possible

good luck dude

 

[D 5UPE]

The way the piston was looking clean before it blew could be due to water entering the cylinder under preasure.
That would cause a hydrolic lock and smash the piston.
I have seen pistons blow a hole straight through them because of water entering the cylinder. Your previous over heating may have warped the cylinder head. So have the head checked out and or skimmed. Before reinstalling it.
And use a new cylinder head gasket. Check all gaskets on your exhaust system allso.
You sound like you know quite abit about motors, and its probably you cut a costly corner somewhere. As I do now and then to great expense. :redface:

Good luck and happy skiing.

 

[kirkland]

That's it!!!

The way the piston was looking clean before it blew could be due to water entering the cylinder under preasure.
That would cause a hydrolic lock and smash the piston.
I have seen pistons blow a hole straight through them because of water entering the cylinder. Your previous over heating may have warped the cylinder head. So have the head checked out and or skimmed. Before reinstalling it.
And use a new cylinder head gasket. Check all gaskets on your exhaust system allso.
You sound like you know quite abit about motors, and its probably you cut a costly corner somewhere. As I do now and then to great expense. :redface:

Good luck and happy skiing.

You got it I bet, I saw some water in the front cylinder when I took it apart and the plug instead of being gaped was pushed, bent down touching the other part of the plug I couldn't figure out how that got bent when the piston couldn't have touched it and the back one was the one that burnt up not the front but I did see some drops of water in the front, wow I bet it was a warped head, I looked at it and it looked good but it's hard to see with the naked eye I'm sure, I have rebuilt several car engines and learning about seadoos now only rented them a few times and this engine has been a experiment and learning tool really, so my lesson cost over $1000 it was worth it I just want to learn more and know all I can, and I don't want to make a habbit out of blowing and changing engines, lol. Thanks :agree:

 

[seadoosnipe]

Head gaskets..?

I kinda skimmed through this but see you used the head gasket again, before all this happened. Like Mud said, all that damage could not have happened that fast, something was on it's way out.

I'm only jumping in on the head gasket. You really should not use the head gasket on the 951 but once. On these gaskets, they are just like the ones on your car motors you were talking about. Once they have been torqued, they have been pressed to their designed fit and sealed. When you break that torque, the gasket does not rebound unlike those on the 787's and below. They use the rubber "0" ring type of gaskets. You can re-use them again........but, replace your metal ones.

 

[kirkland]

Live and learn

When the head gasket blew the first time you could tell it blew but this time it looked fine that's why it was so weird but it blew out last time as in exhaust pushing the water out and I wasn't even going but 35 or 40 with clogged carbs and bad diaphragms in the carbs and didn't know it but anyway last time you saw smut and oil in the water passageways this time going even faster (60) it blew water in the chamber going 60 rather than blowing the water out again, it's weird but anything can happen, if you look at all the people that go premix it's crazy, one guy said "rotary valve, what do you mean burn it up with no oil tank mine and it's been that way since 98" he said he put some tubes together and put synthetic gear oil in it and he can put it in there when he needs to, some said they burnt one up and changed a fleet of skis to premix, no problems since, one place said the recommend it for their engine rebuilds but it wont void the warranty if you use a working pump, they seem to be happy with it but just getting a bunch of views because I have no clue, lol. Thanks for the tip :cheers:

 

[kustomkarl]

Your 2000 gtx has Reed valves and not a rotary valve system...so no oil tubes on your model to worry about. As far as oil injection, the forum will have lots of opinions. I have not seen oil pumps go bad...but lots just want confidants it isn't a problem.

 

[seadoosnipe]

Expansion and contraction...

When the head gasket blew the first time you could tell it blew but this time it looked fine that's why it was so weird but it blew out last time as in exhaust pushing the water out and I wasn't even going but 35 or 40 with clogged carbs and bad diaphragms in the carbs and didn't know it but anyway last time you saw smut and oil in the water passageways this time going even faster (60) it blew water in the chamber going 60 rather than blowing the water out again, it's weird but anything can happen, if you look at all the people that go premix it's crazy, one guy said "rotary valve, what do you mean burn it up with no oil tank mine and it's been that way since 98" he said he put some tubes together and put synthetic gear oil in it and he can put it in there when he needs to, some said they burnt one up and changed a fleet of skis to premix, no problems since, one place said the recommend it for their engine rebuilds but it wont void the warranty if you use a working pump, they seem to be happy with it but just getting a bunch of views because I have no clue, lol. Thanks for the tip :cheers:

I have read where quite a few do this. I do not recommend it because what they do is pretty much, seal that system off. It needs to breath, that's why it has a vent line on it. When the crankshaft and worm gear start heating that oil, it puts off a vapor. They need to allow that heat to vent. Sealed, where they take a tube over and connect to the other side will eventually, cause the seals on the crank to start leaking.

Premix?.......I'd opt for a good working oil pump anyday. I was working on a GTS that was being premixed. Just in the week or so I had it, I could tell that the premix would be a very expensive way of lubing my motor. When you premix, your wasting over half the oil............:ack:

But, like Karl said, the 951 does not use the rotary valve system. So, you don't have much to worry about. If you ever worry about your oil pump, you can test it for flow to make sure it's working properly.

There is another test you can do while on the engine too. With it running at idle on the hose, reach down and wind the cam on the oil pump wide open. Give it about a minute and it should start smoking like a mosquito truck. If so, then you know your oil delivery is sufficient.:cheers:

 

[kirkland]

Thanks

Thanks for all the info on all the subjects, I may have blamed the oil pump when it was water, don't know but everything will be checked when the new engine in put in, that engine is easy to work on I think, I had it down to pistons hanging out and nothing but a block yesterday in 45 min to see how bad it was. Today I took the rest of it out in about 20 min, lol. Putting it back takes a little more time, anyway thanks.:cheers:

 

[D 5UPE]

You cant beat practice to get faster on engine jobs. :rofl:

I think I have to thank airfix for my mechanical skills.:lols: