mag cylinder looks like a bomb went off

[demos10]

ok. its a 1998 gs with the single carb 717 motor. mag cylinder is a brownish black and the cylinder head has what looks like a sticky varnish. Pto cylinder looks great. I am thinking that I lost the oil injection to the front cylinder? Also it ate the spark plug and dented the piston. What do you guys think? top end and premix from now on?

 

[doc12]

When fixing a motor, it is important to always find out the cause of the problem. Sounds like you need to pull the motor.

 

[brock1]

pictures would be great..... as far as fixing it i agree with DOC12 you need to pull the engine and inspect it and find the problem...By the way if the top of the piston is dented and the spark plug is messed up thats a sign that the rod let go and allowed the piston to shoot up towards the plug....

 

[KyleB]

pictures would be great..... as far as fixing it i agree with DOC12 you need to pull the engine and inspect it and find the problem...By the way if the top of the piston is dented and the spark plug is messed up thats a sign that the rod let go and allowed the piston to shoot up towards the plug....

:agree: Anytime you have damage like that something turned loose. You need to find out what it was and fix it. Pulling the engine apart is the only way. :cheers:

 

[demos10]

ok here are pics

 

[brock1]

will the engine roll over at all??? if so does that piston move up and down....my gut says it doesent.... my guess is your rod let go of the piston..your head also looks like its pitted...is this the 720 or the 657 engine

EDIT....its a 717 just reread your post...... if u need parts i have SOME

 

[demos10]

turns over fine. not pitted, its metal from the spark plug. see how black the head is? its not oily its alittle sticky.

 

[brock1]

so just to confirm when you roll it over THAT piston still moves up and down fine???

 

[demos10]

correct moves up and down no problem. the rear cylinder head you can see is shiny and has a slight oily film. think i just lost oil to front cylinder since i only have the one carb. thing ran awesome for 3 or 4 minutes then just stopped and I had to paddle to shore

 

[brock1]

looking more closely at your pictures i would say that it got REALLY REALLY hot and melted the plug and made a crater in the piston...that has nothing to do with oil...if you lost oil injection the cylinder walls would be gouged and the piston would be melted to the cylinder walls...what plug are u running in that cylinder ???

 

[Rotor13B]

ok here are picsView attachment 13800View attachment 13801View attachment 13802View attachment 13803

That looks like detonation to me. Possibly a timing issue.

 

[demos10]

it had ngk br7es. got it used and that was in it

 

[KyleB]

I initially thought something turned loose and caused your problem but after looking at your pics I tend to agree with Rotor. Looks like detonation. There is a really good thread on the forum that discusses this and shows pictures. I think Seadoo Snipe started it. Try searching and see what you come up with. If I remember correctly I think there is a picture that looks almost exactly like this piston and the cause is discussed. :cheers:

 

[donkey]

maybe a crank end seal went bad,causing a lean condition.?

 

[demos10]

maybe a crank end seal went bad,causing a lean condition.?

that is what i am starting to think now since it is a single carb and the rear cylinder is normal.that and maybe the intake gasket on that side?

 

[demos10]

also somebody correct me if i am wrong but impoper timing would have affected both cylinders not just the front one right?

 

[Rotor13B]

also somebody correct me if i am wrong but impoper timing would have affected both cylinders not just the front one right?

Anything is possible but you're probably right. Unless I'm looking at it wrong it looks like that motor has been rebuilt before. I'm wondering if this is what caused the rebuild.

 

[donkey]

maybe the crank is twisted a bit,that could advance the rear piston in relation to the pto piston,or the other way around,?um,nope that would not change spark timing ,just piston timing.hmm

 

[Rotor13B]

maybe the crank is twisted a bit,that could advance the rear piston in relation to the pto piston,or the other way around,?um,nope that would not change spark timing ,just piston timing.hmm

Doesn't matter, If one is out of sync you would get the same result.

 

[demos10]

Thanks to everyone for the input. Gonna pull the motor and take a look see. Guess I got to spend some money on a pressure tester

 

[brock1]

if its been rebuilt once already and you have that kind of damage right now i would suggest getting a new engine or at least a good used one from 99spxxx or minnetonka...you can only bore so far and with a crank as old as yours you will be doing another rebuild in the future if you dont replace the crank also