Blaster Help help help help

[markg423]

im havimg major problems with my 701....it keeps blowing up the front cylinder ive tried everthing
im running 62t 82 mm dual 38s ada head 180 psi comp riva pipe duel cooling from the pump
its blown up 4 times in a row ive changed everything jettin is good piston clearance is right ring end gap is right
im at a loss no more ideas
any info would be great thanks:aargh4:

 

[yamanube]

Leak down test?

 

[NISMOtuner]

Are you sure you have your carbs set right? Running lean destroys the engine. I'm assuming your running 93 octane? And can you show pictures of what it does to the front cylinder? If your running dual carb then my first guess would be that your front pistons carb is running lean and causing knock which is destroying the cylinder. A lean running engine can run like a scalded dog until it blows up.

 

[markg423]

the carbs are clean an fresh the jetting i got from blowsion not sure if its a good set up
135 hs 70 ls 1.5ns 95g hs 1 1/2 out ls 1 1/4 out just keeps melting the front cylinder the rear one looks perfect
at 180 psi should i be alot fatter? an also the cylinders are resleeved an the exhaust ports are pretty high

 

[jcagle]

does anybody know how to message someone on this website

 

[markg423]

 

[FearMyWrX]

does anybody know how to message someone on this website

You need 5 posts before you can PM.

 

[227]

Back in my 550 days I had a buds whos ski was doing the exact same thing. Turns out it was an out of circle bore in the cylinder. On throttle, hot spots would occur and it would stick a piston. Your piston damage looks different than his but I would definately get your cylinder checked at a machine shop

 

[markg423]

yea the cylinder was just sleeved an bored

 

[OCD Solutions]

What size domes are you running? We had a motor a couple years back doing something similar. We thought it was a porting issue but it was related to compression and ring gap. I tried to find the thread but it's too old I think.

If we ran the larger domes then it would run for hours just fine, swap in the tighter domes and it would eat a piston and break off the corner within 45 mins. The only difference was that we had the same issue in both cylinders.

I believe it all came down to ring end gap and the solution was to open it up to .018 to .020. Higher compression was causing more heat and the ring was expanding enough to catch the exhaust port.

Your resting compression may record a bit lower but it will tighten up once up to operating temperature.

 

[markg423]

im running 35 cc domes the piston clearence is good an the ring gap i set to the pistons spec.....im leaning torwards jetin....how much do you think the comp would go up when it gets hot

 

[OCD Solutions]

Found it...read thru this thread.

http://www.x-h2o.com/threads/57246-High-compression-domes-snagged-rings

EDIT: I just called my buddy to refresh my memory of the situation and he said he increased the ring gap and that it still ate a couple pistons after that. He finally gave up and just ran the 38cc domes with lower compression.

Since you just had them resleeved and bored, I would go back to the machine shop as suggested above and have them measure everything again. Have them check the bore, check the chamfer on the ports, make sure port heights are identical and that the sleeves are matched. something has to be off with that front cylinder.