Not sure why this is happening. This is the second time piston went. (Rear this time) Last week was the front!? First tank of gas after rebuild. New pistons, rings, everything. It was broken in properly. Ski felt fine until we checked compression, 40 rear. Pulled head and this is what it looked like. Can anyone chime in and help me figure this out??
Need help blown piston
- Thread starter sxrchris
- Start date
- Location
- the jetski grave yard
what do you mean, ski felt fine until comp check? it was blown the F up before you checked comp. NOT ENOUGH INFO! did you look at the crank at any time? tear it all apart and check everything.
^^^ Agreed...... My 701 did that too years ago, shard a piston.
In my case I had 190 compression, MSD enhancer, do not know if stator was advanced too, type 4 dry pipe, I ran California 87 octane fuel in it and found while at wide open throttle racing another craft it shared the piston. The broken peices got between the crankshaft counter weight and broke/cracked the lower case. Destroyed the head dome too. Had to tear all the way down and rebuild, clean the metal out. After completed I set the stator at zero degrees and ran 100 % race gas 110. Later I realized this was overkill for my set up and riding style and ran 50/50 91 and 110. No more issues in my case but I did modify my riding style after wards, little less wide open. The buzzards right not enough info on your specific case.
In my case I had 190 compression, MSD enhancer, do not know if stator was advanced too, type 4 dry pipe, I ran California 87 octane fuel in it and found while at wide open throttle racing another craft it shared the piston. The broken peices got between the crankshaft counter weight and broke/cracked the lower case. Destroyed the head dome too. Had to tear all the way down and rebuild, clean the metal out. After completed I set the stator at zero degrees and ran 100 % race gas 110. Later I realized this was overkill for my set up and riding style and ran 50/50 91 and 110. No more issues in my case but I did modify my riding style after wards, little less wide open. The buzzards right not enough info on your specific case.
Magyar68
Really!!!
- Location
- Lewisville
During your Break-in did you check your plugs every hour of operation? Looks like that Piston was starving for gas.
What does the dome look like, and post a pick of that plug.
What does the dome look like, and post a pick of that plug.
Quinc
Buy a Superjet
- Location
- California
Someone at the lake this year told me he blew his front piston because he sheared the flywheel key. So maybe check your flywheel, and stator/timing.
Magyar68
Really!!!
- Location
- Lewisville
that would explain both Failures...
Blue
Judging your cheapness
- Location
- St Cloud Florida
That my friend is detination you can look at the picture of the front piston and you can clearly see that the wash pattern is a lot better. the back cylinder is lean possibly due to a carb issue?? Need more info.....
Sent from my SAMSUNG-SM-N900A using Tapatalk
Sent from my SAMSUNG-SM-N900A using Tapatalk
Stock timing, 180-180
Plugs looked wet. Both cylinders looked like they were oiled up pretty well.
It's my buddies ski, I'll work on getting pics. The rear dome was gnarly
- Location
- the jetski grave yard
octane has nothing to do with it. if you only knew. i run piss yellow turpintine smelling 3 year old gas with bugs floating around in it, in some of my motors that have 205 or 210 comp and full race porting. i dont just pin it for 1/4 mile runs but i dont not WFO it either and they never blow up or show signs of detonation. i dont waste old gas and my local shop actually saves me all the old gas from skis he services. free gas for the weekend : )=
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It's a Yamaha Blaster 2, stock exhaust. Same thing happened in front cylinder the first time he was riding. It lost power after running wot. He was running 87 octane.
That's exactly what happened to me on 87 octane during extended wide open runs. If you continue to run wide open on that low octane fuel the same thing will happen again guaranteed!!! That engine is a 64x cylinder? With high port timing? 150 cranking psi on that cylinder is equivalent to 180 on a 61x cylinder? Boats heavy too. You need more octane fuel and if your going to ride that way you need even more octane. Worked for me.
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760 62t cylinder 180 psi recommended 98 octane by ADA Racing with an ADA head and squish. Yours is a 64X.
Did both events happen at wide open?
You should look for things that effect both cylinders equally and at wide open in addition to the low octane to be safe. Causes of lean fuel @ high speed should be considered and checked as well.
I guess Group K had problems wiping out pistons too due to heat on one of there test kits, the only way they got that kit to stop wiping out pistons was 105 octane.
http://www.groupk.com/y753b2.htm
Two timing curves, one for each cylinder, stagared compression stock front and rear for more even heat. Differant port heights, Unique boat
Did both events happen at wide open?
You should look for things that effect both cylinders equally and at wide open in addition to the low octane to be safe. Causes of lean fuel @ high speed should be considered and checked as well.
I guess Group K had problems wiping out pistons too due to heat on one of there test kits, the only way they got that kit to stop wiping out pistons was 105 octane.
http://www.groupk.com/y753b2.htm
Two timing curves, one for each cylinder, stagared compression stock front and rear for more even heat. Differant port heights, Unique boat
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Ive run old gas in the past, 2 year old or so left over, mixed maybe almost one gallon into each 5 gallon container with 4 freash gallons, went ok but i dont keep it around now, use what i buy in a resonable time frame. Free gas is hard to turn down though
Little story worth mentioning maybe. Late model Van comes in for a drivability concern, PO304 misfire DTC, runs like poop, backfiring in the intake, resembles a broken valve spring, this paticular engine does that once in a blue moon, its still under factory warranty so the valve covers are removed for a visual inspection. Find #4 cylinder valve spring is ok but the pushrod is bent and out of place?, install a new pushrod and rocker shaft assembly and restart it, same issue again, puill the valve covers back off and the push rods bent again and has broken the foot of the rocker WTF. Tear the cylinder heads off, fuel that spills out the fuel rail stinks. Inspect cam and roller lifters both look good but the engine cylinder walls have this funny dry parched look. Inspect the cylinder #4 valves find the intake or exhaust i forget which is closed and will not come out of the valve guide, its malled in there. Took a fuel sample to send out for tesing, smalls real bad, stinky, the factory is involved now. Pull the pistons and the rings are all stuck in the groves, cylinders dry and parched and scuffed. Everything the fuel touched that was internally lubricated or not was damaged. The porter who dropped the customer off said they lived on a large ranch, later We found out they were fueling out of their own tank. Long story short, this was not a warrantable repair, coverage was declined. The engine, fuel rail, fuel injectors, fuel pump and fuel tank all had to be replaced costing the customer $8000 to 10,000 dollars. I think they got their car insurance involved after manufacturer declined repair. Old fuel may work but when it doesnt its flipping expensive, not sure its worth messing with for the average Joe
Philip Clemmons
Owner, P&P Performance
- Location
- Richmond, Va
Verified stock timing, or "I set it stock" timing ?