Piston and Cylinder crapped out - Yamaha Raptor Forum
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post #1 of 24 (permalink) Old 06-13-2019, 05:39 AM Thread Starter
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Piston and Cylinder crapped out

What can cause this kind of damage to the piston and cylinder? This was a brand new CP Carillo piston and OEM cylinder on a recently ported and polished head. Connecting rod was also new cp carillo, and new cams stage 2.
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post #2 of 24 (permalink) Old 06-13-2019, 06:43 AM
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Originally Posted by palvarez05 View Post
What can cause this kind of damage to the piston and cylinder? This was a brand new CP Carillo piston and OEM cylinder on a recently ported and polished head. Connecting rod was also new cp carillo, and new cams stage 2.
Holy cow! That sucks. Cylinder looks like it may have gotten a little hot, may just be from the scoring. Not an expert at all, but I believe those cp pistons especially have to have their rings file fit to your cylinder, do you known If this was done? They are typically big to start with so you can properly gap them to the application, if this was not done then expansion make have caused them to bind up.
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post #3 of 24 (permalink) Old 06-13-2019, 07:01 AM Thread Starter
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Holy cow! That sucks. Cylinder looks like it may have gotten a little hot, may just be from the scoring. Not an expert at all, but I believe those cp pistons especially have to have their rings file fit to your cylinder, do you known If this was done? They are typically big to start with so you can properly gap them to the application, if this was not done then expansion make have caused them to bind up.
I will ask, looks like the piston literally melted... It is so weird...

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post #4 of 24 (permalink) Old 06-13-2019, 07:31 AM
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The piston was wrong size for the bore. Way too tight. Fine at room temps but once it heated it was tight so there is the results.

I build two stroke racing engines and if you don't take some off the top 1/2" of piston especially the little bit above the ring that needs .002" taken off(.004" total off diameter) the same thing will occur.

Rings with not enough end gap will cause similar damage. Were the rings checked/gapped during installation
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post #5 of 24 (permalink) Old 06-13-2019, 07:48 AM Thread Starter
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The piston was wrong size for the bore. Way too tight. Fine at room temps but once it heated it was tight so there is the results.

I build two stroke racing engines and if you don't take some off the top 1/2" of piston especially the little bit above the ring that needs .002" taken off(.004" total off diameter) the same thing will occur.

Rings with not enough end gap will cause similar damage. Were the rings checked/gapped during installation
So no matter what piston I purchased, some needs to come off?

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post #6 of 24 (permalink) Old 06-13-2019, 08:09 AM
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Looks like detonation damage to me. From low octane, old gas, to much compression. CP pistons don't need any extra machining but the ring gap must be checked. What's your elevation and compression of the piston?
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2007 RAPTOR 700, SAND QUAD, 11:1 CP, +5 HR CRANK, PC3, +2 TB, LONE STAR XC +1, +1 A-ARMS, HD TIE RODS, JOGACA REAR SHOCK, ASV LEVERS, +4 REAR AXLE, DR.D REVERSE, ODI GRIPS, 1 1/8 CARBON BARS, DG BUMPER. BILLET: GAS CAP, BRAKE COVER, THROTTLE LEVER, BAR MOUNTS. LED LIGHTS'
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post #7 of 24 (permalink) Old 06-13-2019, 08:34 AM Thread Starter
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Looks like detonation damage to me. From low octane, old gas, to much compression. CP pistons don't need any extra machining but the ring gap must be checked. What's your elevation and compression of the piston?
So this was what i though... Pump gas down where i ride my bike is pure shit and excuse my french, it doesnt have an octane rating. The piston was 12:1, altitude is around... 26'
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post #8 of 24 (permalink) Old 06-13-2019, 09:29 AM
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Originally Posted by DEZPERADO View Post
Looks like detonation damage to me. From low octane, old gas, to much compression. CP pistons don't need any extra machining but the ring gap must be checked. What's your elevation and compression of the piston?
So this was what i though... Pump gas down where i ride my bike is pure shit and excuse my french, it doesnt have an octane rating. The piston was 12:1, altitude is around... 26'
12 to 1 usually requires about 100 octane I believe.
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post #9 of 24 (permalink) Old 06-13-2019, 12:07 PM
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Did this happen on the first engine run after the build? Did you gap the rings? The intake valves appear to be bent.
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post #10 of 24 (permalink) Old 06-13-2019, 01:02 PM
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No octane rating on the gas pumps?? Do you have regular and premium? You need to ask or do some research.

At basically sea level, I would rebuild with a CP 11:1 and run the best gas you can. If you find your gas is less then 90 octane I would machine around .030 from the piston dome. You may see a slight power loss but without detonation. Get a Stage 3 cam and a +3 throttle body will give more power.

Run a (diamond) hone thru the cylinder to see if it will clean up.

I also saw what looked like bent valves, be sure to check them.

Be sure to check the head for warpage and always use a factory head gasket.

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