Keeps blowing pistons

Paul_Pitzonka
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Paul_Pitzonka 8/12/2019 10:02am
8/12/2019 10:02am
Paw Paw 271 wrote:
That shows to be a "cold sieze". This can happen when the engine is not allowed to fully warm up prior to putting it under a...
That shows to be a "cold sieze". This can happen when the engine is not allowed to fully warm up prior to putting it under a hard load. ( You know how most kids are...Crank it up and then take off full blast all in about 10 seconds.)

How many heat cycles did you put the engine through prior to allowing the kid to get wide open?

I would not rull out a leaking head gasket as well.

Paw Paw
I’m on board with this... either a cold seizure from running cold engine under load or you have something (I believe coolant) washing the bore clean... 3 pistons with the same outcome, even after a replated cylinder, I highly doubt it’s a piston to wall clearance issue, and after seeing the piston that’s not an air leak seizure...
SBD
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SBD 8/12/2019 10:34am
8/12/2019 10:34am
How often were you replacing top end ? At how many hrs ?
Ryan_Paez
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Ryan_Paez 8/12/2019 10:44am
8/12/2019 10:44am
Y would it be washing bore clean what is doing that an I just bought the bike in June an it was a complete rip down an rebuild they even went as far as putting ceramic bearing in. But when I got it they had bike set up for hill climbs so they had it lean an never said nothing so that how 1st one blew then got it fixed just had bore Honed an put new one in an it blew but I think that one blew cause Nikolsil was gone an then 3 rd one it ran for about 10 hrs an Sunday we went riding rode for about a hr an then on way home it blew but I smell a anti freeze smell coming from it no leaks of coolant anywhere
SBD
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SBD 8/12/2019 10:54am
8/12/2019 10:54am
If the head gasket is leaking into the cylinder it will wash the oil away that is in the gas.
That is the only lube the top end gets. That would explain the smell, and the fact that you dont see any coolant leaking.

Make sure your jetting is stock also.

The Shop

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Ryan_Paez
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Ryan_Paez 8/12/2019 11:04am
8/12/2019 11:04am
The gasket was a little funny looking was kinda bent at 1 side of it. Do u think it could of messed up the head where spark plug goes
Matt Fisher 8/12/2019 12:04pm
8/12/2019 12:04pm
Have the top of the cylinder checked for flatness too. Replacing a warped head onto a bad cylinder would result in the same problem.

To make sure it fully warms up, idle the bike until the cylinder is warm to the touch, then ride it for a couple minutes at a very gentle pace, like a first time rider would do. When at the track, I use this time to idle around the edge of track for one lap, making sure it hasn't been changed since the last time I was at that track.
mxracer515
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mxracer515 8/12/2019 1:03pm
8/12/2019 1:03pm
Is that a " B " on the piston? Do you have an A cylinder? Or re-plated with tighter tolerances?

Did you clean the piston off, I see NO residual pre mix?

Was gas added that had no oil in it? Ask around your area for a moto centered shop to do the repairs.

The avg. shop may just be parts changers & not actual mechanics / techs. Who will try & find the root problem.

Ryan_Paez
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Ryan_Paez 8/12/2019 1:36pm
8/12/2019 1:36pm
Yea that was 1 st one that blew it was way to lean
Ryan_Paez
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Ryan_Paez 8/12/2019 1:37pm
8/12/2019 1:37pm
Ryan_Paez
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Ryan_Paez 8/12/2019 1:39pm
8/12/2019 1:39pm


mkinney
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mkinney 7/3/2020 2:40am
7/3/2020 2:40am
Did you find the issue? Also have same issue kx 85 ‘15
soggy
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soggy 7/3/2020 7:01am
7/3/2020 7:01am
Find a reputable builder to take the engine too rather then just throwing money at it in parts without knowing why it's blowing up.
2
JMCR250
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JMCR250 7/3/2020 9:22am
7/3/2020 9:22am
Pretty sure you have coolant leaking into the bore, as others have said. Causes could include warped head/cylinder deck and/or bad head gasket. This is doing two things: 1) coolant is washing oil off the piston, and 2) the bike is overheating, especially under a load. Depending on where the coolant leak is, you may also be sending hot cylinder gasses into the coolant lines, which pressurizes and overheats the coolant. I'd have a professional mechanic look over the top end and cooling system.
skankhunt69
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skankhunt69 7/5/2020 8:52am
7/5/2020 8:52am
Check jetting, run iridium spark plugs I’ve had the regular Ngk ones break. Use Oem piston. Try running motul 800 for premix.
Ryan_Paez
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Ryan_Paez 7/5/2020 5:30pm
7/5/2020 5:30pm
mkinney wrote:
Did you find the issue? Also have same issue kx 85 ‘15
No I never did I gave up on it for a while I’m just gonna but a new engine an try that out I think

Pit Row

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