What caused this

9/16/2017 6:40pm Edited Date/Time 9/19/2017 3:13am
Kx 144 piston after 4 hrs. The jagged thing u see on the top of the piston is the spark plug tip.

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ferg722
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219
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6/21/2016
Location
Pitt, PA US
9/16/2017 7:57pm
Congrats, looks like you've melted a piston. Is the underside of it black? Did you change your jetting after going from a 125 to 144? What octane fuel and oil ratio you run?
BobPA
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8023
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10/31/2013
Location
PA US
9/16/2017 8:02pm
Detonation I would say. Get a better picture of the top f the piston.
rmoto003
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926
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2/26/2017
Location
Gulf Shores, AL US
9/16/2017 8:02pm
Flux capacitor let go
Hcallz5
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2821
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8/20/2013
Location
UT US
9/16/2017 8:10pm
Could be a number of things. air leak? water pump failure? shit jettting?

The Shop

Knoby
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219
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11/6/2013
Location
Wichita, KS US
9/17/2017 9:22am
Sprocket bolts
Bruce372
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6341
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4/1/2008
Location
US
9/17/2017 10:39am
Big time detonating from poor fuel, jetting, aggressive ignition and head setup.

People moan about the cost of the oem spark plug on the rm125, but it's well worth using it on any 125 imo since it resist the ground strap coming off .

That said, that bike had major problems before the plug let go.
9/17/2017 4:11pm Edited Date/Time 9/17/2017 4:13pm
ferg722 wrote:
Congrats, looks like you've melted a piston. Is the underside of it black? Did you change your jetting after going from a 125 to 144? What...
Congrats, looks like you've melted a piston. Is the underside of it black? Did you change your jetting after going from a 125 to 144? What octane fuel and oil ratio you run?
It's set up for pump fuel and I run 32:1 with 92 octane. The underside isnt black tho
9/17/2017 4:12pm
Knoby wrote:
Sprocket bolts
Thanks. But that was the first thing I checked after it blew up. I already concluded that it wasnt the sprocket bolts.
Paw Paw
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679
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12/24/2011
Location
Benton, LA US
9/17/2017 7:20pm
Bruce372 wrote:
Detonation
X2..... Most likely cause for this is that the head to piston squish was not reset for the larger piston. With out the squish being reset it will cause a lack of lubrication to the edges of the piston and cause sever over heating. The over heating will also cause the plug tip to break off and then stamp the top of the piston. It also causes the pitting on the outer edge of the piston. The piston edges get so hot that it deforms and sticks the piston rings and you loose compression.
The head must be recut to match the oversized piston and create the correct squish clearance. You will also need to be sure to use the correct spark plug for that bike and not a knock off or cross referenced spark plug to be as sure as you can that the plug tip will not break again.
You will also need to do a leak test and a vacuum test to be sure you are not creating a lean condition.
Your jetting will also need to be checked and corrected as it looks to be running lean.
These 144 kits are not just a drop in and go item. They do work great when set up correctly.

Paw Paw
mark911
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360
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3/28/2015
Location
Ashville, OH US
9/18/2017 12:21am
If the head looks similar my guess would be either you sucked some debris in through the intake or your rod bearing is starting to go. Inspect the rod big end very closely, particularly the cage.

Otherwise, probably detonation.
mingham97
Posts
854
Joined
7/16/2013
Location
AU
9/19/2017 3:13am
You can't go wrong with NGK. I think they're standard in Yamahas. They're also like $12.95 AUD here. CR8A for YZ125

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