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Welp I was riding on a straight away... Lol in 5th gear I didn't have it pinned I was just playing with the throttle then blup blup blup she goes when I tried to kick it over it was very tight as in something blew up just took the head off and this what I see the bike has 27.5 hours on pro X piston from Amazon. what can it be

 

IMG_1862.JPGIMG_1861.JPGIMG_1860.JPGIMG_1859.JPG

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i had literally just ridden it like 5 min before i got back on it & i think it's the bottom i just tried to rotate it it's kinda locking up & i run 32:1 & jd jetting did my jetting this was back in march tho it's hotter now like 97 but i was riding it when the sun was down

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Cold seizure? Did you warm it up before you took off? 
Looks pretty hot also, what is your mix, jetting, routine?

Image1500493282.895619.jpgImage1500493325.812434.jpg the plastic look melted

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The metal is discolored man, it must've overheated or lack of lubrication.

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I'd check your cooling system, does it have enough coolant and stuff. Also how does your water pump look?

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I ran 32:1 always measured it. My coolant was good when I had left . I took a 30 min. I found a then copper shaving on top of the bottom end

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Those plastic stuffers are melted. I guarantee your big end crank bearing is toast. Time to pull it down and rebuild the crank. 

It's a 1999 yz250 do you have a link to a kit? And what I will need
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If you wanna rebuild your crank, I'd recommend someone like Ken O'Connor racing. They've got good reviews. I know a few guys who sent their worn cranks out. He does a good job for a reasonable price.

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2 hours ago, Ayeecole said:


It's a 1999 yz250 do you have a link to a kit? And what I will need

I have mine rebuilt with a ProX rod and bearings.  They are the same as OEM and not cheap Tiwanese bearings that will fail prematurely. 

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6 hours ago, ASP1227 said:

If you wanna rebuild your crank, I'd recommend someone like Ken O'Connor racing. They've got good reviews. I know a few guys who sent their worn cranks out. He does a good job for a reasonable price.

Yup, KOR does good rebuilds.

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