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Kids CR125R went tight last week, finally got around to taking top end off, back side of piston skirt broke off. Anyone know what would cause this? Also do I have to split the cases to clean? Piston came apart right by the oval on the intake side. I also got a pretty good sized chunck out that had it locked up.Zero up and down slop on the crank so I think thats ok. Any help would be appreciated...

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you dont need to take the bottom end apart. just flush the bottom end out with diesle to get everything out and blow it out with air good.

as for what made the piston crack, it happens with cast pistons on high HR bikes. i personly havenver had it happen, but hear about it alot.

up and down ply isnt the only thing you want to cheak for in the crank, messure the side to side play as well and make sure it is in spec. wrk out thrust bearings/washers are just as bad as a worn out big end bearing.

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OK explain to me how you would flush it out. THANX..... First time bike owner and this is all new to me... Im used to workn on sleds.

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OK explain to me how you would flush it out. THANX..... First time bike owner and this is all new to me... Im used to workn on sleds.

DUH...... Nevermind.... Drain plug on the bottom.... Not to hard to figure out.:ride::bonk:👍

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DUH...... Nevermind.... Drain plug on the bottom.... Not to hard to figure out.:ride::bonk:👍

same as a sled man.

pour the fuel into the crankcase, swish it around well, turn the motor upside down, let everything run out, and blow it out with air.

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That drain plug will only drain the gearbox which is separate from the area you want to flush. Like capt justin said, "Flip the bike over"

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Ok wouldnt it be easier to just take the motor out of the frame????????????

Your call. I think it was assumed you'd rather not pull the motor out. I would though.

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you dont need to take the bottom end apart. just flush the bottom end out with diesle to get everything out and blow it out with air good.

Is diesel a better solvent than gasoline? Would gasoline work similiarly or poorly?

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allright. im gonna say it.

the skirt broke because of excessive piston to cylinder clearance. the only way that happens is with HIGH hours on a bike.

Since this happened i believe it is safe to assume that the bike is ready for the crank and bottom end to be rebuilt.

I personally have done the diesel rinse before, i got another topend out of my bike before the crank seized.

personally i would not do that again. for another 200 ish bucks you can have a completely refreshed motor.

I would also suggest Mic'ing your bore to make sure its not too far out of spec.

good luck and have fun

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Is diesel a better solvent than gasoline? Would gasoline work similiarly or poorly?

in my opinion it is. it is not as flamible as gas, dosent stink as bad as gas and dose not fume as bas as gas.

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in my opinion it is. it is not as flamible as gas, dosent stink as bad as gas and dose not fume as bas as gas.

Sold. 👍

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i used kerosene (had it on hand) and then put a little 2t oil on the crank/bearing sufaces and journals before rebuild.

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Diesel and kerosene are essentially the same thing.

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