Yz250 piston symptoms

Blackjack31
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Blackjack31
Curious why my piston has indentions from the wristpin bearing sleeve thing. I can’t think of the name right now. But the silver rod that goes through the wrist pin looks to be getting stuck and causing wear. Also, the carbon build up on the bottom of the piston. I’ve read it’s from running to lean. Which is understandable cause I dropped one main jet size due to smoking.

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Paul_Pitzonka
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Paul_Pitzonka 9/21/2019 4:02pm
9/21/2019 4:02pm Edited Date/Time 9/21/2019 4:06pm
That’s not from running lean that’s from transmission oil entering the crank case... more than likely a bad crank seal, or the case is no longer sealing between the crankcase and transmission... I’m a little lost at your wrist pin question... if you’re referring to the machined recess in the journal that’s to aid in lubrication of the wrist pin...
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Blackjack31
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Blackjack31 9/21/2019 4:24pm
9/21/2019 4:24pm
Paul_Pitzonka wrote:
That’s not from running lean that’s from transmission oil entering the crank case... more than likely a bad crank seal, or the case is no longer...
That’s not from running lean that’s from transmission oil entering the crank case... more than likely a bad crank seal, or the case is no longer sealing between the crankcase and transmission... I’m a little lost at your wrist pin question... if you’re referring to the machined recess in the journal that’s to aid in lubrication of the wrist pin...
Yeah I replaced the crank seal wet side and dropped the main jet 1. It didn’t do anything about the smoking and so I put another one in. I may have installed it wrong. I tore it apart and took it to a shop and they took it out and put the new one in. It’s good now. There’s about 25 hours on it now so I’ll put a new piston in shortly. At least change the rings. See if there is any under this piston. So that mark is made to be there? I just put a cr125 piston in and was looking at pistons around the shop and I seen that one and the Honda’s was not made that way. So I’m guessing it’s made that way on the yz250? I’ve never really inspected a new piston, I just check the clearance and drop it in haha.
Paul_Pitzonka
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Paul_Pitzonka 9/21/2019 4:31pm
9/21/2019 4:31pm
Paul_Pitzonka wrote:
That’s not from running lean that’s from transmission oil entering the crank case... more than likely a bad crank seal, or the case is no longer...
That’s not from running lean that’s from transmission oil entering the crank case... more than likely a bad crank seal, or the case is no longer sealing between the crankcase and transmission... I’m a little lost at your wrist pin question... if you’re referring to the machined recess in the journal that’s to aid in lubrication of the wrist pin...
Blackjack31 wrote:
Yeah I replaced the crank seal wet side and dropped the main jet 1. It didn’t do anything about the smoking and so I put another...
Yeah I replaced the crank seal wet side and dropped the main jet 1. It didn’t do anything about the smoking and so I put another one in. I may have installed it wrong. I tore it apart and took it to a shop and they took it out and put the new one in. It’s good now. There’s about 25 hours on it now so I’ll put a new piston in shortly. At least change the rings. See if there is any under this piston. So that mark is made to be there? I just put a cr125 piston in and was looking at pistons around the shop and I seen that one and the Honda’s was not made that way. So I’m guessing it’s made that way on the yz250? I’ve never really inspected a new piston, I just check the clearance and drop it in haha.
It’s called a broach technically, and it’s a better oiling design than your standard blank wrist pin bore... some oem pistons have them some don’t...
Blackjack31
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Blackjack31 9/21/2019 5:52pm
9/21/2019 5:52pm
Paul_Pitzonka wrote:
It’s called a broach technically, and it’s a better oiling design than your standard blank wrist pin bore... some oem pistons have them some don’t...
Oh cool. Learn something new every time I get on here. Thanks man

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