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dfr136 dfr136
11/23/2020 3:36 PM

Does this wear look normal? 2020 yz125, 30 hrs on cylinder, 14hrs on this piston. Nothing you can feel, just weird looking above the pv and lines on the ports.


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Paw Paw 271 Paw Paw 271
11/24/2020 10:55 AM

I see what looks like to be a ring ridge worn into the cylinder. It that is the case then the cylinder needs work. At any case have it measured before doing anything.

Paw Paw

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dfr136 dfr136
11/24/2020 11:27 AM
Paw Paw 271 wrote:

I see what looks like to ...more

What is a ring ridge and is it normal wear or would something else cause it?

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dfr136 dfr136
11/24/2020 1:43 PM

Couple better pictures

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dfr136 dfr136
11/24/2020 2:52 PM
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rjg rjg
11/24/2020 8:56 PM

Extremely rough method for diagnosis: Take a small chrome wrench and lightly tap with the open end on those polished areas above the pv. Listen for a ringing sound- no ringing sound or you hear a dull sound means you are down to aluminum. Tap around on other parts of the cylinder to get an idea of what the ringing sound is like for comparison. If there is coating left then it will sound like a porcelain ringing.

Otherwise get it measured.

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Mr. Robinson Mr. Robinson
11/25/2020 7:08 AM

Looks like the ring end gap might be a little tight.

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dfr136 dfr136
11/25/2020 7:29 AM

This was a B cyl with a B piston. I’m gonna have it looked at this weekend. Could I check ring gap with the old ring or could I check it with a new ring.

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dfr136 dfr136
11/25/2020 10:03 AM

I measured ring gap with a new ring and I'm right in between the specs Yamaha calls for.. I'm at .6mm manual calls for .5-.7mm.

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Mr. Robinson Mr. Robinson
11/25/2020 10:48 AM

Cool. I was just noticing the marks where the end gap meets on the back of the cylinder wall and the way it's polishing above the exhaust port.

Are you a pro level rider that really wrings out a 125?

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dfr136 dfr136
11/25/2020 10:56 AM
Mr. Robinson wrote:

Cool. I was just noticing ...more

no haha not pro level. I guess I do ride the 125 pretty hard. I just don't really know what I'm looking at when it comes to reading cylinder and piston wear I'm dropping my suspension off this week to tzr and I am going to bring the cylinder with me. The polishing above the pv is what concerned me and I wasn't sure if its normal or excessive wear.

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Mr. Robinson Mr. Robinson
11/25/2020 11:29 AM

Yeah, cool. See what he has to say.

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LKHill LKHill
11/25/2020 2:45 PM

The exhaust side is fine. The area above the booster transfers is a little scored but should be fine.

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dfr136 dfr136
11/25/2020 2:51 PM
LKHill wrote:

The exhaust side is fine. ...more

I didn’t hit it with scotch brite yet. Is that kind of scoring normal or is there something I need to maybe do different. Thanks

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LKHill LKHill
11/25/2020 3:29 PM

It's fairly typical. Maybe a bit of dirt or a cold seizure. I avoid forged pistons these days for that very reason. You will likely have corresponding marks on your piston

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