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Piston Skirt broke, 2nd time.

By ScrewMx_Hd,
in Honda 2 Stroke

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Grand Master

ScrewMx_Hd

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2nd time in a row this has happened. OEM piston with about 26 hours of woods racing. Running 50:1 with amsoil dominator, Didn't snap a pic of the cylinder, looked fine, nothing caught with a fingernail. Rebuilt Bottom end about 24 hours ago, when rebuilt had a small top end noise that we never diagnosed, would be an on and off noise. Never had a problem before this. Ask any other questions and i will answer, just trying to find out if this is a common problem with Gen 3 Bikes. Bike is an 06 CR125 IMG_0778.PNG

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slotracer577

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What's seizes the rings??

 

Oil can gum up the rings, detonation might damage the ring lands, but more so on 4-st with short skirts, large exhaust ports beat the rings up when they move into the port, then get slammed back into the piston. On the road race cylinders which have huge ports you could need to dress the rings after every session.

As mentioned above piston slap probably did in the piston. Check the clearance and also check the cylinder to make sure it's not out of round.

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Grand Master

shrubitup

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3 hours ago, ScrewMx_Hd said:

forged pistons are very prone to cold seizures if it isn't warmed up properly right?

Proper warm up only takes maybe five minutes then another five minutes of easy riding then rip for rest of day. 

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peaceofwork

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i dont know about that surubi, i been getting away with a start-up flip the choke off imeadiatly then give it enough throttle to keep it running for maybe 30 seconds then shut it down and get my gear on. after that restart it run it maybe another 30 seconds then head out gently no more than 1/4 throttle but dont lug it and pull a few gears easy dog around a couple min then wack it . any studder or hesatation back off and let it warm up a little more and hit it again is my weisco warm up procedure for the last 20 years.

I  forgot to say a torque plate is used on my cyl for bore and hone work so that makes it break in and tolerate abuse nicly

Edited by peaceofwork
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Smokin CR 125R

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NOT a Common Problem with Gen 3 bikes..........

Hyperutectic cast piston and 50:1................That is what is going to happen.....

50:1.......Very bad Idea with a high RPM 125...............

Edited by Smokin CR 125R
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Grand Master

ScrewMx_Hd

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NOT a Common Problem with Gen 3 bikes..........
Hyperutectic cast piston and 50:1................That is what is going to happen.....
50:1.......Very bad Idea with a high RPM 125...............

Bike was not ridden as an MX'er, mostly a down low clutched along woods bike.
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Grand Master

shrubitup

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Bike was not ridden as an MX'er, mostly a down low clutched along woods bike.

Since you race it and want to rely on it you should try a piston at 32:1 just to appreciate if there's any difference. For slow trials like trail riding you can get by with less oil.
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