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8/29/2018
Location
Union Bridge, MD
US
m1ke20012
12/5/2018 2:47pm
12/5/2018 2:47pm
Edited Date/Time
12/27/2018 10:59am
Can anyone tell what is causing this? This has happened twice. I got the bike like such and then Replaced the top end for it to do it again 4 hours later. I was told it could be detonation and running lean. Bike is an 03 yz125.
The Shop
I would be looking at trash in the crank cavity.
Excess piston to cylinder clearance.
Old fuel mix.
Not allowing the engine to fully warm up prior to putting it under heavy load.
Did you check the squish?
Paw Paw
there are also a few threads on the net about pro x pistons breaking exactly like yours.
https://www.google.com/search?q=pro+x+piston+broke&ie=utf-8&oe=utf-8&cl…
exactly what do you mean by running hot?
exactly what was the piston to cylinder clearance?
exactly how did you measure the clearance?
can you post a photo of the end of the spark plug from a slight angle?
Check check double check all the details. Don't assume a shop bored it with proper clearance...check it yourself,,,don't assume piston top isn't too close...check it all the way around with clay...I have seen pistons tighter on one side...Don't assume main bearings are good cause they are new...check them up and down with rod.
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i would use a different brand of piston.
check the squish clearance and make sure the skirt is not hitting the crank.
not necessarily.
ok, explain in detail exactly why you think it ran hot, ie, hotter than normal.
Pit Row
STOCK YZ125
Do you have a temperature gauge?
Were you going full throttle up a steep hill?
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