new bike, yz125, blew it up

Joined
May 6, 2013
Likes
69
Location
Portland
#1
Picked up my first dirt bike, rode it a handful of times and blew my top end. Can anyone tell what happened based on these photos? No idea on the prior owners maintenance or when the last time it was rebuilt.

IMG_0046.jpeg
piston.jpg
cylinder.jpg
 
Joined
May 6, 2013
Likes
69
Location
Portland
#6
Thanks for the replies, the crank seems fine but i am not an expert. it spins freely, no noises or grinding at all. looks like a chunk was taken out of the cylinder wall
 
Joined
Jul 12, 2017
Likes
5
Location
New Zealand
#7
You're that far into it now, get the crank checked if you arent sure. Bottom ends dont always make noise but if its worn enough to give even a fraction of a mm movement it will end up being a bad, and very quick, first ride after the top end rebuild.
Was anything missing or broken when you pulled the piston out? Ring, clip? Something rattling around and could easly now be in the bottom end.
Nice bike, good luck sorting and getting back out soon.
 
Joined
Jun 9, 2015
Likes
2
Location
Australia
#11
I have had a few YZ125s. Favourite bike would be the last of the steel frames for sure. Piston rings smashed up I would say.

My advice would be to have someone who is in the know look at the crank. If it checks out run it.

Have the cylinder sleeved also. Safer than running into more trouble with a plated cylinder.

I had a sleeved to 133 (?)cc 2003, mild porting, knife edging and clean up, with a pipe and honestly ran so good for so long. The plating is technically better, but if you are a casual rider or local racer it's not worth the extra 5% IMO.......
 
Top Bottom