Please help i've recently brought a dt 125, and after having a look over it i decided to have the barrel rebored .

after refitting the new piston in the rebored barrel and starting it up. it ran nice on tickover untill abit of throttle was used and then pop. removed the head/barrel and i now have a smashed piston , so purchased a new piston checked the port edges for smoothness replaced everything again started it up. again tickover fine a few revs and then pop . any ideas guys

regards liam

What do you mean by "smashed"?

Could it be that your Con-Rod is bent?......& did the piston break inside @ the wrist(gudgeon) pin?

Or do you have a hole in the top of the piston?....which could mean that you've got a serious air-leak somewhere causing it to run really lean & resulting in the "pop" you spoke of.

Please help i've recently brought a dt 125, and after having a look over it i decided to have the barrel rebored .

after refitting the new piston in the rebored barrel and starting it up. it ran nice on tickover untill abit of throttle was used and then pop. removed the head/barrel and i now have a smashed piston , so purchased a new piston checked the port edges for smoothness replaced everything again started it up. again tickover fine a few revs and then pop . any ideas guys

regards liam

I assume that the rings were fitted correctly ie right way round and either side of the locating pegs. Did you have the ports opened?

I am thinking the rings expanded into the ports causing the mayhem!!

I assume that the rings were fitted correctly ie right way round and either side of the locating pegs. Did you have the ports opened?

I am thinking the rings expanded into the ports causing the mayhem!!

yes the rings and pegs located correctly, no the ports have'nt been opened by me perhaps a previous owner/s did ? the piston damage is on the inlet side of the piston in the skirt area and no there is no hole in the top of the piston would a badly ajusted power valve cause a piston to jam ?