CRF's Only Forums

hi all . im new to the forum and thanks for having me..

ive rebuld my crf 250 r from the ground up as it dropped the big end bearing out on me. anyway i went to start it today and started fine. sounded fine. but when i went to rev the bike putting it under load. i could hear a loud cracking as though there was a blow direct from the exhaust manifold so i looked down the side of the engine to confirm but it was not coming from the exhaust it was spitting out the side of the bore where the headgasket is.... baring in mind a brand new headgasket kit was fitted..

has anyyone seen anything like this before?
do the heads have to be skimmed prior to a new gasket fitted? both surfaces were thouroughly cleaned.....

theres no oil or water leaks ....
no mixing of fluids...

any help would be greatly appreciated

thankyou for reading

That's a bummer. The bike is telling you that the mating surfaces aren't flat. There's no rule that anything needs to be resurfaced when it is taken apart, it just has to be flat. Hard to say if it is the cylinder or the head, although I would bet on the head.
It is going to have to come apart again, and all surfaces checked for flatness.
Any chance that you wedged a dowel pin in sideways and it is keeping things from mating?

thanks for your reply mate..

yes im going to strip the headback off today and inspect further.

here i s a pic of the direct location where it blowing out flames and sparks lol