1990 RM250 crack in exhaust port on head

[grayman19]

1990 RM250 crack in exhaust flange on Cylinder!!!!!

I was leaking a lot of oil out of my cylinder where my exhaust goes into it. So I went and bought a top end gasket set to replace the gasket. To my horror I have a crack in the flange the pipe goes into. Does anyone know a place I can send this to for fixing? Can it be fixed? Should I buy a new one? If so where should I go! I know this is lame but would jb weld work? My neighbor is a welder and can weld it he says but is extremely worried about warping the entire cylinder if it gets to hot. He said aluminum conducts heat way to well and could pose a problem. Help!

 

[BJAWES]

Exhaust port or head? The head is the small dome on top and has only a spark plug in it. If you can get him to weld it for you i'd say do it. It won't be a problem if the head doesn't get warp alot. I have a 1 foot by 1 foot piece of flat board that I staple 220 grit sand paper to, and use it to take warp out of heads. Just put the head on the board and move it in a circular motion, flip the head over and check the sealing surface often, you should be able to see the high and low spots. In the event you take off more than an 1/8 of an inch, you will need to buy a new head. I've used this trick to bump up the compression (more bottom end) in both 2 and 4 stroke engines. It is always a good idea to kick the engine over slowly at first and feel the amount of compression you have before you start the bike, if its to high or to hard to kick DON'T START THE MOTOR. hope this helps- bjawes

 

[TravisP]

Please Please do not lap your head on a piece of wood it is no where near flat enough send it to a machine shop they should have a granite block or even plate glass but dont use lumber!!!! if your exhaust is leaking it is caused by a coulpe things the rubber bracket that holds it was loose and caused the manifold to crack loose motormounts dont just fix the symptom find the cause.

 

[BJAWES]

Notice I say "flat" wood, my desk is made of oak and it is very flat you couldn't squeeze a small feeler gauge between it and a straight edge, speaking of that you could use a straight edge to check for warpage also. The piece of wood that I use and have used several times works great. True, a machine shop does not use wood but thier goal is to make a flat sealing surface, that is where a straight edge would come in handy. I've been a tech for 13 years and I'm currently one now, I don't do quick fixes or hack jobs either, all I can to is tell you what works for me. sorry for any confusion- bjawes P.S. Travis may be right as to how the head got cracked in the first place.

 

[grayman19]

Ok guys, I am sorry I meant to say cylinder. My head is fine! How hot does the exhaust exit the head? Please do not argue with each other, advise is always good! :aj: