Overheated my techno. Piston, barrel and compression all Ok, but waters getting forced out of the rad cap. Took the cylinder head off and you can see that the o rings have pushed into the damaged areas letting the exhaust gasses in/water out. Anyone know of a way to fix these damaged areas as a new cylinder costs more than the value of the bike?

A good engineering workshop could weld it and re machine it

Some chemical metal or epoxy filler should make a decent repair of that

Agree with #3 but make sure it is a GOOD engineering shop preferably one that is used to head / barrel repairs.

Aluminium contracts a lot on going from liquid to solid.

The barrel will need uniform preheating and controlled cooling along with a minimum heat input welding technique to allow contraction to take place as the weld proceeds and then finish on a run out plate.

I have seen successful cylinder block repairs with epoxy but would not try on a thin edge like your beta barrel.

Edited January 22, 201511 yr by dadof2

The root cause of your problem isn't that the o ring has failed, rather the compression joint between the cylinder head and barrel has failed, the neoprene/rubber o rings job is only to retain water and not to contain compression. If it's possible to lap the head to the barrel, to recover the compression joint, then as previously stated jb weld or similiar would probably be OK for the low pressure o ring water joint.

Edited January 22, 201511 yr by ask greeves

How deep is the damage? If not too deep, you may be able to remachine the top surface of the barrel including the o-ring grooves. It would be a simple machining task. You would then run a thicker base gasket to compensate for the shorter barrel. This would alter the port timing a little. A head spacer as sold in the past to reduce compression and soften power would be another way to compensate for the height and it would not alter timing. (I ran a 1/16" head spacer on my daughters Techno with good succcess.) If going with a thicker base gasket, you would want to make sure the threads in the head were still deep enough for the bolts. Worst case, you could run 2 copper washers on each bolt.