In the past we have straightend heaps of valves from stainless to titanium and the steels that nc cams has mentioned simply because our customers could not afford new valves, most of our stems are from 3.5mm to 8mm thick.As a general rule if you can see more than 1mm of light between the seat and the valve face it should not be done ,and definitely do not hot bend them .I use a large alluminium block with a hole drilled in the side of it to suit the valve stem and tap them with either a small alluminium hammer or plastic.Try and keep the mushroom part of the valve as close as possible to the block.We use a very small v block with a end piece to stop the valve from moving back to far and a dial indicator to check for truth,when true we lightly grind them to spec.So far we have had no failures at all, but like the guys in this thread have stated if there cheap enough you would be silly not to buy new.I hope this helps greg b |