valve hardening

[mburgess]

I am rebuilding a small 4cyl Kawasaki motorcycle engine for road racing and I am trying to track down knowledge on surface hardening of the valve seat of the valve. The valves are a two piece (bi-metallic) design with a single 45deg seat. I wish to backcut the seat however I am unsure how this will effect the durability of the valve. Will this cause the hardended face to flake away (especially in the exhaust valve) or can valves be de-hardended, backcut, refaced and hardneded again??
Any help would be appreciated.
Michael Burgess

 

[andyv8]

You should be okay to backcut the valves as long your machinist of choice uses hard turning which shouldn't damage the hardened area.
I've run engines with the valves back cut (intake and exhaust) into the hardened area and didn't find any problems after 500hours on the dyno.
One thing that you really must be careful of is not to reduce the valve seating area so that it is narrower than the valve seat 45° angle at any point. This will rapidly lead to high stresses in the valve head which will then (probably) fall off.

Andy

 

[mburgess]

Thanks Andy.
Regards
Michael