I have some 320 grit lapping compound and was thinking about lapping all my valves on my GT40 heads just to improve the seating. Any suggestions? Other grit? etc. No, I cannot afford a "real" valve job right now...
With the heat that was put into the seat from welding up the port, I would definitely have it re-surfaced.
I agree, but if you have a lot of time and energy, you can do it by hand but not recommended. A courser grit compound first, some dykum bluing on the valve(to check for seat contact pattern etc.) Guide wear will also affect the sealing abilities of the valve too. Many moon's ago when I raced stock cars(32 to 46 models with mild sm Fords and Cheby engines) a good performance improvement was to run 498 lift factory solid lift cams, with stock rocker arms and 2 barrel carbs. Limited funds dictated such things as a small can of model airplane fuel mixed with the gas(lot's of nitro content back then) and put one .060 valve spring shim on each of the 16 springs. Really helped seal up worn out springs and valves, that is backyard racin but worked on everything but the Ford flathead and mopar flat six bangers. Couldn't or won't do it now though, modern equipt. and choices of springs and valve angles is the norm these days.
Luckily, the weld was at the other end of the port, but you never know how metal will react to that kind of heat... Thanks for the input.
When you lap a valve against a seat you make the seat and valve contact area larger and larger. You also destroy the interferance angle that cleans the valve while it is running. (seats ground at 44* and the valve is at 45*) If you were doing this to a performance engine I would say NO!!!! but since it is a daily driver street car then go for it. Check it for sealing first with some Prussian Blue. If it isn't sealing then lap it just enough to get it to seal. You might as well check all the valves while you are there. There is no point in doing all that porting and then have a leaking valve.
