Both the my one original and one new (used) head are warped a little. I know that the original has been resurfaced before, and am not sure about the other one. I will resurface them myself with a flat glass pane with sandpaper glued on. I know this sounds like a bad idea but I have done it before with success on an aluminum Volvo engine. I also want to lap the valves (not sure if I should). However I am concerned that valve lapping in addition to the resurfacing will cause clearance problems. Will this happen making be need rocker shims or will the hydraulic tappets counteract this?

 

You'd need to remove far more material than resurfacing and lapping is intended to for it to become a problem.

 

A bit risky to use the glass and sandpaper method, in my experience can make things worse. Use a real machine shop for a sure bet to true up the heads and get the correct surface roughness and you won't be sorry.

There is a method published to check lifter pre-load gap when assembling, so proper shims can be added under the rocker stands. Shims will likely be needed to compensate for the machining, to ensure valve lift and timing will be correct.

No problem lapping valves. Good to do while you are in there.

 

I have used the glass/sandpaper method on a volvo head and it worked great. What would be the problems you were thinking could happen.

 

If the surfaces end up uneven, or the edges get rounded, then the head gasket won't seal properly. Even incorrect surface roughness could cause sealing problems.

Remember a tank of gas costs nearly $100, OK $80. So machining properly is a simple and good investment.