I'm using 906 heads on a 440 and ductile iron rockers and seem to have a interference with the casting flash and 3/8ths pushrods. Is this common? I assume I can just take the head off and carefully grind down the flash? What is the minimum pushrod to head clearance?

Thanks!
Paul

Common. There is no "minimum" but ten or fifteen thou would be nice. Any more won't hurt as long as you don't grind into water or a port.

Depending on what spring and how aggressive the cam, I bet at 0.015" clearance you will see witness marks on the pushrods. Not saying that's a bad thing, but I believe they flex a lot more than people think.

R.

OK sounds good thanks for the help!

I use different thickness rocker arm shims, they come in .015, .030 and .060, to space the intake rockers away from the intake ports on the heads and to help center and align the rocker arm tips on the valve stems IHTHs

What Dog said, I'd want more, for me maybe 30 tho at the closest point

Just remove the heads and ream the passage out for your clearance. It isn't rocket science.