Maximum lift?

Can somebody give me a ball park figure for the maximum valve lift a stock J head will handle before you need to cut down the guides? I seem to remember reading way back that it was around .510", but I'm old, so my brain doesn't work as good as it used to. :sad1: How much clearance is required between the top of the guide/valve stem seal to be safe?

I think I have built up to the .540 range and that is close. i think you are correct i read .510-.520 for stock guides, and you need at least .050 for float too.