Lapping valves & valve stem oil seal replacement

Hi. Not directly related to this tutorial but I am going to be replacing the valve stem oil seals and lapping the valves on my duratec cylinder head. Should I replace the oil seals first then lap the valves or lap them with the old oil seals in place then replace them after lapping?

The seals aren't really relevant to the lapping process as the valve is supported by the guide so it's not really that critical. If you haven't yet replaced the seals then I'd lap first but wouldn't let it stop me if the head had new guides. Keep in mind that valve lapping is a mixed blessing. I only use a light lapping compound and just perform a very light lapping to remove any marks from the cutter. If you alp the valves too aggressively you'll end up with the valve only sealing when the engine is cold.

Thanks Andre. Very helpful. I’ll do a light lapping first then replace the seals. Just need to clean up the mating surfaces a bit. Nothing too drastic.

Hi Andre,

was just thinking - were you referring to lapping new valves?

I’ve cleaned up the existing valves which I’m looking to reuse so want to clean up the valve to seat mating surfaces to ensure a good seal. Would you still recommend using only a light compound ?

Yes, regardless whether you're using new or old valves you only want to lightly lap the seating surfaces. If you go crazy with a coarse abrasive you'll end up with a concave seating surface that only seals when the engine is cold.