Hand-lapping valves

[Dakotakid]

Fine, here is a new post. Pardon me if the answer to this question is overly easy.

I had one of the local machine shops (very good reputation, even with the few guys I know who drive VW's) install new valve guides and then use their rather expensive machine to resurface the valve seats. Before you ask, they did pressure test the holes after the work. All this runs into money....don't it?

I purchased all new TRW valves (hydro head) and was busy hand lapping them and inspecting my results with my magnifying goggle/glasses.

My question: When can I stop with the lapping? Just how wide do the gray bands get on the 45 degree (seating surface) aspect of the valve?
Is there ever a time when these new valves will reach gray across this whole surface???

I recently hand lapped all the used valves in another fresh looking head which did NOT get the rebuild treatment as the head above. When I lapped the used valves, I recall that I achieved a gray surface across the whole 45 degree aspect of the valve. No, I have not had the chance to put this nice looking used head to service yet.

Common sense tells me that the more surface area (gray area after lapping) that you achieve......the better your seal for the cylinder and the more optimal heat transfer you will achieve. Right???

So, tell me about the original question re: these new valves and refreshed seat. I started with fine paste...then elected to use the more coarse paste. Then finished with the fine. My exhaust valves are gray in about 65% of the surface and the intakes are at about 60%. My seat surfaces look uniform under close scrutiny.

[Smokey Eddy]

i gave up lapping new valves to a new head once about 2/3rds were grey. it just got really easy to spin them after that so i thought they were good. (or wouldn't get any better without a LOT more work)

[klr4evr]

With lapping you are trying to get a perfect match between the valve and the seat. Maybe I'm misunderstanding what you are doing but I wouldn't be trying to get 100% face contact between the valve and the seat. You should  lap the valves until you see a decent seat being formed on the head and valves, until the valve and valve seat are a uniform grey. I lap until there is an even width band around the whole valve showing that there is full contact with the head. The area of contact between the seat and valve can then be checked with Prussian Blue or a machinist's lay-out blue to see if any additional lapping is required to clean up any gaps that may be left. You don't want to take off any more material than you have to.
Lapping isn't too common anymore with modern valve refacing equipment. You said you had a shop resurface and pressure test the holes. That should be sufficient.

[Smokey Eddy]

aye aye.
The last time i lapped valves they were for a small block and we used a blue felt to see how much transferred from the valve to the head to see how well it sealed. When a complete circle was formed it was enough.