OK so I know in the OEM world valves and seats are machined and assembled with no lapping (high precision machining of the components to minimize tolerance stack up). However in our world should we hand lap the valves after grinding. I ask only because I just installed a head I had rebuilt into one of my 2004 R53's and the intakes grossly leak to the point I pulled the head again and will return to the machine shop tomorrow. I suspect they do not lap but will confirm that in the morning.

 

You should not have to hand lap the valves on a fresh grind. Machine shop should be able to correct the problem. They might lap them to correct your issue, but a normal grind on both should not leak significantly. How did you measure the leak? You might want to do a leak down test.

 

Used a leak down tester and saw 50% leak (worst one) prior to holding palm over intake port (that was not easy at 85psi test pressure). Once I was able to seal the port she dropped to less than 20% which I can live with (168K miles on this one), engine was around 5° C so would expect this to improve when normal running temp. Was not able to get over to the shop today, will have to wait till Saturday (I may just lap them in myself, at least I know it will be done).

 

[QUOTE=Domiracer;3907095]OK so I know in the OEM world valves and seats are machined and assembled with no lapping (high precision machining of the components to minimize tolerance stack up). However in our world should we hand lap the valves after grinding. I ask only because I just installed a head I had rebuilt into one of my 2004 R53's and the intakes grossly leak to the point I pulled the head again and will return to the machine shop tomorrow. I suspect they do not lap but will confirm that in the morning.[/QUOTE

Make sure the machine shop ground the seats in the head the same angle of the valves. I say this because when I worked for GM in 1966 there were 1,500 Oldsmobile V-8 engines built with 30 degree angles ground on the intake valve seats in the head, and 45 degree valves installed. Had about the same leakdown percent you're talking about.

As for lapping in the valves I've been doing it since the 50's when I was working on flathead Ford V-8's. Lets you see how wide the sealing surface is on the valve. Some things don't change over time!!
Edit: I would add that leakdown any more than 10% is suspect. I've built engines with leakdown as low as 3% when first assembled!

 

Bust out the prussian blue paste and see how the seats are.

 

i always lap my valves, always.... whta i do to make it go a little quicker is i put the compunound on the area, then attach the hose the the valve stem then the other end of the hose to a drill, i can control speed and pressure on the valve like this, and it alwyas comes out great.

 

Decided I will tear into the head tomorrow and inspect the valve grind and seats before heading over to the shop. I could understand the leak if the guides/valve stems were worn but guides were replaced and stems mic'd to spec. I will blue the seats and check contact to valves and go from there. Based on what I find I may just lap them in and move on (use a different shop next time). Hopefully this one will back on the road next week, just in time to pull in my sons R53 for a new clutch, any recommendations on a good general duty clutch. I have a spare Dual Mass flywheel being fixtur'd for a resurfacing test, hopefully that goes well, anyone done this?