valve seating

[Glenwood]

I could use a bit of guidance regarding a set of 906 heads I'm working on...

I bought a set of 906’s sometime ago for my 413 build, because they supposedly had already been rebuilt and had about 10,000k on them before the owner had aluminum's installed.

I’ve torn them down to clean & inspect and I can see that they have hardened exhaust seats installed as well as bronze guides with some milling on the guide ‘bosses’ to accept double springs I guess. The intake valves had a good amount of carbon and oily soot like build up on them, which makes me leery of the guide clearances. They seem tight to me, but I don’t know how to check them properly. I also checked them for flatness and they are .002 or less, so I’m thinking they should be fine for the thin head gaskets I intend to use.

I gave them a good cleaning using a scotch-brite pad and reassembled. I did a leak test with varisol and all valves are seeping slowly. The exhaust valves were seeping noticeably first, but very little over a few hours. Overnight, the chambers are still half full with the intake runners having a little solvent leaked into them now. Do you guys think these need regrinding to seat properly or does this seem to be an acceptable rate? I’ve read that lapping is not recommended by engine builders.

 

[miller]

I’ve read that lapping is not recommended by engine builders.

I suppose there are various views on lapping valves. It's something I've always done, mainly on new cut valves, and seats...but, only using fine lapping compound, to verify a full contact seating. With the heads tore down, as you have them, is the 'only' time I'd do it, with a good washing after, on all the parts.
Only other thing is, when a valve is lapped to a seat...that valve needs to go to that seat, when you put it together.

But, gotta add, I do not use compound, to 'cut' the seat/valve, only to check. Might be worth while to get your machine shop to 'freshen up' them. That's what I'd consider.

Hard to say on your guides. Personally, believe the best way to 'measure' them, is using go/no go gauges. Though that's something might have to be made. (Just stepped gauges). Usually, exhaust guides get the most wear, should be checked at the bottom of the guide, where they take heat.
Not much use starting out with worn heads.

 

[Glenwood]

Thanks Miller. I should add that the valves were reassemled in the same locations that they were removed from, yet they are seeping. Probably were before but I didn't check before disassembly.

 

[66Satellite47]

I've used lapping compound many dozen times. You can use a magic marker or machinist dye on the seats, the work the lapping compound to check the seat pattern. That should show flaws in the valve job. That does presume the guides are pretty good. The pro machine shop has the tooling needed to check guide clearance. What type valve seals do you have? That's a frequent cause of the buildup on the valves.

 

[Glenwood]

The seals were the tight fitting rubber types, likely felpro or similar. I found it interesting that they wer also installed on the exhaust valves as I thought these either were supposed to be the short umbrella type or none at all. How would the exhaust valve stems get oiled with tight seals?

 

[lewtot184]

'906's use the full umbrellas on intake and exhaust.

 

[miller]

So...the heads have 10,000 miles on, since last worked, and the valves are slightly leaking. Plenty of options. Really up to you, deciding how far you want to go, and how many miles you want to get out of the build.
Personally, I'd have the machine shop take a look. But, added to that, looking at them now, do they have 3 angle-cut seats? Another lame thought, is if you want better guide seals installed...that takes cutting the tops of the guides. That stuff makes the machine shop your friend, lol, as long as they know what their doing.
Back to the seats, for a second...ideal seat is 3 angle...1/8" wide actual seat to valve, upper half of the valve face.
Also measure each valve stem, to be sure there's no, or little wear. Then, the guide clearance...on, and on. Heads can be made as good as you want them, or just get you by.