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Re: Silicone Valve Cover Gaskets and Some Saab Status Posted by eric in vermont [Email]  (#2058) [Profile/Gallery]
(more from eric in vermont) on Tue, 29 Nov 2022 04:02:13
In Reply to: Re: Silicone Valve Cover Gaskets and Some Saab Status, Charles, Mon, 28 Nov 2022 17:50:30 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Good questions...
Answer to the first: no. True valve lapping is a process in which an abrasive valve lapping compound is first applied to the valve/head mating surface. Then the valve is twisted back in forth with pressure against the mating surface. The result is a very smooth, tight, sealing surface between the two parts, head and valve. So with the valve in the head, there's no way to get lapping compound in there, and there's no way to get it out if you DID somehow get it in there.
All that said, a backyard mechanic *might* try this: remove the valve rocker and the spring, chuck the end of the valve up in a drill, and slowly spin it while it's in the head. It *might* restore the mating surface enough to restore compression. I'd view this method as temporary at best, if it works at all. Or it might work if there's a piece of carbon stuck in the mating surface. If the valve is truly burned, which I suspect, the lapping process even done with the heads off, won't restore the surface. The ones I've seen have mushroomed valves that even machining can't fix. New valve and new machined surface is the only remedy. So if you want, on the off chance that it is a piece of carbon, pull the valve cover, make sure that piston is all the way up so the valve doesn't drop out, remove the spring, chuck it up and give it a spin. I don't think you can hurt anything.
Answer to second: hardened valve seat installation for the exhaust valves is a standard machine shop procedure. If you were to get the heads rebuilt (maybe along with the whole motor), you would instruct the machine shop accordingly. Note: it's only needed for exhaust valves because of the high temps of the exhaust gasses after combustion. Intake valves don't need it because the incoming mixture is much cooler.
One more thing comes to mind (thinking of your Dad). You CAN change the valve seals in a Saab motor without taking off the heads. This is done by using compressed air blown into the spark plug hole with a special fitting to hold the valve up in place. I've done that on several Saab engines over the years because the umbrella valve seals get hard and crack. If you pull your valve cover, you'll likely find pieces of hard, black stuff floating around. Don't panic- just the valve seal pieces. You'll use a little more oil, but not a big deal. Main symptom is smoke on startup. Maybe he was thinking of that process?
eric in vermont
, Sat, 26 Nov 2022 13:34:48
1, Mon, 28 Nov 2022 10:21:57, Tue, 29 Nov 2022 04:02:13 <-- Viewing This Message, Thu, 1 Dec 2022 05:32:10
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