Valve Seal replacement


Oct 12, 2004
Based on my post in Chit-Chat, it sounds as if the valve seals on my 1979 4x4 pu w/ the 20R might be bad. The truck/engine only has 37,000 miles on it but it was a plow truck, so it sat for long periods of time. IF the valve seals are bad, how hard is it to replace them? What are the steps involved? How much should I pay to have someone do this job fro me?

Thank you,


Frame waxer
Apr 5, 2003
Southern NH
I read your post over there, I'm not convinced that it's the valve stem seals. However, with those few miles I wouldn't be surprised.

I would first do a leak down test, make sure the rings and valves are good.

If the stem seals are infact leaking, you won't be able to tell by looking at them. And besides, in order to see them to inspect them you have to pull the valve springs off, and by the time you go that far, you might just as well replace them, they are pretty cheap to buy. Do NOT use aftermarket seals, go OEM!!

I suppose it is possible to replace them without pulling the head, but I'm not sure it's a good idea. You have to pull the rocker rails off, and this requires removing all the head bolts. Then you have to figue out some way to keep the valves from falling down into the piston with the keepers and valve springs removed. Not sure a reliable way to do this, without spoiling the head gasket.

Buy the OEM head gasket kit, it's about $100, pull the head and do it right. There's a double-chain in that engine, no need to replace it with that few miles. But be prepared to have to replace every single seal and gasket in that truck eventually, expecially in the brakes. The only thing worse than driving the hell out of these trucks is not driving them at all.
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