The Stovebolt Site Forums The Shop Area Engine Shop Uncooperative valve cover

Trying to get my new valve cover gasket to seat properly. There's too much slack on the front and back end. And I've gotten 3 different grommet sizes for the acorn nuts. The smallest gets chewed up before the valve cover makes contact with the head. The larger ones get mushroomed. Before the rebuild, the valve cover was plastered with silicone, Is a double gasket a bad idea? Any insight would much appreciated.

I'm afraid your valve cover has been tweaked too much to fit well. You may be able to straighten it enough to seal with some hammer and dolly work and a flat surface to use as a reference point. A double gasket would just make it bend more. It may help it seal, but is just a band-aid.
Take the valve cover off and lay it on a flat surface and you'll see what I mean.

Thanks Kevin. This ought to be fun.

Yup, it takes a lot of patience and time to get it flat on the bottom. About the same poor manufacturing as the 260,289,302 Fords. The big part of this equation is suffering messing up a great paint job. It HAS to be completely flat. As for the top washers I use a white silicone grease so the nut won't wrinkle. One has to suck it up and sand down, prime sand then repaint. I feel your pain. Doc.

I don’t have a 228 style valve cover but something seems amiss here. The acorn nut appears to be too narrow where it contacts the grommet so it has no choice but to slide into the grommet. I would think there should be some sort of washer keeping the nut on top of the grommet so it has a chance to apply pressure to the gasket.

Maybe some of the experts that own 228’s can chime in here.

There isn't any gasket for the valve cover nut. The tapered nut is the only seal.

Joe

The last 228 I had (a 1951 model) used a rubber grommet which was a stepped affair (larger on the part which sat on top of the valve cover and the smaller stepped part fit snugly right inside the valve cover hole and was a fairly tight fit on the mounting stud), then on top of that was a flat washer the same size as the diameter of the grommet and holding it all in place was an acorn nut which if you had a new gasket and new grommets would only catch about 3 or 4 threads of the mounting stud before it started getting tight. And you didn't want to tighten it too much or you would mess it up. There was no tapered nut anywhere on mine, but maybe something changed between 1949 and 1951. That is my guess. Parts stores sold those grommets and when you bought them, they often also included new washers in the box. The acorn nut and that washer pushed the grommet down tight on the valve cover and in turn pushed the valve cover down on the head. Then there was one gasket about 5/16 inch thick glued to the valve cover and as already mentioned the surface of the valve cover needed to be very flat and at right angles to the vertical part of the valve cover...that was important. If it wasn't all straight and right, it would leak cheerfully. If you glued 2 gaskets to the valve cover, you never would have been able to start the acorn nut. Even if you did everything correctly, it was likely to leak after a few weeks.

I’m not sure these GMC ‘s had an acorn nut to begin with. Most of the GMC’s that have come through the door have a stepped or tapered hex nut. The aftermarket grommets fit like you are experiencing. I have used a thin SS washer on top to help seat. The grommet just helps seal the gap between the threaded rod and the cover. Just torque the bolt or nut enough to seal and catch as many threads as you can... or turn out and raise the threaded rod enough to secure that top hex nut or acorn.

But yes, start with a flat cover... read the manual. It may say use a silicone type sealant on the cover and gasket. Or the cover may not use a sealant. Can’t remember what the manual says. I use Ultra Black and lightly place the gasket into the cover after letting it set up for 10 minutes. Then I lightly press the cover down with nuts, wait 10 minutes, then do it again. Maybe overkill but it seems to allow the gasket and sealant to mold to any irregularities.


Repainting is just taking time to do it over. Call it a casualty of the war.

BTW - nice paint job. What paint did you use? I used Jim Carter green for the early GMC’s but it laid down glossy. I like the flat paint.

Thank you all for the input. The the manual doesn't seem to address grommets at all. It's mind boggling, but it makes sense that the tapered nut has no grommet at all. I sent it to the rebuilder without pulling the valve cover. (Shame on me) As for the paint, I started with Rustoleum satin black. I added green, yellow and blue until I was happy with it. I thinned it with reducer and sprayed it with a small Binks gun.