Packard Forum Index » V-8 (1955-56)

Yes, the shallow 1-49/64" cups are the correct replacement.

No, the deep 1-3/4" are not correct, but many have survived years of use. One downside is they are much more difficult to remove because the depth hits the cylinder instead of pivoting as do the shallow.

Maybe, since the correct soft plugs are readily available, why not do it right?

jack vines

I'm jumping in a little late here but... I'm in the process of replacing my core plugs and found that Dorman offers two metal types of the same plug, brass and steel. Dorman P/N 565-036 is brass and 555-036 is steel. Both are shallow and 1 49/64" diameter. Is one more correct to use than the other? My thought is that brass doesn't rust so it will last longer, yes, no, maybe?

I think they make them is brass because they don't corrode like the steel ones do. I got the brass. I used Indian Head Gasket Shellac around them, and the hole before I tapped them in. They fit nice, and the shellac will ensure they won't leak. (at least in theory).

If you flush your coolant system out when you're suppose too, the steel plugs last a long time. They deteriorate fast if your coolant is old and acidic.

I will go with the brass plugs. Where can I find "Indian Head Gasket Shellac"? Napa or Knecht's? (The only games in town)

I got mine at Napa.

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I know several successful engine builders who use different varieties of the Permatex line - aviation, #1, #2, Indian Head gasket sealants and also many who prefer silicone sealers. They all have their internal logic.

FWIW, most factory engine assembly line plugs were installed without any sealant. The sealant is for when the holes in the block are rusted or damaged by removal/installation.

jack vines

Perhaps an isolated incident and one for which I have no solid explanation, but I had poor luck with brass core plugs on my 34 Eight, though these are the disc and not cup type. At the engine rebuild I installed brass plugs (even though the original steel ones had lasted 70+ years). Within a few months all but one or two had begun seeping. These are not fun to change as some of them are partially under the exhaust manifold and require removing the manifolds to access them. In any case I replaced them all with steel, used Indian Head shellac as I had on the brass ones, and no issues since.

Since the sealing surface on the disc-type is so much smaller than the cup-type, if I had to guess I'd say the brass discs couldn't hold or retain the compressive force as well as steel and after a short time they "relaxed" in the opening.

I went ahead and purchased the steel plugs. That is what came out of the engine and if they lasted that long then the next time they need replacing I'll be history. Here's an FYI for the next guy, there is a freeze plug, 1 3/8", on the back of the water manifold. Mine looked just as corroded as the engine block plugs.