I am just finishing up the restoration of an Edmunds dual two barrel intake manifold for an Olds Rocket. There are three holes that I won't be using that I need to plug, one is 1/2-20, the second is 1/2 NPT, while the third is 3/8 NPT. The plugs that came in it were regular iron pipe plugs and were rusty. I cleaned them up, but they're not gonna do it. I was considering br*** plugs, but became aware that there are also aluminum pipe plugs available, as well as stainless steel. The aluminum plugs come with an Allen head and I think that they would be the most unobtrusive looking. For some reason, I am thinking there may be a problem with aluminum threaded into aluminum; expansion, fusing together? I really don't know. Anyone have any insight to this?
I'm no metallurgist but using aluminum plugs in an aluminum casting shouldn't be a problem. I'd tighten them just enough to not leak. Let the taper do the sealing. I'd use teflon tape applied correctly or pipe dope with PTFE or even a light coat of the dope over teflon tape. We did that especially on large fittings in high-purity water applications. I guess you've verified that the one hole is indeed 1/2"-20 TPI? That's going to take some sort of seal, washer, or O-ring since it wouldn't have any taper to seal when snugged in. The aluminum (AN) plugs can be found at typical performance sellers or likely through Grainger or McMaster-Carr (Ugh!) Lynn
If they are not anodized, threaded aluminum plugs will most likely seize in the aluminum hole. If they are anodized, they should be OK. Are you trying to make it look like an old hot rod? If so, use what was available when the manifold was new. That most likely means iron plugs.
If not plaining to use ports I would look for extra long pipe plug aluminum or make after installing I would file sand top off flush to intake , it would have a slite line more appealing to eye? I would just lock tight , In future you would have to drill out but you can pick up cheap pipe taps @ Harbor Freight . I reclock many pipe threads to lower the fitting from stick out to fair
Having dealt with this many times in my work life, I can tell you that aluminum/aluminum, aluminum/stainless steel, and stainless steel/stainless steel joints are the worst for seizing if ***embled without some sort of anti-seize. I have literally spun stainless nuts onto stainless bolts with my fingers and have the nut seize to where it would break the bolt trying to get it off. The same for aluminum/aluminum. My recommendation would be stainless plugs with teflon tape or paste. Aluminum plugs can strip out too easily. Don't skimp on the paste if you use that.
How so true on stainless !! ^^^ Just snug one down, 10 minutes later go to remove after verifying fit of parts and the damn thing be locked up. Thought about using stainless bolts with standard nuts, thought about it but never got any further with that train of thought... ...
If they are to be permanent I'd use aluminum plugs potted in JB weld and ground off flush. If temporary then stainless with pipe dope or teflon.
Galvanized metal has the lowest risk of galvanic corrosion. You could use aluminum plugs but want to match the alloy. I wouldn’t use stainless.
You could have the br*** ones nickle plated. If you do not want br*** to show and they should come out easy later.
I screwed up once and won’t do it again. I installed an aluminum plug in my aluminum intake. Big mistake. Seized tighter than tight. I had to drill it out and retap to larger size. I used a br*** plug and had no problems.
This is the sorta thing I was afraid of. It looks like it's either br*** or iron. At this time. br*** appeals to me more.
You should still b able to use aluminum plugs with the right anti-seize product. As for br*** plugs-do an online search "Using a br*** plug in an aluminum manifold is generally safe and acceptable, but it requires a proper thread sealant to prevent galvanic corrosion over time because br*** and aluminum are dissimilar metals on the galvanic scale. [ Material Compatibility & Corrosion Galvanic Potential: Br*** is relatively close to aluminum in the galvanic series compared to steel or stainless steel, meaning the risk of severe galvanic corrosion is low to moderate. [1, 2] Environment Matters: In dry or indoor compressed air/fluid setups, br*** and aluminum get along fine. In wet, salty, or high-moisture environments, direct metal-to-metal contact can still cause minor aluminum oxidation. Best Installation Practices Use a Sealant: Always apply a high-quality thread sealant—such as a PTFE thread tape or an anaerobic paste like Loc***e PST—to act as a physical barrier blocking moisture. Avoid Over-Tightening: Aluminum is soft and strips easily. Thread the br*** plug in carefully, and do not over-torque. And confirm,don't fully trust AI
If yur going for an early look, br*** plugs with raised square head, or flush with screw driver slot, look more righter. Hex socket plugs weren’t really a thing till later, maybe 50’s+(?)
Edmunds dual manifold for a Rocket? What's more "fifties" than that? The iron plugs that were in it were hex head, and they had been in there a looooong tine. I think I'm going with br*** hex head. The 1/2-20 (I checked with a thread chaser) had what looked to be an old oil pan drain plug (with washer) in it which also looked like it had been in there since the beginning. I think I'll use a socket head cap screw and sealant.
Strange I just ran into a repair needed on an L79 intake , this week .For some strange someone had drilled and taped 1/8 npt , hole in the heat crossover p***age . The owner wanted me to weld the hole shut . I explained to him , getting that exhaust p***age clean enough to get a nice weld would be tough with what we have to clean it with . So I rooted around in my junk and located an aluminum 1/8 in. , conduit plug , taped the hole deeper to allow the plug to tighten near flush . I coated up the threads with JB Weld tightened it up . When dry used a mini belt sander to sand it smooth and he had the the intake tumbled . It turned out really nice , if you would not have known there was a hole there you would not know it now .
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