Aluminum Head Thread Repair

Shoebox

Shoebox

Well-known member
I have a pair of pretty decent 8ba Edmunds heads that I would like to use after some work. The thermostat housing bolt holes were apparently stripped at some point and the bolt holes on both heads to varying degrees were grossly drilled out and re-tapped. I believe they're beyond thread inserts like Time Certs, and should probably be welded up, drilled and re-tapped. Before I go down this rabbit hole I wanted to bring this up on the Barn. Thank Youl
 

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Shoebox said:
I have a pair of pretty decent 8ba Edmunds heads that I would like to use after some work. The thermostat housing bolt holes were apparently stripped at some point and the bolt holes on both heads to varying degrees were grossly drilled out and re-tapped. I believe they're beyond thread inserts like Time Certs, and should probably be welded up, drilled and re-tapped. Before I go down this rabbit hole I wanted to bring this up on the Barn. Thank Youl
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571971
 
I have fixed Stromburg inlets by making my own inserts. Your heads could use the same idea. I selected a bolt and drilled and taped it to the size needed. I partially tapped the part so the insert could not screw thru. Thread locker so it would not screw out You would have a permanent fix and no welding.
 
Andy said:
I have fixed Stromburg inlets by making my own inserts. Your heads could use the same idea. I selected a bolt and drilled and taped it to the size needed. I partially tapped the part so the insert could not screw thru. Thread locker so it would not screw out You would have a permanent fix and no welding.
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I like this idea. There are also stepped studs. The insert side is usually one size larger than the nut/needed thread, but there could be ones with two.
 
I have found, its all in the person doing the welding......There are welders who work at a welding shop and has years of OJT and welding....BUT its not the same as an AWS "certified" welder ie one who's really knows his stuff!!!!! Fortunately I have access to one or more of them as my customers
 
I really appreciate the recommendations and comments, I'm not in a real rush to affect repairs on these heads so I'm looking into ALL suggestions made so far. I do know an awesome certified welder, however as Tubman mentioned, welding on old aluminum could be a crap shoot. I will throw this out... how about packing the bolt cavities with Aluminum JB weld followed by drilling and tapping?
 
I did this on a 49er on one side tapped it out to the next size ,locked tight stud with a nut ,cast iron head worked great .
 
Shoebox said:
I really appreciate the recommendations and comments, I'm not in a real rush to affect repairs on these heads so I'm looking into ALL suggestions made so far. I do know an awesome certified welder, however as Tubman mentioned, welding on old aluminum could be a crap shoot. I will throw this out... how about packing the bolt cavities with Aluminum JB weld followed by drilling and tapping?
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I had a stripped thread in one of the thermostat housing mounting holes in the aluminum intake manifold in my Corvette when I got it in 1987. I repaired it then with Loctite's Thread Repair kit. Fast forward to 2020. I had to replace the valve guide seals in the same car. When I pulled it apart, I remembered the repair I had done 33 years before. I had completely forgotten about it, but it still looked good. I highly recommend the stuff. There may be better alternative products available these days. Tremendous strides have been made in this area in the last few years.
 
They also make double ended studs with different sizes on each end. You can drill and tap to the next size up and get the corresponding stud to insert. Lock-tight the stud in the head and use a nut on the outside of the thermostat housing.
 
The real challenge here is that the holes have been hogged out WAY beyond the next size up. It looked like the solution was to use Big Serts as Tubman suggested, designed for situations where a previous attempt to repair had failed. I contacted Time-Sert and asked what was the drill size included in the kit, and the holes in the heads are that large or slightly larger. At this point I'm favoring the JB Weld or actual welding up of the holes. I do have a very skilled certified welder friend who has seen what I have and felt it was very doable. I'm not in a rush here and will continue to consider which way to go. Continued comments most welcome. Thanks.
 
Where it me, I have modified some carburetor adapters. What I did was drill and tap the whole to the next biggest size, which for me was 3/8-16, then I cut the head off the aluminum bolt (I sell them) and threaded part of it into my hole about 1/2 up from the bottom, then my welder welded the other half with weld and fill weld...THEN he was able to get to the back side and we burred out a V in the back side and he welded that. I then milled both surfaces back flat and re-drilled and tapped the correct 5/16-18 thread I needed!!! IF it is welded proper, you can't beat it from original!!!!


You can get a couple aluminum bolts at McMaster Carr IF need be, OR depending on the size??? I may have them
 
I opted to turn repairs for the thermostat housings over to a professional machine shop. Several spark plug holes were loose so they made aluminum bushings which threaded in and then were pinned. I believe next I'll glass bead the heads to clean up a bit.
 

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Looks great, good decision.....I think you're gonna have plenty of years of peace of mind driving and not wondering and money's well spent
 
Shoebox said:
I opted to turn repairs for the thermostat housings over to a professional machine shop. Several spark plug holes were loose so they made aluminum bushings which threaded in and then were pinned. I believe next I'll glass bead the heads to clean up a bit.
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