Loose Carburetor to Manifold studs

[lyle11]

I have reviewed past topics on worn carburetor threads for the manifold studs. I realize I can drill them out and use a bolt and nut or Heli-Coil them. The threads in my carburetor for the manifold studs look worn and feel loose, but based on running a cleanup tap down them it feels like they have a couple good solid threads at the bottom of the hole. The cleanup tap bottoms and feels snug. But, I m thinking it isn’t gonna hold up under vibration with only a couple good threads.

So, I figured I had a couple of options and wanted your opinions.

Option 1 - Use threadlocker on the studs. Any reason why this wouldn’t work?

Option 2 - Run a 1/4-20 tap all the way through. Use a longer stud and add a nut to the protruding threads.

Thanks

[staninlowerAL]

I prefer option 2, run the stud up from the bottom and use a self locking nut. Someone is going to need to remove it one day

[inairam]

I would use a threaded insert the correct studs and not use nuts on the bottom

[Stanton]

I have two Cubs, both with the IH 3/4 updraft carb. Both carbs have manifold bolt holes that go all the way through the carb-to-manifold flange. I thought that's the way all the 3/4 updraft carbs were.

Are you saying that those stud holes bottomed out on original carbs--studs don't go all the way through?

Regardless, think I'd drill them out and use Helicoil inserts. They'd last forever.

[Don McCombs]

Holes go all the way through. The proper repair, for durability, is to helicoil the holes. Several forum members are set up to do this repair. Perhaps one of them will contact you by PM.

[inairam]

As Don wrote the holes go through but there is no bolt on the bottom.

see photo http://www.tmtractor.com/tm-tractor/gfl ... or_001.htm

[lyle11]

The holes go all the way through, but, on one side the cleanup tap stops when it protrudes about 1/32 of an inch. That’s what I meant by “bottoming”, not a blind hole. I didn’t force it through in the soft metal. I’m just running the tap in with my fingers, so it might just be hung up an imperfection in the threads.

I haven’t taken the carburetor apart yet to determine if it is warped or has other reasons I might want to pay someone with carburetor expertise to add the Heli-Coils, etc.

Once I take it apart, if I decide to have someone else work on it, I’ll put something in the Vine. I actually have another IH carb with this same issue. Maybe I could do a 2 for 1 swap for getting one of them fixed right. The tractor will run with either carburetor bolted on.

Thanks for your replies.

[Gary Dotson]

Since you have two carbs with thread issues, you should pick up a 1/4 X 20 helicoil kit and repair both of them. It is not at all difficult to do and you'll have the kit going forward.

[lyle11]

That is what I have been looking at. Trying to get educated on Heli-coils. Looks like you can get a 1/4-20 kit with the drill bit and tap online for about $20 shipped. Not sure if any local place sells them. It led to a couple of questions:

1.) One carb top has real good fuel inlet threads so that is my preferred one to use. However, one carburetor manifold stud hole was drilled out to 5/16”. So, based on the chart I looked at, assuming I am understanding it correctly, the drill for a 1/4-20 helicoil drills a 6.7 MM hole or .26” but 5/16”=.31”
Is the hole already too large for the 1/4-20 helicoil kit?

2.) On the other carburetor top I am sure the manifold stud holes can be fixed with a 1/4-20 helicoil. But, the fuel inlet looks to have been cross threaded. I briefly looked at a “How To” about fixing it with JB Weld but I’m not sure in want to go that route. Maybe add an additional fitting with threadlocker. A good fitting fuel inlet is more important to me than the manifold studs.

I have not yet separated the carburetors. The one with the bad fuel inlet is a lot more beat up on the outside like it was tapped on a lot but I haven’t checked inside.

Would be interested in an answer to question #1 and any comments or suggestions for fixing the fuel inlet.

Thanks

[staninlowerAL]

I can't answer question #1. Question #2, the fuel inlet threads can be helicoiled back to OEM size (1/2 x 20 bolt threads) with the correct tools to align and install the helicoil. Other possibilities are retap the hole for the fuel inlet fitting to pipe thread, JB Weld a fitting in place, or use a 5/16 tubing union and rethread one side of it to 1/2 x 20 to screw into the carb fuel inlet. Lacking the tools to do a helicoil, I prefer the last option listed.

[Stanton]

Comments/Replies:

1) I've heard of people installing a double Helicoil, larger then smaller, so the finished size would be the desired size, but then you're buying two kits. You might use a jam nut (thinner than an ordinary nut) and extend the stud down to just get the jam nut fully threaded.

2) One of my carbs was cross-threaded or stripped out. I used the JB Weld method and it worked fine, for a while. Finally used a Helicoil and haven't regretted it. Now, I can tighten the fuel line connection and not worry about stripping the threads out. Stan's suggestion (above; as I was writing this) is a good one too, then you can use one wrench the stabilize the fixed JB Welded fitting while turning the insert with another wrench.

These old pot-metal carbs need some TLC after 60+ years. Hope this helps.

[Bob McCarty]

The hole is probably borderline for a helicoil. There are also solid inserts like EZ-lok that will fix a larger hole and use a standard size drill bit and tap. The gas inlet can be helicoiled, but is tricky to do without a pilot jig that Rick Prentice first made. I occasionally use an Edelmann 16840 fitting. If the inlet is too stripped for a helicoil, I JB Weld the threaded part in. You have to cut off the existing ferrule and shorten the gas line a little to adjust for the length of the fitting.

[lyle11]

I was able to determine by looking at the specs for the 1/4-20 helicoil kit, that the drill size is significantly smaller than 5/16” and helicoil is not an option on that side. The 1/4-20 EZ-Loc requires a 23/64” drill. That might be an option, but the drilled out side is the one close to the idle screw, and at 5/16” is already almost up to the carburetor body before drilling out another 3/64”.

Anyway, thanks for the comments and ideas. I might do and EZ-Loc on one side and just bolt the other one with a nut filed on one side. I was wondering if there might be some type of threaded insert with a flange that could be inserted from the bottom and locked into place with threadlocker. I’ll figure something out.

Thanks

[Nelson 634]

There use to be a product that worked similar to a pop rivet only it had a thread in it. You screwed the stem out instead of it breaking off. I think it was called a thread-sert. I used them all the time during my time as a maintenance supervisor in a textile mill. They worked well set into aluminum plates we used to mount circuit boards onto. I'll look to see if I can find any further info. and I may have one lying around.

[Nelson 634]

I got the name wrong they are called nut-serts. Grainger has something very similar called a nut insert. They are a bit pricey as you have to buy 50 pieces @ .74 X 50 = $37.00 Amazon has something called Stainless Steel Rivet Nuts Flat Head Insert Nutsert 1/4-20UNC. 20 ea. under ten dollars.