Carb Thread Repair

[ferricsteed]

I managed to strip the internal threads of H2 carb, body 3578, where the bottom bolt securing the float bowl screws in. What is the thread size? My best guess is 7/16"
18 tpi Bsp. Is a helicoil thread insert the best solution? Is a helicoil insert even made for pipe thread? I imagine straight thread pattern could be made to work but before I bugger up this carb body even more, advice would be greatly appreciated.
On a similar note, how best to seal fuel leaks at this joint? SU drawings show 3 washers below the float bowl, middle washer made of brass. Multiple washers seem destined to leak. Replace with one fiber washer? Possibly use one of those A/C (air conditioning) washers with o-ring material sandwiched on both sides of washer?
Tim Bloomfield
TB0613

[Steve Simmons]

The thread is 7/16-18 BSF as I recall. I know repair kits are out there. Joe Curto and Butch Taras both offer repair services.

[Duncan M]

Why introduce a "rubber" part to a system that is designed to be leak free without it? "Rubber" will dry up and be useless at some point in time. Also, that joint you are talking about is intended to be moveable or slightly adjustable. 5 years from now when you are re-adjusting the float bowl level and fine tuning the fuel height in jet--you may want to re-negotiate the float bowl orientation slightly, and an O-ring or Dowty washer will tear or distort and cause leaks unless you take it all apart and install new.

[ferricsteed]

Good point Duncan. I'll nix the dowty washer.
You state it is designed to be moveable; interesting concept. I would adjust float level by the forks, and/or washers if using grose style needle and seat. I do know some try rotating the float chamber to prevent overheating. This rotation may change the fuel level in the jet. I am focused only on reducing/eliminating fuel leaks at this joint. I haven't heard anyone recommending a sealant.....yet.
Thanks,
Tim

[ferricsteed]

Thank you Steve. I have reached out to Joe and Doug. I'll hear from them after the holidays. I have used Butch too. All three are craftsmen.
I am thinking I can handle this repair. You gave me confirmation on thread size. I ordered a 7/16-18 bsf helicoil (EZLoc). Not a common size. I'll deal with it being straight versus tapered pipe thread.
Tim

[Duncan M]

You could always do a light dressing of the fiber washers with Hylomar blue. Permatex 95420 is the permatex version of the (non-silicone) Hylomar blue.

[Rob Reilly]

<I'll deal with it being straight versus tapered pipe thread.>

It should be a straight thread.

Moss shows a single large fiber washer above.

and 3 washers below, one brass or steel and two fiber.