Adjustable Die For Crank Threads

[49hiawatha]

Suggestions ? What about an aluminum gas tank whose filling elevated cap opening has bunged up starter threads. About 1 1/8" internal dimension. Tried to chase it w/plastic type gas cap – NO go. Next used a metal threaded gas cap- No go. Only cutting oil on the metal threads. Any suggestion ? Threaded taps that size around? Thanks.

[chris-p]

Well I bought a thread file as suggested by Chris S, and it worked great. Cleaned them up, fixed the start of the thread, then ran a thread repair die down it and good as new!

[Mumbles]

quote 49Hiawatha:

About 1 1/8″ internal dimension. Threaded taps that size around?

It’s not a common size, 1 1/8 X 20, but taps are available.

Oltimer made his own thread repair tool for tanks by lathe cutting threads on a 1 1/8 shaft and then cutting a groove lengthwise to catch the chips.

https://www.amazon.com/1-1-8-20-TPI-THR … B00O2CX9DC

[oltimer]

quote Mumbles:

quote 49Hiawatha:

About 1 1/8″ internal dimension. Threaded taps that size around?

It’s not a common size, 1 1/8 X 20, but taps are available.

Oltimer made his own thread repair tool for tanks by lathe cutting threads on a 1 1/8 shaft and then cutting a groove lengthwise to catch the chips.

https://www.amazon.com/1-1-8-20-TPI-THR … B00O2CX9DC

Wow Jim, that’s a while ago, and I made it out of 245 high carbon steel on my lathe if others are interested in making one. Most Aluminum tank connections are made from 48/52, so I will never wear out my tap. I’ll post a pic up here in a couple of days for the usual visual connection. LOl

[green-thumbs]

I hacksawed and split a nut (7/16"x 20) then used vice grips as above. Had to go up thread
a number of times to get a "start" for die. Yes it does wear out the nut thread….a throw away
tool that served its purpose. Keep correct size nuts on hand to protect end of crankshaft
and propshaft. Ounce of prevention is worth a pound of cure.
Louis

I used a nut on hand . High grade nuts are available but maybe more difficult to saw and
split.

Mercury Service Tool Catalog lists two taps

1) for early tanks 1 1/8" x 18 N.S. (National Standard)
2) for later tanks with the ‘hex" filter in tank 1 3/16" x 16 N.S. (National Standard)
National Standard can be looked up in Machinist’s Handbook for specific detail to
make a tap to repair the threads.

There is a commentary on change from N.S. to U.N. that sums up change as refinement
of minor nature that affects gauge standards but the threads of both fasteners and threads
are fully mechanically interchangeable. Manufacturing allowances are great enough to
absorb refinements in gages.
Making a tap to restore thread in aluminum would not require hardening. Just a matter of turning 16 or 18 threads per inch on proper size bar stock and then cutting relief(s) lengthwise using milling machine. Simple if you know how and have the machines and
the tooling. Because it isn’t all that simple it might take several attempts to make a
tap that works. A situation where 30 or 40 years in the trade make it seem simple
until you try it. My late father in law was a very good old school machinist.

[Author]

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