1929 Plymouth distributor shaft

[seasand]

I have had my 1929 Plymouth engine rebuilt. It really ran great for the first 100 miles then the shaft that turns the distributor sheared off. The tab at the bottom that engages the gear coming out of the engine. I had a machinist make another one and replaced it. The world was great again until yesterday when after putting about 75 miles on the car the shaft sheared again. Has anyone had a similar problem? Any suggestions?
George

[Crazydave]

I have sheared one off, but was using a homemade garage engineered base. It happened when I cranked both bolts in tight, not a perfect fit apparently.

What comes to mind for you to check is the tab. It is offset. If installed wrong, I would assume it would fail but had a spare (wrong drive, same shaft) that was bent like it was installed wrong.

The other thing I did when attempting to straighten a bend tab was only put one bolt in the base. Then observe the wobble for troubleshooting, instead of bolting down hard potentially twisting it off. I straighten the bend one and use still use it today.

I have pictures for reference, showing the offset. If you already know this, I would check alignments.