Commanders,

I have a 68 35' Commander.  I need to replace the prop nut on my 1 3/8" driveshaft (stbd side).  By modern specs this should be a 1" prop nut.  However a standard 1" nut doesn't fit, it is too small.  It just spins over the end of the driveshaft and the threads won't engage.

I compared the size of my threads with a standard 1" bolt.  Mine are 1/32" larger.  

Any ideas?

Thanks,

Derrick

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I'm really confused ---- I was in the fastener business for 35 years and never heard of a 1&1/16 (1.062") tap, nor can I find one in McMaster Carr. My old mantra on McMaster was:  "If you can't find it in McMaster, it doesn't mean it doesn't exist, but you're gonna have a damn hard time finding it. "

So, where in the world did you find a tap size I've never heard of in 35 years. This "Bubba was here" saga is the weirdest screw-up I've ever heard of ----- ??

I see MSC has them listed in an H4 tolerance for $120.00. Really odd ball. This is engineered thread territory for truly specialized applications.

What we don't know is the major and minor thread depth on the shaft. I would guess that it is nonstandard implying that without verifying the actual thread profile there is a very good chance that even if you re-tap the nut for 1 1/16-8, it will not work.

One other side point, the nut will need to be bored to the minor thread diameter of the shaft for 1 1/16 thread size. Since the tap is an H4, the  design tolerance will be +-.002 on the thread diameters. With all of the guessing on this, I seriously doubt if this approach will be successful without a lot of hand work in fitting the nut to the shaft.

The whole problem with this approach is that it is backwards with how the shaft would be properly threaded. Normally, the machinist would have the nut in his hand. The shaft would then be threaded to match the nut. On this one we are trying to get a theoretical oddball standard nut which might also have been made by the original machinist to fit an unknown threaded shaft. Without knowing the minor and major diameters of the nut and the shaft, we don't know what we are aiming for. The H4 tap tolerance only complicates this.

If re-threading a 1-8 nut to make it a 1 1/16-8 nut is the chosen path, it is only going to compound supporting this in the future as the non-standard shaft threads will also require the non-standard nut. Even if two are made, both will need to be fitted to the shaft. I see a lot of work into making a kludge work. Sooner or later this will come back and bite you.

Re-working your shaft to the correct thread size is the best approach and likely the cheapest in the end. Tim's suggestion for the spare shaft is an excellent idea that will also probably save you from other problems in the future.



Dick Morland said:

I'm really confused ---- I was in the fastener business for 35 years and never heard of a 1&1/16 (1.062") tap, nor can I find one in McMaster Carr. My old mantra on McMaster was:  "If you can't find it in McMaster, it doesn't mean it doesn't exist, but you're gonna have a damn hard time finding it. "

So, where in the world did you find a tap size I've never heard of in 35 years. This "Bubba was here" saga is the weirdest screw-up I've ever heard of ----- ??

A friend talked me away from the ledge of the hack with the 1 1/16th.  Off to option 1.  It's the right solution.  I'll end up with a maintained driveshaft and the ability to service the cutlass bearing again with a standard nut if needed.

I'll consider the spare shaft.  Or alternatively making my current shaft the spare.

I like the split die thread chasers.  I'm going to get a set just for my general use.

The 1 1/6th is not an SAE size, it's a custom size some suppliers make.

Thanks everyone for your advice!

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