1964 S type

[Glyn Ruck]

Pleased you got it out!

[JCS]

“Perhaps someone can enlighten me as to what a 2BA stud is and my day will deemed fruitful”

O.K ……RollyTG………..

There seems to be some confusion regarding what I suggested for replacement studs on the Otter switch and also the general threading arrangements.

I was suggesting using both 2 BA brass nuts and studs and no steel, and the tap if supplied was to be a 2 BA taper tap merely to clean up the original threads.

The existing three set screws are almost certain to be 2BA. That falls in with the early 1950’s British motor manufactures convention on thread sizes, on the changeover from BSF to UNF. This encourages owners, and sometimes specialists to assume the smaller sizes are also UN/Unified.

Both before and after this change, studs, bolts and set screws under ¼ inch used BA threads, usually from 0 BA to 6 BA.

The exception to the BA below ¼ inch rule was that American Standard threads were used on ignition distributors and some other products made by Delco Remy and a few carburettors had the odd American Standard screws. These exceptions occurred on American designed products even before “standardisation” to Unified.

The BA (British Association) threads are similar to Whitworth in that the root and crest of the thread are rounded, the thread angle being only 47.5 degrees. The rounded root helps prevent, very usefully, tearing up in the thread. The 2BA is the most popular of the BA threads with 31.4 threads per inch, requiring a tapping drill size of 4.00 mm and clearance drilling of 4.80 mm. Unfortunately, one of the American Standard sizes is very close to 2BA and rips out the bottom of the threads.
The BA threads originated in the Swiss watch industry where they became a standard for watches. Only used in the USA for export tools, but used fairly wide in Europe and in the Electrical industry in England. Used quite extensively on top end cars particularly in fuse boxes and anchors for steering column shroud nuts and screws. Rolls-Royce and Bentley cars are full of them, including otter switches!

[Norton]

Imperial bolts and threads is complicated, confusing and some consider it to be fun..
I will not claim to have deep knowledge of imperial threads and bolts!
But the two bolts I removed that did not break, I measured to be 3/16 ( 0.1875 inch ) whitch is close enough to be 2BA ( 0.1850 inch ). Measured thread to be 24 tpi whitch is definitely not BA. And head 5/16 AF. 2BA have, to my knowledge 31.4 tpi. The one I drilled out I cleaned up with a 3/16 24tpi withworth tap. Did not have a suitable bolt so I made a new, actually «converted» a 5mm bolt. Grinded it down and cut new threads with a 3/16 withworth die. That worked fine, but did not try old bolts in cleaned up hole or vice verca. My car may of course have been modified in this area without my knowledge.

Harald.

[JCS]

Harald

Your car seems to be standard, and you are correct the set screws are NOT 2 BA.

Since reading your experience I investigated the sizes further.

The set screws are officially listed as No.10 Coarse Thread Series 5/8 th UNC 24 TPI.

Thank you for the information.

Norman

[Norton]

Update:
My new otter switch also cut the AED out a bit on the early side. But not as much as the one I removed, and adjusted with the hit and miss method by using a hotgun.
Now the bolts are easily enough removed so I decided to test the old adjusted otter switch in practice. And in my opinion it suits the engine temperatures much better.

As I cleaned up the seized bolt hole with a withworth tap and made a new withworth bolt, I better not mix it with the two others. They are as Norman states, 5/8 th UNC 24 TPI. They are a a bit different with regard to thread angle. On the other side its mot a very stressed installation but not good practice to mix them.

Rgds Harald

[MortonChurch]

Windscreen wiper motor



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