Thread form on engine mounting studs

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Thread form on engine mounting studs

Postby harry wilkinson » 12 Dec 2010, 00:05

This is my first attempt to use the forum, If I mess up I apologize in advance. I have several questions of a general nature, but I will start with just one first and see how it goes. The main engine bolts on my 47 engined Scott are 5/8 - 20 and the thread profile, as measured on an Optical Comparitor, is 55 degrees. 5/8-BSF has a 55 degree profile but not 20 TPI and a Cycle thread is 60 degrees. Is there anyone who can tell me what profile is correct. :!:
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Postby dave bushell » 12 Dec 2010, 10:59

Hi Harry
Your posting is under the wrong heading. It should be posted under "General Scott Topics".
I think your thread form should be 20 tpi cycle, but if you post again under the right heading, you will probably get a more definite answer.
Dave
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Postby efr215 » 12 Dec 2010, 14:04

Many manufacturers were/are very fond of “doing their own thing” when it comes to both thread diameters and pitches, in fairness on occasions there were probably very good design reasons but I sometimes suspect it was merely a bloody minded attempt to force people to buy their spares! There are more prosaic reasons too; maybe they already had the tooling for that particular thread form or the machine used for manufacturing was easier to set up for that particular pitch.

The fact is that the 20tpi Whitworth form was a quite popular pitch when something finer than the standard BSF was required, I doubt there is anything in its choice more sinister than convenience. Certainly it is a little more robust than the finer cycle thread in a mucky environment and the cycle thread was never very widely used.
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Stud thread profile

Postby harry wilkinson » 12 Dec 2010, 22:19

Thanks for your help I will post in the correct section
harry wilkinson
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Joined: 16 Jul 2010, 02:38
Location: New Jersey, USA


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