Scew thread size & type?

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Keith.owen
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Scew thread size & type?

Postby Keith.owen » Mon Apr 01, 2019 9:38 am

Hi,
Does anyone know what the thread type and size are for the screw that holds the Bakelite end plate with the F & D terminals to the casting / dynamo body?

I want to purchase a long screw and some nuts so that I can get a direct earth connection to the dynamo.

Thanks,
Keith
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Re: Scew thread size & type?

Postby pete.collings » Mon Apr 01, 2019 11:06 am

It's 2BA, commonly available. I can supply a length of 2BA studding (cut from a longer bolt) plus a couple of nuts, for the cost of a stamp.

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Re: Scew thread size & type?

Postby Bob.Murphy » Mon Apr 01, 2019 11:23 am

Keith,

Mine is on the bench at the moment so I measured it . . Its small!

Thread appears to be 40 tpi (my thread gauge is not very precise at this end of the scale).

Thread diameter = 3.50mm / 0.1375 inch

Total length of bolt shank = 14.58mm / 0.574 inch.

Thread length = 7.27mm / 0.286 inch.

Plain shank length = 7.26mm / 0.286 inch.

Plain shank diameter = 2.74mm / 0.107 inch.

Hex head diameter = 6.32mm / 0.2485 inch.

I thought it was BA 4 - but it isn't !

1/8" Whitworth is 40 tpi, but 1/8" = 0.125" - not 0.1375" !

It looks like a "Special" . . . .

Time to get the lathe fired up ;) .

Bob.
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Re: Scew thread size & type?

Postby Bob.Murphy » Mon Apr 01, 2019 11:31 am

pete.collings wrote:It's 2BA, commonly available. I can supply a length of 2BA studding (cut from a longer bolt) plus a couple of nuts, for the cost of a stamp.


Errrm . . 2BA is 0.1850 inch over the thread, this bolt of mine is definitely 0.1375 inch.

I tried my bolt in a 3BA fitting - its smaller than 3BA but larger than 4BA (I tried it in a 4BA die).

Did they change the dynamo fittings at some time ??

I have a feeling that this thread will grow like Topsy !

Bob.
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Re: Scew thread size & type?

Postby Mick D » Mon Apr 01, 2019 1:35 pm

Hi
I think it's probably 6-40 UNF, (and probably not original).
Regards Mick

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Re: Scew thread size & type?

Postby pete.collings » Mon Apr 01, 2019 11:09 pm

Perhaps it is a reflection on the state of many threads I have encountered in this area that a 2BA screw will invariably fit, even if it was originally a smaller, finer thread. I will take a closer look at the best condition end I have, to see if I can ascertain exactly what the thread size is, but would suggest that a 2BA screw is undoubtably easier to find, and with a suitable lockwashe,r or fibre washer and a dab of low strength loctite, it is unlikely to come loose.

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Re: Scew thread size & type?

Postby pete.collings » Tue Apr 02, 2019 4:50 pm

I have now looked at two dynamo ends, believed to be NOS, and both have a 2BA thread to retain the end cap.
They are the latest type of end, for use with the one piece metal end cover, so whether the thread was changed to suit the more robust endcap design,I do not know, although looking at a used earlier type of end, that appears to also be 2BA (but may have been converted).
So, take your choice.
The brush plate retaining screws are 6BA, and I believe Lucas used a 3BA thread on magneto points block/armature screws, so I would have thought Lucas standardised on BA threads, although one never knows with Lucas :? :?

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Re: Scew thread size & type?

Postby pete.collings » Sun Apr 07, 2019 12:41 pm

Keith
I had PM'd you, but message has not been picked up yet.

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Re: Scew thread size & type?

Postby Keith.owen » Mon Apr 08, 2019 9:24 am

All,
I have resolved my problem with the voltage regulator not switching on.

Despite having measured the resistance between the dynamo body and the earthing point below the saddle, and it having appeared to be fine, it was not since connecting a wire directly between said earthing point and the dynamo body, using the screw that holds the end cover in place, seams to have cured the problem.

So, I think that should anyone out there ever have a similar problem, this is possibly a simple fix.

I am pleased to say the least. It now just remains to make a tidy modification. :mrgreen:

Keith
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