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MG TD TF 1500 - Another what bolt question.

Fitting up the generator and I noted the bolt that holds the steel band on the back openings is a US thread bolt.

I searched all my nut/bolt references and did not find a listing for what is the correct original bolt for this.

I would assume it came from Lucas. Unsure what thread system Lucas used.

Bruce Cunha

1/4 26BSF pitch slotted round head

nut is square

I just had mine cad plated.

Frank

TF1414
Frank Cronin

Thanks for the fast response Frank. I will get it ordered.
Bruce Cunha

Did you know that the two screws holding the plate in the distributor are an old US thread originating from the early 20 century. The UK government realising that a motorised war was about to erupt (this was 1912) encouraged UK companies to go to the US and get manufacturing licences for magnetos from US makers. (Germany was dumping magnetos in the UK). Presumably Lucas got a licence and the threads were US.

Morris who had fitted Continental engines found that these particular engines was no longer going to be made bought the manufacturing rights. He subcontracted the manufacture to Hotchkiss in Coventry who had been making machine guns and being French used metric threads. They continued to use metric on the Bullnose engines; Morris bought them because they couldn't keep up with engine demand and the threads were not changed. Hence metrics in XPAG engines.
R J Marshall

I have to put up labels when I am working on the engine to remind me. I have been chasing the threads after painting and on occasion have grabbed the BSF tap instead of the Metric one.
Bruce Cunha

'Hence metrics in XPAG engines'. To complete the story the bolts had Whitworth heads so as to enable the British tool kits to be used on these engines. Apparently this weird marriage of fine metric threads and Whitworth heads gave rise to the term 'mad metric'. Cheers
Peter TD 5801
P Hehir


Might want to check that size. My generator has a 2BA X 1 1/4" length screw with square nut. I don't believe a 1/4 screw would go through the holes in my cover strap. (It is installed on my car so I didn't remove it to confirm details)
Richard Cameron

I have not wrapped my head around the BA threads yet. I still have to remember to convert the Whitworth to BSF when I order them.

How do you know if it is a BA? What is the thread pitch? I have pitch gauges for Whitworth, Metric, and US. Will these also give me the BA thread?

I know BA uses a number in front of it, but is there a conversion to use to tell me what size the screw would be if I measured its thickness?
Bruce Cunha


Web site: https://britishfasteners.com/threads/
Richard Cameron

Small diameter threads on these cars are always BA threads (can't think of any exceptions). The smallest BSF size is 3/16, and BA sizes larger than 2BA are rare (can't think of any on these cars either). However, 2BA and 3/16BSF are almost compatible over a short length - a bolt from one will fit a nut from the other, but not a threaded hole. Anything over 3/16BSF will be BSF (chassis) or Mad Metric (engine) withthe exception of the odd BSW or UNF fixing (later models).
Dave H
Dave Hill

I'm sorry got the numbers wrong Bruce! Major brain fart on my end. Now that I recall, I quoted what I just used recently when cleaning some hardware. Sorry!! Dave H is right on with his post. It took me a while to figure out the BA and BSF. If you select a 3/16 BSF 32 pitch tap or 2BA to chase a thread, both will work.





Frank Cronin

Frank, what is the purpose of the capacitor on the generator?

Thanks.

Jud
J. K. Chapin

Jud, I had one on an old Chevy I and it was for a radio noise suppressor. Without it, you could hear the generator wine through the radio. PJ
PJ Jennings

Got it. Thanks. Jud
J. K. Chapin

Comment on BA thread:

"but with diameters determined by a factor proportional to a power of the logarithm to the base 10 of the thread pitch in millimeters. ".

Now try translating that into English!

Peter
P G Gilvarry

This thread was discussed between 15/03/2019 and 17/03/2019

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