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MG TD TF 1500 - Generator shaft nut

Hi
Yesterday there was a new rattle noise from the front engine compartment on the TF. After some investigation with my stethoscope, I narrowed it to the front of the generator. Drat! I thought. Perished bearing.
I just pulled the generator out and the pulley assembly fell right off. The NUT was gone. Bearing feels fine.
Has this happened to anyone else?
Can't find the nut. Does anyone out there know the size of the nut? Better yet, does anyone have one to spare they would mail me?

Tom
'54 TF
T Norby

Tom - e-mail me at SUfuelpumps@donobi.net, I may have a spare nut. Cheers - Dave
DW DuBois

And when reinstalling don't forget a large lock washer and maybe some Locktite.
John Quilter

Or even a Nylock lock nut once the thread type is identified. Cheers
Peter TD 5801
P Hehir

Locking tab washer I think was used during that time.
G Evans

I found a metric nylock nut locally. It fit perfectly. I'm back in business.

Thanks

Tom
'54 TF
T Norby

I had this happen years ago. The loose pulley caused the key to damage the keyway slot in the pulley. I recommend you inspect the pulley before re-assembly. Regards, John
JR Mahone

Just a note to share my experience. I had to take the generator out to replace the pulley nut. Ran it tonight and the red gen light would not go out. After a few minutes of concentration I recalled that I may need to re-polarize the generator. Went and reviewed the John Twist utube video and did it. I was surprised that I needed to spark the A and E regulator contacts several times to get the gen light to go out. Like 10 times.
Finally got it running well.

Tom
'54 TF
T Norby

I just stripped the nut. Can anyone tell me what the thread is? I'm guessing that it's 12-1.5. Naturally, the local hardware places only carry the course version, 12-1.75.

Tom Norby, where did get the nylock? Tnx, Bud
Bud Krueger

Bud
Threads for the South --are showing them and have
12 x 1.25/1.5/1.75

I don't know which pitch it is but you could take the gen. in with you and get it matched up

https://www.threadsforthesouth.com/m12-15-nylon-insert-locknut-din985-cl8-zinc-prod-3174.html

willy

35ft/lb for the nut in my book--
William Revit

Thanks, Willy. I've gauged it to be 1.5. I just want to get concurrence. 1.75 nuts are on the shelf at Home Depot. 1.25 is very rare. I'll probably be ordering one via email or phone.
I'd love to find a nyloc. Have to find that Threads For The South location. I'm in Marietta. Thanks, again. Bud
Bud Krueger

Hey Bud
There's a contact us button up top rh side on that page I posted--

and-
Threads for the South, Inc - HQ / Marietta
1076 King Industrial Drive
Marietta, GA 30062
770-425-3787
Fax: 770-421-0637

Cheers
willy


If you have a Toyota dealer nearby ,they might be worth a try---Toyotas tend to use the finer thread a lot
William Revit

Tom,

To answer your question:

The thread of the nut is 7/16" BSF 18TPI. I would not use any "near enough" thread.
Original Lucas part number is: 180740


John


J Scragg

Bud,

I should have addressed my response to you, I didn't notice that you pulled the thread from the archives.

John
J Scragg

Willy, Thanks for that info and link to their site! PJ
PJ Jennings

Abingdon Spares have the nut $0.35, just got one the other week. Got the spacer, key, washer and nut.

Anybody have a spare later pulley for TD/TF? I am building a spare generator.

Thanks,

Peter

P G Gilvarry

See http://www.ttalk.info/DynamoNut.htm for the latest. I suspect that the thread of the nut for the generator is the 7/16" BSF 18TPI, not the M12-1.5 thread. It appears that the Dynamator shaft thread is metric, not BSF. But, the metric thread will fit onto the dynamo. And then it strips when you go to torque it up. Bud
Bud Krueger

Good work Bud---
very tricky of them to have the similar but not quite the same threads on the two units--A bit of a trap waiting to catch us out there
Glad you got it sorted
Sorry I wasn't much help there all up
John's product knowledge has saved the day
Cheers
willy
William Revit

Bud,

I have read your report on how you tried to identify these threads, you did a good job, however, for the sake of completeness May I add some comments.
You concentrated on two parameters:
1/ the crest diameter (outside) diameter.
2/ the pitch, = 1/TPI.

The problem is there is a third critical parameter, the thread PROFILE. The profile is defined in the spec of the thread standard, these standards are:

1/ Imperial (BS).
2/ American (UN).
3/ Metric (M)

Each standard specifies a lot parameters, but there are Three critical ones:
1/ the crest diameter (outside) diameter.
2/ the pitch, = 1/TPI.
3/ The thread angle.

Imperial use an angle of 55° (but not always)
American use 60°
Metric use 60°

From simple geometry it is easy to see that if you ignore this you will be (excuse the feeble pun) screwed.

It is one reason that, as a rule NEVER interchange thread types.

John






J Scragg

A BIG WHOOOPS!! Last night I went to Abingdon Spares' website to order a nut. There, in front of my eyes, was their identifier for the TD/TF nut, 7/16 20TPI, not 7/16 18TPI. Careful work with the thread gauge confirmed the shaft thread.
This morning I went to Threads for the South, Inc.( a very short trip from my home)and bought a couple of 7/16-20 Gr.8 Nuts and 7/16-20 Nylon Insert GR 8 Nuts and a 7/16-20 Die. Sure enough, the 7/16-20 die cleaned up the shaft. Found that the Grade 8 Nyloc nut goes on far enough for the shaft to go completely through the nylon. I prefer that to a nut/lock washer combo that leaves nut threads showing.

So, John, I'm not mixing metric with anything, but I could be mixing American and Imperial. I'll live with it. Thanks for your sleuthing, willy.
Now to go and rewrite the DynamoNut webpage. Bud
Bud Krueger

Bud , I'd guess that Threads from the South are your new best friend----glad you got it sorted.

willy

Just some useless info I came accross
The generator shaft was probably Brittish Standard Cycle-course thread
BSC thread is usually 26tpi but as the thread diameter gets into larger sizes there was a 20tpi option
This is the most likely option as UNF wouldn't have been common then ,it would have been the old Brittish threads or SAE

Unified threads(UNF-UNC) were introduced in Nov 1949(for 1950) but earlier threads like Whitworth and SAE still continued and still do and would have been a carryover on production lines until there was the need for a model change or something
In MG's case that would probably have been MGA time I'm guessing

Both 7/16 UNF and 7/16 BSC-course are 20tpi and both 60degree threads but there might have been a very slight difference in thread form, but insignificant----As you have run a UNF(i suspect) die over the shaft to clean the thread up ,it is now UNF for sure and your new UNF nuts should be spot on
From what I've read the two threads are almost identical and there isn't an issue interchanging except for the odd rare case that a unf bolt 'might' be a tiddle fat for a BSC course nut and the nut might need a tap running through it but rare

END of useless info, but interesting though I thought
Cheers
William Revit

This thread was discussed between 07/08/2016 and 29/11/2021

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