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MG TD TF 1500 - Numbers on the Generator Tach. Drive

I was cleaning the tach drive today. There is a brass plate riveted on it, the plate has P141 on the top and 2 25 1 on the bottom

The bottom looks like a date code. Is the top the gear ratio?

Bruce Cunha

The bottom is the gear ratio, 2.25:1, to be used when coupled with a dynamo pulley of 3-3/16" diameter.







David Padgett

If it were a uk date it would have been 25.2
C I Twidle

2,25 1 is the gear ratio.
Lew Palmer

Excellent. I thought I was going to have to look for an earlier tach drive to be correct for my Nov 1 1950 Car.

Thanks.


One other question on the tach drive. I appear to be missing the grease fitting. Does anyone know what the thread for this fitting is?



Bruce Cunha

You also have an original knurled cross hatched brass coupling nut! I have only seen 3 or 4 of those over the years. No clue about the thread. Take to parts store and try some zerks. I probably have one somewhere, let me know and I'll look. George
George Butz III

George, would the fitting have a British Pipe Thread instead of an NPT? If so, don't believe a FLAPS would have it.

https://www.ralstoninst.com/news/story/the-difference-between-npt-bspp-and-bspt-seals

https://www.valvesonline.com.au/references/threads/

Lonnie
TF7211
LM Cook

Another of those little details I will pass on to Chris to add to his web pages.

I did find the Greaser. Moss carries it.

Bruce Cunha

George:
Are you sure the original coupling nut was always cross knurled?
My ownership dates back to 1966.
My coupling nut was a much buggered up straight knurl.
It is possible that it was changed, since my engine is a replacement, but its so buggered I think its way before 66'

Jim B.
JA Benjamin

Don't think its a pipe thread as I fitted a grease nipple in mine a few months ago and found a suitable one in my spares box. Most likely to be BSF I think, but can check in the morning as its too late here now.
Dave H
Dave Hill

I forgot the picture.
Also it was aluminum.

Jim B.

Oh, I did make an exact duplicate.





JA Benjamin

Last month, when I installed the Dynamator, I found that the aluminum coupling nut on the repro tachometer drive wouldn't quite screw all the way on. I tried a send coupling nut, of the same type, and found the same effect. Fortunately, I had an old brass coupling nut that screwed right on, all the way. It's knurled, but not cross-knurled. Bud
Bud Krueger

I have a reproduction drive with the aluminum coupling nut. The Drive broke and I picked up this one at an MG swap meet.
Bruce Cunha

Jim, The new Smiths brand tach drives available in the early 70s had the same style aluminum nut as in your picture. I have a NOS knurled brass nut, and have seen the same on an original low mileage TD and a TF. I can't say for sure, but in my opinion that is what came from the factory. The current brass nuts with the linear lines came out some years ago. George
George Butz III

The thread on the grease nipple / zerk is 2BA or 3/16BSF - both fit.
Dave H
Dave Hill

According to the service parts catalog dated 1958 the original "Reduction box for revolution counter on dynamo" and its assorted parts never changed from chassis number TD0251.

Tim


Timothy Burchfield

OK Then.
George, at your convenience would you measure the width of the knurl, and the OD of the un-knurled section.
Looks like I need to make a brass one.

Jim B.
JA Benjamin

My presumed original parts contrasted with a new one.

J K Barter

Front to rear distance

George Butz III

Width of smooth part of collar

George Butz III

Knurled part width

George Butz III

ID of knurled end

George Butz III

Best close up of it with my phone, macro camera not available but could take a shot in a few days and post.

George Butz III

Thank you George;
Could you give me one more?
Width of knurled ring section.


Jim B.
JA Benjamin

Jim, Yes, but it will be the end of the week. George
George Butz III

Total width 0.883, wall width knurled part from outer to inner ID: 0.134"
George Butz III

Thank you George.
Jim B.
JA Benjamin

I wanted to see if my existing diamond Knurls were acceptable.

I had a short piece of 1" brass, not enough for a full nut.
(1 foot is on order)

The knurling still needs adjustment, since one knurl is not fully engaged.

Given that, is the pitch of the Knurl acceptable?

Georges original on top.
My dummy on the bottom.

Jim B.

JA Benjamin

I finished chassing the thread today.
Its 3/4-26 BSF.

Because I changed out the leaking speedo drive I had a test piece, with the same thread to fit the nut to.

Close enough now.

Jim B.

JA Benjamin

I finished chasing the thread today.
Its 3/4-26 BSF.

Because I changed out the leaking speedo drive I had a test piece, with the same thread to fit the nut to.

Close enough now.

Jim B.

JA Benjamin

The thread is British Standard Brass (BSB) 26 tpi 55 deg, British Standard Cycle (BSC) is similar at 26 tpi 60 deg.
Both are 26 tpi at all diameters.
Ray TF 2884
Ray Lee

Nice work!
George Butz III

Yes Ray.
I used a 55 degree tool.

Jim B
JA Benjamin

This thread was discussed between 21/03/2019 and 15/04/2019

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