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MG Midget and Sprite Technical - Fulcrum pin thread

Does anyone know for sure what the thread specification of the wishbone / kingpin fulcrum pin is other than being 16 tpi.
Alan Anstead

Alan,

I don't know for sure but it always seemed to me that the small end was 9/16" BSF with the larger end being custom. From the archives back in 23/12/2005 "To answer your original question, the threads appear to be 9/16" x 16 tpi for the small end, and 21/32" x 16 tpi for the large end" the thread was titled "Fulcrum pin tap size?". All the good quality fulcrum pins I have had used a bright ground finish and the profile seemed to match BSF/BSW with a well defined root and crest radius. IIRC this came up last year in a thread and one of the contributors said they had the facilities available to measure the profile accurately and give a definitive answer but I can't remember if the result was posted. It would be good to know. I presume this information isn't available from the BMC/Austin archives hence the question.
David Billington

David

You may be confusing it with the thread entitled 'valve rocker adjuster' from November 2016.

I will see if I can get one measured next time I'm in the office.
Dave O'Neill 2

Dave,

Maybe you're correct, my memory is good but not perfect, and I think having found the thread you refer too you are correct and that is what I was thinking of. Any possibility you can work the magic and measure a fulcrum pin?
David Billington

After the popularity of my clutch release bearings i was wondering if I could make / have made some wishbone repair kits.
The A30/35 OC supply them to their members.
I would also have to find out what grade of steel is used.
No more than a day dream at present but any info would help.
Alan



Alan Anstead

I was always under the impression that it wasn't a conventional thread, but a "special" which is in effect a flat bearing surface concertinerd up into a shorter space. The threads on the fulcrum pins look odd to me - too pointy. But then I am not an engineer!

I do know that 25 years ago the wishbone bushes were readily available for a few pence from several of the suppliers. I bought a couple of pairs but chickened out on installing them because I wasn't confident in being able to braise well enough on such a critical component. When this topic was raised a little while ago I went looking for them but couldn't find where I have hidden them.

If the A30/35 club supply them to their members, maybe some inter-club arrangement could be made between MASC and them. Or at least get the technical details from them.
GuyW

I still have a few wishbones left, if anyone wants to try it.
Dave O'Neill 2

Dave
If you are going to the Practical Classics Show NEC I wouldn't mind a couple of wish-bones to play with. I will be 'front of house' on the Masc Stand (Hall 5 Stand 540) on all days.

Guy.
Tried that with A35 OC but can try again. Might have to tempt them with clutch release bearings!

Alan
Alan Anstead

Alan,
As the Sprite is sometimes referred to as a convertable, 2 seater A30 I find it hard to believe the A35 OC wouldn't want to cooperate. I don't see any good reason why not, but then some can be funny about this sort of thing!

Can you advise Jan on his T9 installation on the other thread? (1275 release bearing movement) You have done many more of these than I (and I never claimed to be a "pioneer"! ). I now have a concentric slave/ release bearing arraangement, and when I originally installed my T9 one had to cut the guide tube off completely, which in turn gave rise to other problems.
GuyW

You would have thought that they would be happy to supply the wider community that uses these wishbones or at least provide the details about who makes them so others can get batches made.

http://www.austina30a35ownersclub.co.uk/ClubSpares.aspx?SparesCatID=7

I guess the information is out there somewhere as the threaded trunnions are made and not expensive at around £10 new.
David Billington

Alan

I'm not planning to go to the NEC, but I'm only a 10 minute drive away, so you could pick some up, if you wanted.
Dave O'Neill 2

Dave
Sounds like a plan.
alan dot anstead at btopenworld.com
if you can let me have an address and contact number.
Alan
Alan Anstead

I have the tap to properly thread the bushings. It is in a case that may have the thread sizes on it, I will look tonight and post any info on it.
J Bubela

J Bubela,

Is that the special tap which taps both bushes at the same time? I have been told they exist but have never seen one or seen mention of them elsewhere so a rare beast if so. Would be great if you could post a picture.
David Billington

I measured the tap. The TPI are both 16. The smaller diameter is .565" with my vernier, 9/16" is .5625, just a hair different. UNC is 9/16-12, UNF IS 9/16-18, BSW IS 9/16-12 and BSF is 9/16-16. So it is BSF.
The larger diameter is .656 which equals 21/32. I have not found a 21/32 tap, but I only looked in 4 places. If there are bushes available that are pre-threaded, care must be taken to aline both pieces with a pin before brazing or it will not thread in. Does anyone out there know the type of material the bushes are made from? The tap is from an older (and I am 67) MG guy about 25 years ago. Have no idea the source. I also have a factory style reamer for frog kingpins that folks say doesn't exist. photos to follow. My photos are too large. Have to figure out how to make them smaller.
J Bubela

J Bubela
Can you look, please, on the shanks of the taps. The sizes are usually engraved there.
Alan
Alan Anstead

I'm still trying to upload photos. They are too large now. The tap has no markings on it. The label on the case: "705 - 9/16" not very helpful.
J Bubela

J Bubela,

You can find utilities online for resizing images if you don't have one on your platform or email me an image at mgbbs( at )metal-arts( dot )co( dot )uk and I'll resize it to a suitable size.
David Billington

Sorry for the quality. I tried. My camera wouldn't work. Had to use my phone. Not exactly a high tech person.


J Bubela

J Bubela,

Thanks for the photo as that shows what I was told used to be used by a guy some 30 years ago that did them himself in the past, a rare beasty. By the way do you also have photos of bigfoot, yeti, the grassy knoll, and the moon landing set?
David Billington

I am not at liberty to release those, but I still would like to know if the bushing were made from a special alloy. It would seem reasonable to make the pins from a softer material so they could be renewed with out wearing out the bushings. Wishful thinking.
J Bubela

J Bubela,

If I had to guess I would have a punt at a medium carbon steel but that is a guess. As the bushes are brazed in that will soften most steels and I wouldn't expect it to be anything special. If you can get a sample of an original bush it may be possible to get some idea of the steel grade by heating and quenching to see how it hardens or if you're lucky and know someone with the kit get it analysed for it's basic composition.
David Billington

Many years ago (25 or so???) when I was involved with the MGCC midget Register I organised a visit to the archives at Gaydon, primarily so we could look at the chassis records but we could also ask to see any drawings. Is it still possible to access the archives? If so, you could see the relevant drawings and material specs.
Jonathan Severn

This thread was discussed between 10/03/2018 and 13/03/2018

MG Midget and Sprite Technical index

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