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MG MGA - Thread size enquiry

Hi all,
I have just made a start on my winter project which is the strip down and rebuild of my front suspension.

I have just removed the the anti-roll bar and I have found the front threads on the Rt link rod (which bolts onto the front wishbone) are a bit cut up.

I'm fairly sure that the thread is UNF, the thread diameter is 0.5" and the threads are definitely fine.

Does anyone know if I have this right?

I hope to be able to buy a die to clean the threads up and it would be preferable to be able to order the correct one.

Cheers
Colyn
Colyn Firth

Definitely 1/2" UNF on my ARB links. I'd recommend a Clarke set of UNF taps & dies. The threads on the tap and die holders are really too coarse but you can live with them. I found them essential in my restoration ............Mike
Mike Moore

Thanks for that Mike,
I didnt want to just take the chance and send for a die only to find that it was the wrong one when halfway through attempting to re thread the link rod.

The tap and die set has been on my wish list for a while now and it is bound to be useful again in the future.

Cheers
Colyn
Colyn Firth

Colyn, Get a set of thread profile gauges, come in various sizes and both imperial and metric, cheap as chips and get the right thread every time.
David k Brenchley

That's a good idea David, l wonder if Machine Mart sell those as well as the tap and die sets?

I took Mike Moores advice and bought the Clarke set that he recommended.
I have just used the 1/2" UNF die on the thread of the link pin and it has cleaned it up perfectly. I also ran the same size tap through the nut and both are now like new.

Thanks guys

Colyn.

Pic of nut and cleaned up thread reunited and now an easy fit again.


Colyn Firth

looks like there is already a thread pitch gauge in that set Colyn.

You will need to establish if its a metric or imperial gauge or both, you will also need a conversion chart to convert the number tpi into the faster size.

I have a simplified version of one like this laminated which sits on my garage wall. Let me know if you need a copy.

http://www.baconsdozen.co.uk/tools/conversion%20charts.htm
John Bray

I have just checked the set out John and you are correct, it is a thread pitch gauge, one half is metric and the other imperial.
Hopefully it will help prevent me from asking even more unnecessary questions in the future. :-)

My Dad (who would have been 101 years old last year) would be shaking his head at my lack of engineering knowledge. He was an engineer through and through, I think "British Standard Whitworth" was his second language.

Cheers
Colyn

Colyn Firth

Hi Colyn, my Dad is also an engineer and is still writing books on the subject (Stan Bray).

He brought me a thread pitch gauge together with a set of taps (taper, plug and bottoming for each size) many years ago because he got fed up with my repeated requests for 'could you just make me one of these.......it won't take you long!' and yes he struggles with my lack of proper engineering knowledge.

Both our Dad's of course come from a time when BSW threads were common before the UK, Canada and America agreed on the Unified-series to avoid problems encountered during WW2 of having to supply fasteners and tools in both English and American threads.
John Bray

Colyn, Your Tap and Die set looks very nice.
It should have been a Christmas pressy.
Over the years, thread forms on MG's have been a real challenge for the spanners in the tool box. I read somewhere that William Morris used a French machine to make his bolts. something to do with Hoskish-the French engineering firm that produced his first engines--- they could not meet his production needs, as was also the case in the Radiator manufacture. So he bought the business-moved it to England and increased production.
Pre-War and "T" Type engine and transmission components up to about 1952 used this French metric diameter and this un-usual very fine thread pitch of 1MM. These cars used BSF threads else where on the chassis, etc. Electrical fittings used BA [British Associated ] threads.
Whitty spanners fitted each of these hex head bolts & nuts
The 1mm fine threads pulled out of Alli. sump castings very easily, causing head aches to repair . An awfull thread form.
As I see it, in about 1952 BMC changed their thread forms to imperial UNF and witty for castings. Easy. Similar to U.S. Autos.
SAE spanners then fitted these nuts.
Then the 1.5MM pitch threads seemed to be adopted my the auto industery generally, including the Asians.
So, now its metric spanners.
The Germans and French always used metric sizes and 1.5mm thread pitchs.
Its progress, is it not?
When tightening bolts down, go for it, until the arthritis hurts in the elbow--then back it off a quater of a turn. You won't strip any bolts with this method.
I.W. Cowen.

Certainly when I did my home rebuild a far more basic tap and die set was used extensively. Must get a thread gauge too.

As an aside another item that was worth its weight in gold was a cheap hex socket set. I used to hammer them on rusty nuts and almost everything came undone. Abusing a cheap tool seems wrong but....

Paul
Paul Dean

quote.....When tightening bolts down, go for it, until the arthritis hurts in the elbow--then back it off a quater of a turn. You won't strip any bolts with this method.....end quote

Expression in the uk used to be....'up to shear and then back a flat'
John Bray

Most common Japanese thread are 8 by 1.25 with a 12mm head and 10 by 1.25 with a 14 mm head.
The Europeans use 8 1.25 with a 13mm head and 10 1.50 with a 15mm head.
I used to hate finding a 13 mm nut or bolt on a Jap car. Showed that someone ignorant had been there before me. Never did reuse them.
Americans use both.
So much for metric "standardization"
R J Brown

Paul,
You have reminded me that I used to keep a high quality steel metric 12mm socket that I could hammer onto the wing fixing set screws on my previous FHC.
They were 1/2" AF size but they were rusted down a little and the 1/2" AF socket would just slip off under pressure.
Cheers
Colyn
Colyn Firth

Colyn
That's an interesting variant to just go for an effectively undersized 1/2 AF. Hopefully I will never have to do this trick again unlike when car was a rust bucket. What amazed me was the durability of the cheap sockets and the abuse they took over and over again.

Paul
Paul Dean

This thread was discussed between 07/01/2017 and 10/01/2017

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