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MG TD TF 1500 - Why do we have Whitworth

Explanation of threads.

http://www.classicandperformancecar.com/features/theknowledge/282730/the_knowledge_screw_threads.html

Jim
James Neel

Great article. Thanks James. Corrected a misconception I've always held. I'd always believed BSC stood for British Standard Coarse but in fact it's short for British Standard Cycle. The only error I could spot was the statement that;

"BSF (British Standard Fine) has the same thread angle as Whitworth but a finer pitch and smaller thread depth. Like Whitworth, it can be found on many British cars up to the 1950s, especially on precision components in the engine and gearbox."

On our cars BSF is used on the body while the engine & gearbox threads are Metric with Whitworth heads, which is enough to confuse anybody. Cheers
Peter TD 5801

P Hehir

OK Peter, a quiz, the nut and bolt that hold the radiator stay and the lower stay to the bracketing the firewall aren't labeled in the Moss catalog. The one on the left side of my '53 TD fits a 5/16 W wrench and appears original (or at least correct) but the one on the right is a common 1/2 SAE nut and bolt. In a moment of genius I decided to replace the right one with one of the head studs I replaced with Tom's superior ones. They also fit a 5/16 W wrench. The stud won't go through the holes. On more careful inspection I see that the threadt on the "good" bolt are finer than those on the head stud. SO:

What is the correct nut and bolt for the stay bracket at the firewall??

Thanks. Jud
J K Chapin

The correct nut and bolt for the stay bracket would be a BSF. The head stud won't fit through the hole is a 10 X 1.5mm. Peter's last sentence says it all (also derisively know as Nuffield's Mad Metric). There is a long story to that, being as the XPAG engines are a bit of a refinement of an old American engine that was turned over to the French and then taken to England during WWI to keep it from falling into the hands of the German's. See the chart, XPAG/XPEG Engine Fasteners in the Other Tech Articles section of my Homepage at: http://homepages.donobi.net/sufuelpumps/

To add further confusion, the rear axle fasteners on the later TD and the TF are American threads, Unified National Fine, or in todays terms SAE fasteners. Cheers, Dave
D W DuBois

Not sure Jud but I have no reason to doubt Dave & would defer to his greater knowledge in this area. I believe the wheel nuts on later TD's & TF's were also UNF. My front hubs have been replaced by a PO so I have two wheel braces, a UNF one for the front & a BSF one for the rear, so when removing wheels I have to be very careful to keep the nuts separate. Cheers
Peter TD 5801
P Hehir

"I believe the wheel nuts on later TD's & TF's were also UNF."

That is correct, the lug nuts front and rear where changed at the same time that the rest of the rear axle fasteners were changed. That change took place Dec. 10 1951 at car number 12285. Interestingly, it wasn't until Dec 13 1951 at car number 12419 that the lug nuts on the spare carrier was changed from BSF to UNF (or SAE). That means that 134 unfortunate owners had to carry two different spanners in order to change a tire. As an aside, I have two front brake drums with the BSF lugs on them. Cheers, Dave
D W DuBois

Ok, hate to be dense but does that mean that a 5/16 by 3" long (Moss 320-895) is what I need? I'd really like 3-1/2 but I don't see that listed. Thanks. Jud
J K Chapin

Jud - You said earlier that the bolt has a 5/16" head, unless it has two different markings on the wrench - something like 5/16W - 3/8BSF. If the wrench is marked 5/16 only (or 5/16W) then the bolt is going to be a 3/8" BSF bolt. Your best bet is to measure the diameter of the bolt before getting a new bolt. Cheers - Dave
D W DuBois

I think the reason for the Metric threads in MG engines and gearboxes started after WW!.
Morris Motors didn't have their own engine / gearbox plants originally, but bought components in and assembled them.
One of the components has been an engine made by Continental in USA, but after the war they switched to engines made by French company Hotchkiss in their UK plant. The engine was loosely based on the Continental but of course had metric threads. Later on, Morris bought the Hotchkiss factory to make Morris engines. Since all MGs used modified Morris engines and gearboxes, they inherited the metric threads, even in designs that had nothing to do with the original Continental.
R French

R French - You've got it! Below is an article written by Jerry Felper of Vintage MG club of Southern California regarding the origin "Nuffield Mad Metric" fasteners.

THE ORIGIN OF THE XPAG ENGINE
Jerry Felper

Did you ever wonder why the threads on a XPAG and XPEG engines are French Metric or where this great engine came from. Well here is the whole story.

It all started in Connecticut in 1826 with the birth of Benjamin Berkely Hotchkiss. Benjamin served an apprenticeship as a machinist and worked in the Sharps Rifle Factory. He participated in the development of the early Colt Revolver.

In the mid 1850, he and his older brother returned to the family business, where the two spent their spare time experimenting with cannon shells. Hotchkiss projectiles were especially lethal and after proving themselves in the Mexican War, small orders came from the U.S. government and Japan. With the advent of the Civil War, their new enterprise grew into a giant. By 1865 they were filthy rich.

Their problem was that peace kept breaking out, so Benjamin traveled to Europe in search of additional markets. Here he met Napoleon III. Emperor of France, who sensing a threat from the East persuaded him to set up an armament factory in France, this was 1867. It was located in St. Denis, also home of the famous boiler and steam engine builder Delaunay-Belleville.

France was soundly trounced in the Franco Prussian War and it was not until 1872 that the new Hotchkiss gas-operated automatic "rapid- firing" gun, the first modern machine gun, was adopted by Chile, China, Britain, Russia and the USA. By this time there were five Hotchkiss factories operating in Europe.

When peace broke out again, Hotchkiss found themselves with too much production floor space and not enough production. By this time Benjamin died and there were a number of creative Presidents of Hotchkiss. In 1898, President Mr. Parsons figured that any company that could turn out precision gun parts could just as well turn out parts for the new auto industry. By the turn of the century, the slack on armaments had been taken up by large component orders from Panhard and De Dietrich. Parson hired George Terrasse who was an experienced auto designer and Hotchkiss started to build autos.

One of their first cars had a 19L Engine. Their autos had many state of the art features and were very reliable. Now the connection with our engines starts. Hotchkiss built autos until the First World War broke out and were back making guns. The French decided it would be best to move the Hotchkiss armaments factory to England to keep it away from German hands. The plant was moved to Coventry.

After the war they needed some thing to build, since they saturated the machine gun market. They built 1,100cc engines for BSA and in 1921 they took a contract with Morris to build copies of the American Continental engines that were originally built for the Morris Cowley.

This proved to be a big operation and 1923 William Morris purchased Hotchkiss-Coventry.

Editor's Insert: Since the factory had been moved from France, all the tooling was French Metric. It was considered too expensive to convert all the tooling to British specifications. So Leonard Lord came up with the idea of using Whitworth heads on the metric bolts and nuts so British mechanics could use their regular tools on the engines. Thus was born the "Nuffield Mad Metric" nuts and bolts used on all engines and transmissions made from 1923 thru 1956 in the now Morris Coventry engine factory.
The overhead cam engines used in the early MGs all were this strange combination of French Metric threads with Whitworth heads.
In 1936 MG adapted a Wolseley overhead valve engine for the new series MG, the TA

This is where the XPA- series engines came from and why they use French Metric Threads. Our engines were derived from copies of an engine of the 1920s, built by Continental in the USA (The Continental engine was a version of the engine designed before WW I by William Morris).

If you would like to read more about Hotchkiss please get a copy of Skinned Knuckles Vol. 30 No.] A UG. 2005, Foreign Affairs by John Kuerzi. This is where most of my information came from and l thank Skinned Knuckles for allowing me to copy much of the article.
D W DuBois

Dave,

The one sentence ""Nuffield Mad Metric" nuts and bolts used on all engines and transmissions made from 1923 thru 1956" is somewhat misleading.
All Triple-M engines and transmissions built from 1929 to 1936 all used BSF fasteners. I can't speak for other years until post-war when certainly the fine thread fasteners with BSF/BSW heads were used. These Triple-M engines were built by Wolseley and are a derivative of the Hispano-Suiza Type W4a aircraft engine.
So not all MG cars used the somewhat perverse Mad-Metric fasteners.
Lew Palmer

Lew - I think you are correct. In Neil Cairns booklet, Engines for MG's Their Story after 1935, the chart in Chapt 3 - The 'X' Series of Morris Engines shows them coming into being in 1938. Cheers - Dave
D W DuBois

This thread was discussed between 01/10/2014 and 13/10/2014

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