The MGA With An Attitude
FASTENERS with Odd Threads - CF-104
At 01:11 PM 6/6/05 -0600, Will DeDalis wrote::
>"Is their a list of Whitworth used on MGA and B, brake abutment, crank pulley, front wheel hub nut?"
There are precious few Whitworth fasteners on the MGA (maybe none), and even fewer on the MGB (also maybe none). Most of the threads were standardized to Unified National thread standard during WW-II, and MGA design and production came later. Most threads are UNF (Unified National Fine), functionally interchangeable with SAE standard threads. Some threads in soft castings are UNC (Unified National Coarse). In the aluminum gearbox the bolts for starter motor and remote shift extension attachment were coarse thread for early cars and fine thread for later cars. For some double threaded studs the bottom end will be coarse threaded and the top end fine threaded. This has a functional purpose to allow the nut (shallow ramp angle) to be tightened while the stud (steeper ramp angle) does not turn (cylinder head bolts for instance).
Screws in the Auster windscreen assembly are British BA series, mostly 2BA for the smaller ones (although some intermediate aftermarket service parts may have #10-32-UNF threads).. The wing bolts to secure the top frame to the windscreen are 5/16-22-BSF (British Standard Fine). Some small screws in the SU carburetors may have BA standard threads, maybe also the wiper motor. The starter pull switch, starter input post, control box and fuse box grub screws are all BA series, which appear to be inch size but with an odd pitch. All of those applications are a holdover from designs and parts in production which pre-date WW-II. Some threaded plugs in the sides of the engine block and oil pan may appear to be 12mm, but are actually BSP(S) (British Standard Pipe, Straight threads). Side fill and bottom drain plugs in gearbox, rear axle, and fuel tank are tapered pipe threads.
You do not need any metric or Whitworth wrenches for the MGA. I have never owned a single Whitworth wrench. To be more complete, the SU carburetors are originally per-war design, so they have some BA threads and a few metric hex sizes. These like to call for Whitworth spanners, but the hex fittings can work with an adjustable wrench in a pinch, and will seldom need to be touched on the road.
However, .... Some recent production aftermarket hydraulic hoses have metric dimension wrench hex fittings (what we get for having them made in a foreign country). Not long ago I received from Moss Motors a set of clutch cover to flywheel bolts with proper 5/16-24-UNF threads but 12 mm hex head. These apparently had the 5/16 inch threads cut onto a standard 8 mm screw blank. Close, but no cigar. This disturbs me to no end when I have to find a metric wrench to work these non-standard fasteners, even though I bought them from a reputable British parts supplier expecting original specification.
One more item caught up with me recently. I had installed a Mitsubishi alternator in my MGA. The main mounting pivot is done with through bolts, so no problem. One bolt at the adjusting ear had a 8mm female thread, and the bolt had a 12mm hex head. I needed to adjust the fan belt once on the road, didn't have the 12mm wrench in hand, and spent a few choicer words on the adjustable wrench as I was skinning knuckles. Next day the cure for that problem was to drill out the 8mm female thread and install a 5/16-24-UNF Heli-Coil. Now my Japanese alternator uses 1/2 inch wrenches all around, and I still don't carry any metric or Whitworth wrenches.
Addendum June 1, 2018:
As time progresses, more and more British car parts are being sourced from countries other than the UK or USA. One of the more recent issues is Lucas changing hands to become TRW-Lucas, with TRW sourcing stuff from China. Therefore the new replacement Lucas alternator has a metric thread for the adjuster bolt. This is another case where I drill out the thread and install a Heli-Coil to change to 5/16-24-UNF thread as original, so I don't need another metric wrench in the traveling tool kit.
To add insult to injury, some of the "foreign" sourced parts are changing head size on bolts. I recently bought a Chinese made Lucas alternator with 8-mm threaded adjuster hole. Not being convenient to drill it out for a Heli-Coil at the moment, I bought a small pack of 8-mm hex head bolts, and a 12-mm wrench socket. The new bolts had 13-mm hex head rather than 12-mm, so it seems the Chinese can't even get that right, and I had to exchange the 12-mm socket for 13-mm.
The next recent example is the cable stop for the heater water control valve. As original both the cable stop and the "P" clip holding the cable jacket has 5/16-inch hex head screws, so you could use one nut driver for both fasteners. The latest issue cable stop now has 6-mm (very loose 1/4-inch) hex head screw, so now you need two different wrench sockets to make one cable adjustment. Get used to it I guess, since these screw-ups seem to be happening a lot faster than we can scream foul and call for fixes.
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