MGB & GT Forum

This topic relates to my 1964 MGB roadster. I wanted to adjust the SU HS4 carburetors. First step is to slacken the levers on the interconnection rods such that each carburetor can be tuned independently from the other.
Here is where the problem started: the nuts are so tight that I was not able to get them loose. I believe that a previous owner has also struggled with this, as the nuts were slightly damaged.
The second problem is that I could not find a proper spanner for these nuts. Metric does not fit (8 mm too small, 9 mm too large), and SAE doesn't fit (5/16" too small, 11/32" too large). What is the correct size spanner for these?

Meanwhile has the scope of my project changed: I decided to take the carburetors from the car and clean them as they were very dirty and greasy. I bought a new throttle & choke kit from Burlen. However, the choke lever is not included in this kit, so I want to transfer it from the old rod to the new one. Which brings me back to the previous problem: I need to slacken those nuts in order to remove this choke lever.

For entertainment: attached is a photo of the connecting rods which were mounted on the car. The original LH and RH levers are of a much nicer design than the ones which came in the new kit from Burlen.

According to M-E the nuts should be 2BA so that's the spanner you need

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Superpro. Nut and bolt rebuild 2010 - 2015. Tartan Red.

GT: 12/78. VW Golf guards, flush fit front and rear valances, frenched indicators, Mk1 rear lights - LED lights. 'Worked' Rover V8, Monsoon ECU for EFI. Commodore VSV8 GM4L60E, Lokar tiptronic shifter & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.

I learn something new every day. This is the first time to hear of a xBA specification for nuts and bolts. I will research for a spanner which is specified for 2BA.

Yeah well I looked up the nut on M-E and then asked Bing "what spanner for 2BA?" I changed mine on my HS4s to 3/16 (or was it M5) eons ago.

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Superpro. Nut and bolt rebuild 2010 - 2015. Tartan Red.

GT: 12/78. VW Golf guards, flush fit front and rear valances, frenched indicators, Mk1 rear lights - LED lights. 'Worked' Rover V8, Monsoon ECU for EFI. Commodore VSV8 GM4L60E, Lokar tiptronic shifter & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.

Barrie is correct.

I have a combo open end wrench w/ 2BA & 4BA. I knew the larger end fit those fasteners and was about to comment that they were 4BA (wrongly assuming that 4BA was larger than 2BA).

Here's a link to a table of wrench sizes Dave DuBois created (now graciously hosted by Dave Braun).

https://www.dbraun99.com/Dave%20DuBois/Wrench_Size.pdf

Thanks Paul! I'm printing that. It should be in the MGE library.

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After being cut for the 9th time, I stopped using Occam's Razor.

Dave Braun has a treasure trove of information on his site. When Dave DuBois passed away, Dave B archived his technical writings so they would be available in the future.

Here's a link to all if Dave D's MG related work.

https://www.dbraun99.com/Dave%20DuBois/

I have used small Imperial sockets on those SU connector nuts with no problem. Don't recall what size, and probably a bit of a mismatch, but they worked fine. This was on a 1962 TR4 with original SUs. Earlier cars may have different size fasteners. I did recently buy a set of BA open-end wrenches and 1/4" sockets - so I could finally work on those ^$%#*#* control cable stops, which are BA2 and BA4. They fit like a glove. Wrench set is Elora, made in Germany, and the sockets are Koken, made in Japan. Very expensive, but having exactly the right tool is sometimes the only way to go.

Thank you. I found a similar table online: https://rroc.org.au/technical/V_Extra_Nuts_Bolts_Key-5046.pdf

Clever move, to replace those bolts and nuts.
I can't find a suitable spanner in shops or online near here. So I started looking for an old 8 mm spanner which I could sacrifice to enlarge to 2BA. Lo and behold I found a 2BA spanner at the bottom of my toolbox. I don't know how it got there and it must have been there for 40 years or so. But it is surely convenient to have it.

I now remember that I replaced all the SU interconnectors with new ones on my 62 TR4, and those were probably 3/16" or something similar. In any case, I recently acquired full sets of BA wrenches and sockets. Brit motorcycle mechanics need them, and that was my source.

The SUs are the only components I've come across that are BA or Whitworth. Everything else I've wrenched on is Imperial. I'd just change the nuts per above, albeit I've found those nuts don't need to be very tight anyway.