Tool to remove B31 oil tank filter (swinging arm)

[sergeantpluck]

What tool do I need to remove the oil tank filter on a swinging arm B31?

I don't have a big enough spanner, so need to buy one, but despite hours searching pdfs of owner's manual, service sheets and parts list can't seem to find exactly what it is I need.

I'm thinking of buying a large box spanner - the width across the flats appears to be 1 1/4" or possibly 1 5/16 (32mm) but can anyone confirm the correct size?

Thanks in advance.

[ANDY HIGHAM]

same socket as the fork top nuts

[sergeantpluck]

Thanks Andy.

Of course this now leads to the question "what size socket is needed for fork top nuts?" but I have found one site which says they are 1 5/16in which agrees with my measurement, so I'll go with that.

[JulianS]

You need a socket 3/4 whitworth 7/8 BS size. It is not an AF size.

[ANDY HIGHAM]

I have just measured mine, it is 32.85mm
a 33mm socket will be fine if you cannot find a 3/4"BSW socket

[sergeantpluck]

I have now loosened the oil tank filter nut.
In case it helps anyone else, this was my experience....

- Bought what I thought was the proper tool, described on eBay as a "copy of" a BSA fork top nut / C-spanner.
This fitted fine, but I couldn't shift the nut.
When I slipped on a box spanner to increase leverage the tool just bent!

- Then bought a 33mm socket spanner (from a specialist tool shop - the largest size B&Q keep is 32mm!)
With this I was able to loosen the nut quite easily.

So all now appears to be well, although I won't actually drain the oil until we have a dry spell so I can get the engine warmed up nicely first.