Help with engine disassembly

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Feb 6, 2005
I recently purchased a '71 Commando 750 and am just getting started on a total rebuild. I am running into a problem in removing the head from the cylinder, specifically in removing the nut from the upside-down stud at the rear of the cylinder. It appears to be a 1/4" Whitworth size, and to date I have scrounged up a spare 1/4" open-ended wrench and ground down the thickness of the head so that it will fit in between the fins on the cylinder. However, despite my tool modification I'm having great difficulty in actually getting the spanner to slide onto the nut. Any suggestions from anyone? Is it truly a 1/4" Whitworth fastener, or has my effort so far been for naught? I'd hate to do more serious grinding on the spanner to attempt to get it to fit if in fact the nut isn't even 1/4".

Any help from anyone?


I used the ring end (12 flats) of a cheap 13mm combo wrench - it fit perfectly after having the outside of the ring ground down to fit.

Funny enough the open end of the wrench does not fit ~ the nut fit perfectly in my 1/4ww socket when removed.

I have a couple of 1/4 whitworth ring spanners which work well here. One I got from Domiracer years ago and looks like the old "starter/generator" box end. That is, it is shaped like a broad "C". The rings have thin walls necessary to fit this nut. The angled handle allows you to turn the wrench with some decent leverage. I'm sure Tony and Jonathon still have some and most Norton parts suppliers do too.

The other one I have is an old Triumph wrench that is a short, thin walled ring spanner that works well and will swing between the barrel and the air filter, but has very little leverage for breaking loose a tight nut. I don't know where I picked this one up.

I would avoid an open end wrench here as you can easily round off the flats and the proximity of the stud to the barrel means you can only get a few degrees of rotation before the wrench hits something.
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