Stuck Sump Plug

All you need is a very large box spanner, bear in mind this is Whitworth. Chances are somebody has a large 1/2 drive socket or even a 3/4 drive socket! (used on trucks a while back). You do NOT need to take the engine out, in fact having it in the bike should hold it steady enough for this job.

7/8" Whitworth

e.g. https://www.zoro.co.uk/shop/tools-and-machining/impact-sockets/7-8inch-whit-impact-socket-3-4inch-square-drive/p/ZT1007131X

Need to grind a bit off the sides with the angle grinder to clear the cross member but works a treat:

BERGEN 38mm 3/8" DR LOW PROFILE OIL FILTER SOCKET B3066 | eBay

1 1/2" AF as your in the USA 

That is the correct size in the US of A, Peter. AF..

Other translations are:

Pet cock = Petrol tap.  (1/4 BSP in this case)  British Standard Pipe.

Gas = petrol. (Use Marine grade in the US of A = E0)

Happy riding while you can. 

Commando sump plugs  and sump magnetic drain plugs as now supplied certainly dont fit any of my Dominator whitworth tools . So likely to be AF .  I resized them for my Dommy so i dont have to carry AF as well as whitworth.

You can also get it off with a suitable sized pipe wrench (plumber's tool). Take care not to scuff the crankcases. And I know folks here will be horrified but that's what I first used on my '70 Commando back in the day; that too had the earlier frame with the cross tube towards the back of the engine.

I was hoping somebody didn't mention that way of getting the sump plug out.... the pipe wrench works fine, careful to not bure the nut. I am not sure where you are Robert in this post but the large brass nut under Dommie/SS/Atlas/Early commando must be Whitworth. But going back to the original problem, it does need a decent fit socket/box spanner (somebody hold the bike and a 3ft bar!) As for 38mm socket, yes this might work. If the socket is a snug fit on the drain nut then 'go for it' I can't see how any thread will strip? A new nut is just buy and fit, a stripped thread in the crank case is an 'OH sh1t moment' Have fun.

take the head steady off, remove the front engine mounting off . raise the rear wheel off the ground. With a bottle jack and a block of wood . jack up the engine. this will allow sump plug to tilt forward and a socket a good if . I DID THIS LAST WEEK

Sump plugs can be heli coiled. (Like most threads)

Drain Fuel tank and half the oil tank and lay the bike over onto some cushions etc.

Perfect access. Been there and done it.

Are you trying to scare the poor boy? Stripped threads, removing Isolastic mounts? It's just a bit tight, get a large pipe wrench with an old fork stanchion (or similar) over the handle, remember to turn it the right way (RH thread) and it'll come off clean and easy. No damage, no problem. This is a routine service operation, you don't have to take the bike to bits!

If people did not unecessarily dismantle their bikes ,where would we find those lovely basket cases ?  Dont be a spoil sport Stan !!.

I have a set of three Ridgid pipe wrenches, very useful in difficult bike or car related problems but easy to damage surfaces.

Adjustable flat jaw Ridgid Hex Wrench as in photo is better, was excellent in the 70s for the sump plug and fork top nuts, wish I still had it. Eddie's socket solution, WD40 and a heat gun my modern choice on tight threads. 

WD40? I find that Plus Gas is better and doesn't leave the oil residue which can be a nuisance some time. Do not forget that Alex Simonson is in that large country over the pond! But if he must  buy a 'foreign' bike then he must expect the need for 'foreign' nuts/spanners. Even us who 'nearly know what we are doing, run foul of the Whit/AF/Metric horrors from time to time as any owner of a commando will tell you. It was all a matter of costings at the factory in the 70s.

once you have found the right size, as an extra tweak, grind back the face of it if it has rounded entry to the hexagon,  to get a sharper edge.