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.

There are variations of below available......worth considering as options if correct size. 

... I'd recommend myself. A cheap set is likely to be made of poor quality steel, and they're generally hardened all through making them brittle. You's likely to end up with the remains stuck in the hole.
I prefer Al's suggestion of a correctly sized box spanner with a long bar on it.

There was the suggestion of a 38mm socket, as the nut is 38mm across. My observation is a snug socket and a 1/2 drive bar. Due to the size and material (Brass?)  of this nut then |I wouldn't even consider a reverse thread extractor, I have had more failures with such extractors than successes.
Or a large box spanner, a snug fit should shift and a long bar should shift it.

Are there different threads on sump plugs? Have a new non fitting one.

Alexander, if you have access to welding apparatus, this may be a way out. Back in the late seventies, money was tight for me, so I botched up this wrench out of some scrap steel strip and pipe. Still use it. The hexagonal part could have been made a little lower. 

I like Bennie's suggestion and this is the kind of tool I would have fabricated as an apprentice.
Some of the Commando sump plugs were made of steel so I suppose a bar could possibly be welded directly onto this. 
I am not so sure that a thread extractor would work on a sump plug. Either Steel or Brass.

From past experience of trying to pull out a gearbox drain plug that had welded itself to the casings I would be a little worried about the thread in the case pulling out.  Apparently this was due to the effect that modern synthetic oils sometimes have on Aluminium, Steel and Blass component combinations. Stainless Steel and other metals are equally notorious for such.

hello,

   which way to undo nut.                                                                       
                                                                                                                                                                         barry

The best way to deal with rounded hexagons is to use Metrinch spanners and sockets; not cheap but worth it, and of course cope equally well with metric and US sizes (sadly, not proper imperial hexagons, though).

https://metrinch.com/metrinch_en/hand-tools.html

well done!
  However, that was on much too tight! One thing to learn is : how tight are fastenings required to be: huge variation on Commando.
   Also when to use nyloc or equivalent nuts, or the right type of Loctite, or copper washers in this case, or fibre washers elsewhere.
   A LOT of people have been there and done it already, which means plenty of experience to lean on, after leaning on the socket bar!!

Section "A" of the Workshop Manual for Norton Commando 750/850, from all good spares outlets.
Covers most of the fastners.
Doesn't cover the primary case though.
I'd use a setting for an ordinary 3/8 unf nut with a spot of threadlocker as back up.
 

Big fan of Greg Marsh's site in the USA- torque plus lots of other good information, good pictures of rebuilds  and his standard of restoration is top notch

GME - Norton Info Home (gregmarsh.com)

Hi, suggest carefully drilling a small hole through and across 2 of the adjacent flats of the sump drain nut and wire lock to a convenient fixture, will only need nipping up and remain secure.