gearbox top bolt spacer

it goes between the top box mounting a engine plate. on the right side. If you have no gap . you have a dominator shell

no sorry i miss-read i was talking about a 750

Michael, this is the arrangement around the top gear box mount on my Mk2A.  Looks like the washer goes inside, between the gearbox and the cradle.

Regards

Richard P

I have dozens of samples to measure...

All NHT engine bosses are 3.31"+/- wide

All NHT AMC gearbox bottom bosses are 3.31"+/- wide

All Commando TOP gearbox bosses are 3.18"+/- wide

difference 0.13 +/- for the commando washer

0.125" is typical for a good spacer washer

Last year.  Some owners found there wasn’t enough room to fit the spacer, others found it was a loose fit.  Consensus seemed to be that the cradles may be slightly distorted.

Is there a serial number on your gearbox shell? If so, what is it?

As Tony Gill has pointed out, if there is definitely no room for the correct washer then you do not have a Commando shell (and, if memory serves, will struggle to remove it from the cradle while the engine is present).

As Tony and Julian have pointed out, if there is no room for a spacer then it's probably a Dominator casing.

Your number is very close to the number on my 1961 99SS Dominator.

My Commando has the top spacer fitted between the gearbox casing and the inside of the cradle.

The Commando gearbox number is stamped across the top mount (and is the same as the frame and engine).

.. the reason for the spacer and slimmed casing on the Commando was to allow the casing to clear the engine plates (or maybe the securing stud for the adjuster) so it could be removed without difficulty.

Something to look out for -- if the box, did in it past life live in a dominator. You most likely will find .the centre stand spring scar on the front of the case

Quite often owners forget to replace the top mounting washer and then torque up the bolt / nut.  This consequently squeezes the gearbox plate inwards and distorts it. Hence some owners later  finding there is not enough of a gap for the spacer.

Sometimes one tends to 'peddle' rubbish information-Here goes. I own a featherbed Commando. The engine and gearbox is 1970 Commando. And the owner (me) had never seen or understood said washer. So over 100,000 miles I wondered from time to time the ally engine-plates split. I remade them and carried on. Eventually I learned about said MISSING washer. I measured the frame engine plate mounts, and the rear mounts of the Commando engine and ascertained that the gearbox top had a problem. Thick washer sorted it. So I would say fit in here what ever it needs. Although the Commando is 50 yrs old I can't see why it should have a Doomy Gbox.

commando internals. fitted in a dominator main shell. 

Good of you to take the trouble to measure the boss widths David, but there is a simpler method - if the top and bottom bosses are the same width : no spacer required; top narrower than bottom : use spacer.

As for why use an old shell, well I've done it. Matter of what was to hand. Agreed the later shells are stronger and, if money were no object, the gold standard would be a Quaife. I'm told those currently sold by Andover pretty good.

and if it is a Dominator-type casing, it could of course be machined to suit a 0.125 inch washer, if you want easier future removal.

Commando gearboxes have a couple of weak points.

The original Layshaft ball bearing used to die quite quickly and sometimes ruin its housing.  The cure for this (if you caught it in time) being a roller conversion.  

Also the gearbox shells were prone to cracking between the respective Layshaft bearing and the Mainshaft Sleeve gear housings.  Welding seldom worked as a cure due to heat distortion.  See attachment.

Lastly......... One extra suffix digit would make that gearbox a Commando part.