Gearbox Mounting

[RichardS]

I am putting together a bitsa and havea couople of AMC gearboxes, but can not find any engine plates that match the mountings. The serial number on both 'boxes starts N... does this indicate it's for/from a Norton? And more specifically, did Norton 'boxes have different mounting centres?

The centre distance between the two mouning holes (on the 'boxes I have) is 7.74", just under 7-3/4"; the AJS/M engine plates seem to be 7-3/16" (7.1875") centres.
Checking through the spares lists I deduce that the AJS/M AMC 'boxes had the same mounting centres as the Burman B52, since the same engine plates are listed for both types.

I find it odd that they used different AMC 'box cases between AJS/M and Norton, but stranger things have happened.....

I'll get alloy plates water-jet cut anyway so it's not a crucial point, but I was expecting to use a standard engine plate to get the dimensions and nothing seems to match what I have - not an uncommon event .

Can anyone confirm the mounting centres of an AMC-Matchless gearbox?

[Reynard24]

“N” gearboxes are for Norton models built before 1962, after that they have “NA” on them. AJS and Matchless boxes use “M” and “MA” in the same way. I believe a Norton box will fit in the engine plates but it ends up at a very strange angle - there is a post on here somewhere from someone who fitted one.

[RichardS]

“N” gearboxes are for Norton models built before 1962, after that they have “NA” on them. AJS and Matchless boxes use “M” and “MA” in the same way. I believe a Norton box will fit in the engine plates but it ends up at a very strange angle - there is a post on here somewhere from someone who fitted one.

Thanks,
That's remarkable, but does essentially confirm what I have found. As you say, waving the 'box about lining either lug with a hole does put it at a very strange angle.
Oh well, it's a bitsa anyway, just more than I'd realised, and a bit more work than I'd thought.

[RichardS]

Well I'm darned, who'd a thunk it? Yup, here are a couple of pics, my Norton box first

IMG20230527160511.jpg

And this Matchless box from the WWW

M-AMC box01a.jpg

That makes it very clear why nothing seems to line up!

So, do I make strange engine plates to match the N 'box, or see about getting a Matchless case? I'm on the fence having just stripped, serviced and reassembled the Norton 'box. Not a big deal, but an annoyance.

[SPRIDDLER]

If you use the search facility for the Forums entering the search keywords Norton+gearbox you will find some of the articles refer to compatibility.
My memory may be faulty but it's worth comparing the mainshaft exposure length outside the casing as I recall an old post that mentions having to make a mod otherwise the clutch sprocket and the final drive sprocket may not align the chain correctly with the engine drive sprocket and the rear wheel sprocket.

Search facility is here:

Search new website.jpg

[Joker_Bones]

IMG_20230801_233743.jpg

The width of the mountings is a couple of mm different.
The offset of the mountings across the width of the case is a few more mm different.
The angle of the mounting relative to the gearbox is different.
The centres of the mountings on the matchless case is 181mm approx.
I swapped everything into the matchless case.