The AJS 33/7 Trophy: Preparing the Gearbox and Clutch

The Sturmey Archer EIV gearbox that I had chosen to put into the bike needed some work before it could be used.

The starting point for the gearbox was an EIV casing – there was nothing inside - which I had acquired some years ago.  Luckily, Norton bought the rights to Sturmey Archer gearboxes in the early 1930s when SA ceased manufacturing gearboxes. I say “luckily” because Norton then had these gearboxes made (by Burman) in large numbers and they also didn’t change much, at least initially, which is useful when it comes to finding parts as they are both plentiful and fit. Up to this time, the positive stop mechanism had been an external “bolt-on” item positioned just above the gearbox casing (the picture below is on a 33/10 - the 500cc version of the bike)

but a redesign by Norton put this inside the casing but with an external linkage

 both of the above pictures courtesy of Bonhams

 ….and the Dolls Head gearbox was born, although the "head" is more pronounced on later versions of the 'box.

The Sturmey Archer/Dolls Head gearbox is well designed and extremely strong; I used a close ratio DH gearbox some years ago in my JAP-engined Levis sprinter and apart from having to face-off the dogs on one of the gears to prevent it jumping out of gear, it never gave a problem. The entire gear cluster and the selector also conveniently fit into the EIV gearbox shell and as I had a spare Dolls Head gearbox (minus the  positive stop mechanism – I had already “borrowed” that for the V-Twin project), I figured that I might as well have the rest of the internals.

All the gears and shafts were in excellent condition and standard ratios.

There is another difference that I am aware of between the EIV and Dolls Head gearboxes, namely the EIV gearbox has a bush on the drive-side end of the layshaft whereas the DH gearbox has a bearing. The bush in my EIV casing was worn and so, rather than replace the bush, I machined the casing to accept a bearing.

There was also quite a bit of wear on the final drive sleeve gear bush, which tends to wear rather than the mainshaft. This was pressed out and a new one made and pressed in:

before final machining to size.

The gearbox was now essentially complete and it was time to turn attention to the clutch ….except that I didn’t have one.

Anyone in the UK that reads my blog will know the meaning of the expression “if it ain’t broke don't fix it”  ….for anyone that is not a native English speaker this translates as “if something works, then don’t change it”. Norton adopted this philosophy in a fairly major way and this is why a clutch from a 1950s Norton Dominator and a final drive sprocket from a Norton Commando (which was introduced in 1967) fit the splines of an early 1930s Sturmey Archer gearbox. I have also just checked the splines on a mainshaft that I replaced on a mid 1920s Sturmey Archer CS gearbox on one of my vintage Nortons and that is also the same.

I needed to have a shock-absorber in the transmission and as this isn’t going to be on the crankshaft or the rear hub, it has to be in the clutch. The Norton shock-absorber clutch is compact and well designed and the first step was to purchase a new “spider” that fits onto the mainshaft (this is the part that drives the shock-absorber) to check wear on the splines.

Absolutely fine; and so the next step was to find a clutch. Various modifications were made to the Norton clutch over the years it was in production – and it was also fitted to AMC bikes (in fact, Sturmey Archer developed a shock-absorber clutch long before the design was acquired by Norton – see the 1931spares manual). To avoid ending up with a collection of incompatible parts it is advisable to acquire a complete clutch rather than trying to make one up from separate bits. A quick search on ebay found a complete Norton Dominator clutch ….unfortunately on a US listing:

Rather than wait until one came up in the UK I bought this one. Unfortunately I had to pay 70 GBP postage plus another 70 GBP VAT/Excise duty/collection fee to get it delivered! Whilst I appreciate the need for taxes to oil the wheels of bureaucracy I really object to paying 50 GBP “Value Added Tax” where the value that was added occurred over 60 years ago, somewhere around 1960, when it was manufactured and fitted to a bike that left the Norton factory and for which Purchase Tax would have been paid at the time. Anyway, rant over ….I have a clutch.

Upon stripping, most of the clutch was in pretty good condition although it was pretty obvious why it would have stopped working!

I don’t know what level of abuse that you would have to give a clutch to break off all 3 vanes of the shock absorber spider in this way.

With lots of new bits - rollers for the bearing, shock-absorber rubbers, bonded lining on the backplate and friction and plain (surflex) plates the clutch was ready for reassembly.

I'm sure there is already plently written on this, but just a quick note on inserting the shock-absorber rubbers: I put in the larger rubbers and then held the spider on the splines of an old mainshaft in the vice. Using a clutch locking tool on the clutch centre splines for the friction plates and, with a length of exhaust pipe for extra leverage, I could easily compress the rubbers

to simply pop in the smaller ones.

The clutch is now as good as new.

The final bits to complete the preparation of the gearbox are a new Norton Commando final drive sprocket for a 5/8’’ x 3/8” chain and LH thread securing nut and washer. The Commando sprocket has a narrower hub than the original and a spacer has therefore been made to avoid the sprocket fouling the gearbox casing and to get the chain alignment correct.

The gearbox and clutch are now ready to be fitted in the yet-to-be-made engine plates.

The AJS 33/7 Trophy Model Restoration: First Assessment

It is now the 2^nd week of January 2022 and I have 2 bikes – the AJS V-Twin and the Velocette Thruxton - awaiting better weather for road testing. I am hoping that these won’t consume too much of my time in the coming months and so I have started on the next project. Yes, it’s another OHC AJS and the most modern one (1933) of these that I own.

For anyone interested in the origins of the post-vintage OHC AJSs, this article – The Cammy AJS, published in 1965 provides an excellent short summary up to the advent of the 7R.

This is what I have:

and this is how it appeared in the AJS brochure of the day:

It is always useful to find an illustrated spares manual for any restoration. The depictions of the parts is extremely valuable in determining what should (or should not) be present and, as the little illustrations are often quite accurate, what the part should look like. Here, I am extremely grateful to the Danish Jampot guys (the large rear shock-absorbers fitted to post war AJS/Matchless bikes were referred to as “jampots” ....see the picture below, which is a Matchless G80 Competition Model that I restored many years ago and shows "jampots" on the rear suspension

….hence the association with the marque) who have thoughtfully collected many period manuals and brochures on their website here and the illustrated parts manual for this bike, the 33/7, is available here.

First, the significant parts that I know to be correct:

-     The frame, forks, hubs, petrol tank, oil tank, engine structure (crankcases, barrel, head, cambox, both oil pumps, carburettor and crankshaft (from pictures provided by the vendor), camshaft and drive), battery carrier, rear mudguard stay (by comparing with the parts list and a number of unrestored bikes sold at auction), stand, new and well-made exhaust pipe

And the parts that are either incorrect or missing:

-     Gearbox (it has been fitted with a Burman BAP gearbox rather than a Sturmey Archer), megaphone exhaust instead of a silencer, mudguards, wheels and tyres, no electrics, incorrect and earlier magneto that fouls the bottom of the carburettor

Other observations:

-     Somebody has been quite exuberant with a drill – the front hub, front engine plates, top fork links, petrol filler cap (!!) look like pieces of swiss cheese.

The period brochure (for the 1934 model) provides further useful information:

A few more observations upon stripping:

Although they fit the engine and frame mounting points correctly, the rear engine plates are incorrect and, I can only assume, have been remade to allow the Burman gearbox to be fitted.

A Sturmey Archer EIV gearbox would have been originally fitted. By a stroke of luck I have one of these in my “store” and inserted it into the available space.

The final drive sprocket can be aligned easily by positioning the gearbox appropriately although none of the holes in the engine plates are in the right place. As with other bits of the bike, there are a few too many holes in the engine plates and it looks like someone had a few attempts at getting them in the right place. New engine plates need to be made but at least I can use the existing plates as templates for the front and rear mounting holes.

Another observation while stripping the bike was that the crankshaft mainshaft has a taper, seen below,

rather than a splined shaft that accepts a crankshaft shock-absorber. My earlier cammy AJSs all have crankshaft shock-absorbers and the parts manual shows a splined mainshaft to accept a shock-absorber (and also the shock-absorber bits), highlighted in the box below

and so I can only assume that the mainshaft has been machined at some stage, possibly as a result of damage. A solution will be needed for this.

As previously mentioned, the magneto is too tall and fouls the bottom of the (correct) carburettor

and the handlebar hangers are massive bronze items – they look like they were made to support some major structural part of the Titanic.

A first look inside the engine reveals that the Weller chain tensioner is about 1 ½” too short

although it is a relief to find that the castings and threads are all in excellent condition.

And, although the rear mudguard stay appears to be original, it has fractured and the  2 parts are held together with a twist drill rammed inside the tubing!

Oh well, plenty to keep me occupied for the rest of the winter months!

 

The AJS V-Twin: INDEX PAGE

The links below are in chronological order of the AJS V-Twin Project to aid navigation of the blog.

The AJS V-Twin Project

Where to Start….?

The Crankcases – Part 1: Start of the Patterns

The Crankcases – Part 2: Completion of the Patterns

Machining the Crankcases – Part 1

Machining the Crankcases – Part 2

Machining the Crankcases – Part 3

Machining the Crankcases – Part 4

The Chassis

The Camshaft Drive

The Timing Case Patterns

Timing Case Machining – Part 1

The Chain Tensioners

The Cylinder Heads

Camshafts, Bearing Housings and Vernier Adjusters 

Timing Case Machining – Part 2

Oil Pumps

Wheels, Gearbox and Chain Alignment

Engine Plates

Fixing the Gearbox in Place

Carburettors and Inlet Manifolds

The Clutch: Part 1

The Clutch: Part 2

The Positive Stop Gear Change

Exhaust Rings

The Mudguards and Oil Tank

The AJS V-Twin Crankshaft: Part 1 – Determining the Stroke

The AJS V-Twin Crankshaft: Part 2 – Connecting Rods & Pistons

The AJS V-Twin Crankshaft: Part 3 – Design of the Flywheels

The AJS V-Twin Crankshaft: Part 4 – Machining the Flywheels

The AJS V-Twin Crankshaft: Part 5 - Mainshafts

The AJS V-Twin Crankshaft: Part 6 Assembly and Assessment

Footrests and Rear Brake

The Lubrication System

The Exhaust System

The AJS V-Twin Petrol Tank ….and Petrol Tanks from India

Completion of the Dry Build …the last little odds and sods

The Last Jobs before Rebuilding

The Final Build of the AJS V-Twin: Part 1

The Final Build of the AJS V-Twin: Part 2

The Final Build of the AJS V-Twin: Part 3

The Final Build of the AJS V-Twin: Part 4 – Last Part

The AJS V-Twin: First Start

The AJS V-Twin: First Road Test

The AJS V-Twin: Postscript 

The AJS V-Twin: An Oil Cooler and Cambox Modification 

More Work on the V-Twin