Tuesday 11 January 2022

The AJS 33/7 Trophy Model Restoration: First Assessment

It is now the 2nd 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!


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