AJS & Matchless Owners Club

Hi all, could anyone tell me if there is any information, in one place, that lists the modifications/improvements, to the engines from year to year, looking to find oil flow/lubrication modifications and performance modifications, also, can older crankcases etc, be upgraded easily to accommodate those modifications, regards.

Oh crikey, there seem to be loads! I will try and compile a list of what I've been able to find out...

This seems to be the most comprehensive description of the late-model changes: That round of modifications seems to include the higher capacity oil pump (4.48mm stroke, +38% displacement) as well as the additional oil spray to the cam followers. The right-hand case is different and can be identified by the extra oil gallery (see this post). Don't fit a long-stroke oil pump to the earlier type of case, or it'll bind.

The pre-1961 Lightweights (both 250 & 350) had a particularly tiny exhaust valve. This was subsequently enlarged and remained unchanged for the rest of the model run.

All CSR models appear to have a 1 1/8" carburettor, steel flywheels, a revised inlet port and a bigger 1 19/32" inlet valve.

In addition, the 1965/66 CSRs have a higher compression (9.5:1) piston, up from 8:1 on the earlier CSRs.
At some point, the valve springs changed from hairpins to coils - presumably also for 1965/66.

My CSR has a bigger-diameter crankpin and a single row of 1/2" crank rollers. I think this is the Alpha replacement, as the original one has two rows of rollers on all models, 2 x 10 rollers on the basic models and 2 x 14 on the CS, CSR and 350s (that have the bigger crankpin).

Changes to the few CS models are more complicated and seemingly even less documented. The last of those had a bonkers 10.5:1 piston and presumably other changes to keep it in one piece. The late CS internals seem to be the basis for the CSR, albeit with a lower compression and improved oiling.

All 350s and CSRs have a duplex primary chain, other models are simplex. Early CS primaries use a fatter, single chain, later ones are duplex.

At some point (1964?), the adjustable oil feed to the cylinder head was deleted and blanked off. Internally, these later cylinder heads have no oil holes above the rockers, visible with the inspection cover removed.

Internally, the double ball-bearing arrangement on the crankshaft drive side should have long since been replaced with the superior arrangement of a ball bearing on the outside and a roller bearing on the inside.

I think that's all correct. Anybody know any more?

There are three different breather rotor arrangements. the early one had the breather tube threaded into the casing but just pressed into the stator (these often came loose and rattled around mimicking a big end rattle) the mid one had the breather tube threaded into the stator and was therefore more secure and this can be used as a direct replacement for the early one (a complete engine strip is required to repair the original type or fit the mid type) . The latest incarnation had no breather tube at all but just a drilling in the casing where the tube on the older models would have been and the stator was held in place by a bolt through the casing, this one is not inter changeable as the casing is different.

On the subject of exhaust valves the later models had an exhaust valve with thicker stem to prevent breakage, you can modify if you get the later valve and matching guide. The early lightweights had a stepped headlamp rim which reduced the size of the headlamp to 6". Never seen one of those steel billet type flywheels though as shown in the engine diagram??

The very early 350's like mine had a washable gauze oil filter...

Good list, Paul! I'd forgotten about the various breather arrangements.

Here's a picture of the billet steel crank:

Thanks, that's the same as mine... thought that was the "standard" crank? The reason I mentioned not seeing a Billet steel crank is because of this article attached below (check out the crank in the picture and the comments below left) anyone seen a crank like this?.

Hi, thanks for the post`s, i am hoping to compile a documented file of the various AJS 250cc models from 1958 onward, with regard to specifications/modifications including photographs/sales brochures etc and whatever i can find in the way of parts books/manuals, have found some information on google already, such as a documented/photographed description of a gearbox overhaul, some history, but tends to cover all models rather than the lightweight on its own, can i ask members to keep going with the post`s, to me it is all interesting and certainly helps in my quest, best regards.

Will you be sharing your information?

Here's what the standard cast iron flywheels look like: They are easy to identify because they don't have the counterbalance holes.

Hi Janet, as i get to grips with all the relevant information and can get it in to some sort of order, anyone wishing to view would be quite welcome, as you will appreciate i am starting from scratch on this, but have already approached, various suppliers and asked what they may have regarding old posters/sales brochures or in fact any information relating to the model 14, i feel sure that with assistance from members of the club and outside sources, i will get there in the end, regards.