1924-1926 350cc (2¾hp) AJS

(AKA. Bits & Pieces)

The 1924 catalogue picture above is really included by way of misdirection. What I have is Dad’s ‘heterogeneous conglomeration of inconsequential desiderata’; a range of bits & pieces of mid 1920’s 350 AJS’s, referred to by certain dull and soulless individuals as ‘a heap of rubbish’. In fact, this is what it really looks like decorating the end of my shed –

The bits & pieces:

1924     B3 “Big Port” engine (The “High Compression Sprint Model”) – largely complete.

1924       Side valve engine – partial only.

1925       Overhead valve engine – largely complete.

1926      Side valve engine – largely complete.  No. H80634

The engine numbers are not available in most cases, as at that time AJS stamped them on riveted-on brass plates on the drive side of the crankcase. These plates seem to have readily got lost.

Here we have a sample: (The 1924 “Big Port” is on the left, a 1926 side valve on the right)

1926 2¾ hp. frames –

Nos. G83550, &  G56190.

The two frames are badly pitted and because of the very light thin-wall tube used in their construction they may only serve for static display.

Well…! Dad had an abiding passion for the 1924 AJS B3 “Big Port” which he had campaigned fairly successfully on the dirt-track in 1924-25. He long cherished the plan of finding and restoring one. When I noticed this particular B3 engine advertised for £25 in the Melbourne “Age” in about 1963, Dad had me buy it for him. He was very disappointed with its condition – I had thought it good that the engine was at least fairly complete although its engine number plate is missing. (The engine number on Dad’s dirt track “Big Port’ was 47082; guess what number is very likely to turn up on this engine when I work on it?)

Dad continued to search for parts suitable to construct a “Big Port” (or at least a reasonable facsimile thereof) and gathered up any 1920’s 2¾ AJS pieces he could find. The other 2¾ hp. engines etc, mentioned were acquired through deals that Dad made with like-minded vintage motorcycling and car enthusiasts around the Western District of Victoria.

By various means we have added a number of other suitable parts.  We have a Lucas magneto with the correct AJS Vernier timing adjustment and a not-quite-complete AMAC carburettor of suitable vintage, plus a few other odds and ends. The two frames and various wheels Dad picked up in rubbish tips in the Otway Ranges. (He could recognise any AJS 2¾ part at sight from at least two hundred metres, regardless of condition)

The main ‘lump’ missing is a gearbox, we have only a cracked, empty shell. I continue to gather up any suitable parts I come by in the hope of perhaps finishing his project some time. As Dad carefully preserved his owner’s manual, various tools and parts (even a brand-new tulip inlet valve) and a number of period illustrations of the machine dating from its heyday, the idea is not too far-fetched. I would like to build up the Big Port, or at least a Big Port replica, as a gesture of filial respect, but at present it is very low on my list of priorities.

The ‘Big Port’ was something of a legend in its day; some of the history of the marque is covered briefly in Gregor Grant’s “AJS. The History of a Great Motorcycle”.

Since 1914, AJS had built up a formidable international competition record, including winning both the Junior and Senior Isle of Man TT’s with 350’s in 1921. The B3 was a production sports machine offered in 1924 to capitalise on this reputation. It, in turn, had great sporting success in both professional and amateur events, particularly the burgeoning Australian sport of dirt-track racing.

The sports AJS’s of the 20’s were generally very efficient and particularly light. They had large overhead valves, light flywheels, a thin-wall frame, even having the nuts and bolt heads reduced in thickness to keep the weight down.

The B3 model had a number of the weaknesses of its period; including an alarmingly flexible frame, the weak two-bolt fore-and-aft gearbox mounting and even the ‘trademark’ 50mm bore exhaust port. This latter was really grotesque on a ‘350’.

Pieces of trivia:

• Some dirt track riders found that the frame could flex so badly in the heat of battle that the rear chain could be thrown off. To overcome this they fitted long tubes from the stand bosses at the rear fork ends to the bottom crankcase bolts to give a bit more rigidity.

• It was found by trial and error, that an open exhaust pipe length of 6’ 6” gave an optimum performance.

• Someone, who obviously did not care about the weight penalty, found that a Model T Ford final drive torque tube could be cut down and attached as a ‘megaphone’ rear section of the exhaust pipe, giving a delightful ringing exhaust note.

• It was found by some startled owners that even if the spark-plug lead was detached, a warmed-up B3 at full throttle would continue to run. This was thought to be due to a core of incandescent gas remaining in the ‘tulip’ exhaust valve and igniting the new charge at approximately the right time.