AJS 350

1924-1926 350cc (2¾hp) AJS

(AKA. Bits & Pieces)

B3 Catalogue Picture

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 –

DSCF0001 - Copy

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.

16 comments on “AJS 350

  1. Bruce says:

    Drop me an email on Kirby.bruce “at ” gmail.com

  2. Robin Otto says:

    Dear Colin,
    Thanks for your Email.If Bruce still has the ’24 frame and forks available,do let me know.
    Went to the Banbury run and saw a couple of very nice Big Ports.+ Cricket bat Norton and
    Sunbeams (I love the early OHV tt models from around 1924,but did not see any.

  3. Robin Otto says:

    I am looking for anything to make up an early(pre 1925) Big Port.Does anybody have anything available for sale ? Write to me,at robinotto@btinternet.com

  4. Bruce says:

    Phew! I have a pretty rusty 1924 frame and forks lying in my shed doing nothing – but I’m in South Africa!

    • Colin De La Rue says:

      Wow! Let me think about this for a bit! A genuine ’24 frame & forks would solve a lot of my problems but as you say in South Africa – that creek crossing is a bit of a challenge. I will look into transport.
      Colin DLR

    • Robin Otto says:

      Hello Bruce,Do you still have these parts? Can you send to UK?

      • Colin De La Rue says:

        G’day Bruce. I am up and about again and paying attention to motorcycles! Much as I would dearly love to have a genuine 1924 AJS 350 frame, I cannot sort out a reliable way to get it to northern Australia.
        Coupled with this is the fact that I am now 75yo. and my work has slowed down a lot, even on my high priority jobs. I think I should relinquish priority to our new correspondent Robin Otto.
        If the two of you can work out something that will get a Big Port on the road, good Luck to you!
        Colin DLR

      • ROBIN OTTO says:

        Dear Colin, Thanks for your Email. I am replying directly as I am not quite sure how to post comments on your website. At the moment I have a Norton Cricket Bat that I must restore.Could do with an early ES2 engine (1928-29) if you ever hear of one Good luck with your superb Norton. Cheers, Robin Otto


      • Bruce says:

        Can send anywhere – it’s just the cost that’s an issue. drop me an email on Kirby.bruce@gmail.com

    • Swen says:

      Hello Bruce, can you contact me by mail, I am interesred in your frame and fork. Flattank@yahoo.de.
      I am staying about 3 month the year in ZA Normaly Joburg area.

      Thanks Swen

    • Paul willsher says:

      How much for the frame and forks . I will pay shipping to texas USA

  5. art carty says:

    i have a ajs big port motor mostly complete except timing cover mag stirrup one nut push rods and rocker assm i would like to at least make the motor complete thanks art

    • Colin De La Rue says:

      A pity Art; All parts that I have only one (or none – ’24 push-rod) of myself . But I keep searching
      Colin DLR

  6. ewen mitchel says:

    i have been restoring a1924 model for about 6 years its almost done to concours standard if u want to get in touch with me i am on 01356622597 callafter 6 my name is ewen cheers

  7. Colin De La Rue says:

    G’day Nick,
    ‘Big Port’ heads are in the hen’s teeth category, but I may be able to help with Burman gearboxs.
    I will email you with more detail.
    Colin DLR

  8. Nick Hawtin says:

    mate im am looking for some 350 big port heads>?? do you know of any and also burman gearbox bits?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.