Saturday 19 September 2020

The AJS V-Twin Project

I wish I could pinpoint the moment when I decided to do this project. I have plenty of projects-in-waiting (8 in fact – 5x Mk1 cammy Velos, 2x Big Ports and a 33/7 OHC AJS ….oh, and I nearly forgot, a Velocette Thruxton that I need to bring back to life) but after I had completed the AJcette project, with which I was very satisfied, I decided to use more of my stock of early Velo bits and make a V-Twin version. This is another decision-on-a-whim that has, so far, engaged me for more than a year of my life.

In addition to the complete project Velo bikes, I have also acquired many Mk 1 cammy bits and pieces over the years. One often stumbles across these purely by chance. One day I was at my grit-blasters premises getting some bits cleaned up and I just happened to mention Velocettes and he immediately said that another of his customers had mentioned to him that he had some Velo bits that he wanted to get rid of. I phoned this guy – he only lived about 5 miles from me and, sure enough, he had bucket-loads of bits. My luck was in - they were all Mk 1 OHC parts - crankcases, barrels, heads, crankshafts, camboxes, bevels, pistons – including a lot of racing pistons with huge domes ….and so I bought the lot. He had no connection with Velocettes and I have no idea how he came by these parts. His hobby was collecting Sinclair C5s so maybe he was planning to develop a go-faster kit…

Now, making an OHC AJS V-Twin would not be an entirely original idea because AJS made a one-off of such bike in 1930 for an attempt on the world speed record. The engine is essentially two 500cc R10 cylinders/heads/camboxes on V-Twin crankcases. The project has been recorded by Steven Mills in his excellent book “AJS of Wolverhampton”, which documents AJSs history up to the time they were bought by the Collier brothers.


There is also a good precis of the history of the bike subsequent to the speed record attempts here

One can only imagine how awesome this bike must have appeared (and sound!) to onlookers 90 years ago.

Interestingly, and apart from the obvious differences of being a V-Twin, the details of the internal design are identical to the single cylinder counterpart from which it was derived, although the rear cylinder head is a mirror-copy of the front head to avoid the rear exhaust interfering with the front carburettor.


Acknowledgements to whoever owns the copyright of the above 2 pictures.

The engine started life as naturally aspirated (as in the above picture) but, following its first failed attempt at the motorcycle land speed record (it made around 130 mph), it was supercharged. This increased its top speed only marginally and it failed again at the land speed record (those pesky Germans kept going faster) and it was eventually sold and ended up in Launceston, Tasmania. In fact, I was on holiday in Tasmania in February 2020 and tried tracking down anyone that might have a recollection of it but I think this history is now lost. The garage when it “lived” is now a coffee shop.

It ended up back in the UK in 1981 and was restored and now resides in the National Motorcycle Museum. Will it ever be seen (and heard!) running again?

And so this was the project on which I embarked. It would not be an exact copy and it wouldn’t be 1000cc but I would try and make something that closely resembled this amazing looking bike.  

The idea, in its basic conception, would be to use 2x Mk1 OHC Velocette cylinder barrels, heads and camboxes and to make the rest of the engine. A chassis and gearbox etc… would then be added to make the rest of the bike. What could be simpler….?

This blog is now the story, in detail, of how this project evolved.

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