Motorcycle Builders – Air Cooled AJS V4 Engine

Air Cooled AJS V4

Air Cooled AJS V4Motorcycle builder is a term we often use around here but it's becoming more apparent it doesn't do justice to the full range of skills and capabilities found among "builders."

An article in the November 2006 issue of The Classic Motorcycle caught my eye, it's actually the story of the motorcycle engine shown on the cover. The engine in question is an air cooled 50 degree 495cc SOHC AJS V4, an engine that was never sold to the public but was raced by the factory in 1936. A few years later, in 1939, the factory produced a liquid cooled V4 they entered in a couple of races and one lone example remains in the Sammy Miller museum. The air cooled version, though, is long gone, last seen about 70 years ago, and that's where this story of motorcycle building begins.

Dan Smith is a Canadian well known in certain circles for his work on old Vincents among other old marques and some 20 years ago Dan developed an interest in the extinct AJS V4 and this is where the story gets interesting. Without any hard parts to restore or measure but only a black and white photo and a cutaway drawing as a reference, he made himself an engine.

So, just how did he do that? To start, Dan did some sketching and scaling based on the photo and drawing, though he soon found the drawing inaccurate due to the artist's attempt to make the picture look right. He took measurements from the liquid cooled version in the museum but found it completely different from the air cooled version. So he was left with the few dimensions he could determine to use as a starting point and, being both determined and extremely skilled, proceeded to recreate the entire engine, from scratch. He made wooden patterns for casting the cylinders and cases, machined bevel gears and many other parts, chose a few select pieces from more modern engines, like pistons from a Suzuki DR100 and the end result is a complete running AJS V4!

Like I said, the general term "motorcycle builder" doesn't quite convey what we're talking about here, maybe motorcycle re-creator would be more appropriate. Superb work!

Link: The Classic Motorcycle
Photos: The Classic Motorcycle

Related: 1919 Excelsior Motorcycle Restoration Project


  1. todd says

    I barely have enough time to adjust my valves. Where do these people get all the resources to do these things?

  2. Rafe03 says

    What a beautiful piece of work! At a regular 2000 manhours per year for the average working stiff, there’s probably 5 years of steady highly skilled labour in the engine alone, never mind getting it into a period frame.

    Fancy showing up down the caf with one of these engines in a good frame. Say a Manx Cafe Racer! Definately not a DeltaBox. Now imagine adding post classic bits (disk brakes, tires, Rob North frame, etc.)

    Ah!, the power of one mans imagination, determination, skill, & resources! What a world we have at our feet.