1935 AJS V4 Replica
By Robert Smith
1935 AJS V4 Replica
Engine: 495cc air-cooled SOHC 50-degree V4, 50mm x 63mm bore and stroke, 10:1 compression ratio, 40hp @ 6,000rpm (est.)
Carburetion: Two Amal with dual remote floats
Transmission: 4-speed, chain final drive
Electrics: 6v, DC generator, dual twin-spark magneto ignition
Frame/wheelbase: AJS “Denly” single downtube steel frame/55in (1,397mm)
Suspension: Girder fork front, rigid rear
Brakes: SLS drum front and rear
Tires: 100/90 x 19in front, 100/90 x 18in rear
Weight: 450lb (205kg)
Seat height: 29in (737mm)
Fuel capacity/MPG: 5gal (19ltr)/NA
The word “unique” has a simple meaning: it means there’s only one of a kind. Things can’t be “quite unique” or “almost unique.” Either they are or they aren’t. Take Dan Smith’s AJS V4. It’s unique. There’s only one. And that’s because Dan built it himself.
Many of us can turn a wrench to do basic bike maintenance. Some of us are capable of restoring a rusty barn find to its original state, perhaps even making parts where the originals no longer exist. But very few of us can build a complete motorcycle engine from bare metal.
With the aid of drawings, a capable machinist could probably shape the parts from billet using CAD and a CNC mill. But what if there were no drawings, or even a model to work from? That didn’t stop Dan, who designed, cast, machined and assembled his V4 from a black-and-white period photograph and a cutaway sketch of the 1936 prototype. Oh, and if you didn’t know AJS built an air-cooled V-4, you’re not alone!
A little AJS V4 background
The Wolverhampton firm of A.J. Stevens earned a solid sporting reputation during the 1920s with their racing “Big Port” 350cc singles, while also building sturdy side-valve V-twins for sidecar use.
Unfortunately, the financial collapse of 1929 scuttled AJS, and the rival Collier Brothers of Plumstead, London, makers of Matchless motorcycles, snapped them up. Though they had a sporting reputation of their own (a Matchless won the single-cylinder class in the first Isle of Man TT race in 1907), the Colliers intended to exploit AJS’s racing heritage, hence the motorcycle that was the sensation of the 1935 Earls Court show in London: a Bert Collier designed air-cooled overhead cam V4 dressed in AJS livery. It was displayed with lights and generator as a fast road model, but exposed “hairpin” valve springs and space for a supercharger suggested it might be raced too.
The four cylinders were arranged in a 50-degree V with a single camshaft on each head. A central crankshaft sprocket drove a single timing chain, tensioned by an idler between the cylinders. Two carburetors, one on either side, fed the four cylinders (one front and one rear cylinder for each carb), with the exhaust exiting through four separate pipes. Two bevel-drive magnetos hung on the right side of the engine providing the sparks, while a front-mounted DC generator — sitting where, some speculated, a supercharger might fit — fed the battery.
Though it never went into production, contemporary reports suggest that parts for as many as 30 air-cooled V4s were produced. It was certainly raced; the factory entered two machines in the 1936 Isle of Man TT, with Harold Daniell and long-time AJS factory pilot George Rowley as riders, though neither machine completed the course. A racing V4 appeared again in 1938 with a supercharger, but apparently suffered overheating problems. None seem to have survived.
In 1939, AJS entered a water-cooled V4 in the TT and the Ulster Grand Prix: in the latter race it led for three laps before rider Walter Rusk retired with a broken fork link. The “wet” V4 was also raced briefly after WWII, until a ban on superchargers terminated its development and the parallel twin “porcupine” took its place.
Dan Smith and the AJS V4
Vancouver’s Dan Smith is a legend in the Canadian vintage motorcycle scene. A long-time Vincent owner and a guru of the Stevenage machinery, he owns two complete examples: a fully tricked out Series C Shadow with alloy wheels, modern carbs and his own modified “short rod” engine and a Series B Rapide that he’s ridden not only to Tierra del Fuego and most of the way back, but also north to the Yukon.
Dan’s last two restoration projects, a 1934 BSA Blue Star and a 1933 Matchless Silver Hawk, were rescued from almost total obliteration with Dan making many of the missing parts himself. His interest in building the V4 goes back 20 years, though preparation really started seriously in the mid-1990s. “This engine is just fascinating,” he says. Not surprisingly, re-creating a motorcycle that was never much more than a prototype and was last seen nearly 70 years ago took a while.
Dan started with a solitary black-and-white photograph and a cutaway drawing — not an engineering drawing but a line drawing showing the general layout of the engine internals. Vic Willoughby and Bruce Main-Smith in the U.K. provided some useful insight into the V4 project, and Dan also visited Sammy Miller’s museum in England to collect dimensions from the supercharged, water-cooled 1939 race bike.
“I did some sketching and scaling. I had these dimensions, and I couldn’t fit anything around to make it work. After quite a bit of time, I concluded that the water-cooled one was completely new. I was trying to duplicate the crankcase: water cooling would have allowed them to make the engine more compact, with shorter rods. I couldn’t make the dimensions work for the air-cooled engine,” he says.
Dan next attempted to scale many of the components, interpolating angles and dimensions by projecting the axes shown in the cutaway drawing. It seems there may have been some artistic license used so the drawing would look right to the eye, and the angles shown are deceptive. “There are, I think, six different diminishing points,” he says, “so it’s impossible to scale.”
So, starting from the known two-inch bore diameter of the 50-degree V, and allowing a wide enough flat between the bores to accommodate the cylinders, Dan was able to derive the deck heights for the cylinders on the crankcase mouth. Then, by working out the rod length based on the pistons’ dimensions, “I got to an accommodation of numbers I could use,” Dan says.
Designing the bevel gear drives for the twin magnetos was a challenge. With dimensions taken from the water-cooled engine, it proved impossible to fit gears with the right number of teeth with the 50-degree angle between the two magnetos. Dan settled on spacing the magnetos at 60 degrees, which gave room for the bevel gears. The half-time speed for the magneto drive is achieved through two reduction gears.
Next, Dan made a full-scale model of the engine in wood and fitted it with a period Burman gearbox into a “Denly” AJS frame. The Denly-style frame was developed by Norton/AJS racer Bert Denly, who added a third chain-stay to the standard AJS frame to increase its rigidity, running from the seat tube to the rear axle mount.
Now Dan could start on making the major castings, producing the patterns from which the components were cast. With the crankcase dimensions fixed, he was then able to put together the crankshaft, flywheels and camshaft drive. Though the original V4 was said to have used six main bearings for the crankshaft, Dan only saw the need for five.
“I don’t know why they’d need six,” Dan says. “In order to keep it narrow, you don’t want to put two bearings on the drive side. It’s only maybe 40 horsepower at 6,000 rpm and perhaps 40 pounds of torque.”
Dan used two inboard main bearings in the crankcase, two outboard of the flywheels and one in the timing chest to prevent end float. Next came the connecting rods. “It’s a knife-and-fork rod like a Harley,” says Dan. “I had to make those, work out the cranking ratio and establish the rod lengths.”
Next came the top end. Here, Dan used pistons from a Suzuki DR100. “I consequently ended up copying the combustion chamber, and I also used their cam profile,” he says, adding, “but the cams are individually verniered with pins, like a Manx.” The valves are turned down items of Vincent heritage. “I was going to make valves, then it dawned on me, I have old Vincent valves by the bucket load around here, so I re-machined them.”
Dan has incorporated eccentric rocker adjustment. “The V4 used alloy rockers, so that’s what the replica has,” he says. There are also small pumps to scavenge oil from the cam boxes back to the tank. “I had to make those too,” he adds.
The single timing chain runs from the central crankshaft sprocket, over one camshaft, under an idler sprocket between the banks of cylinders, then over the second camshaft. The chain itself is from a Suzuki GS400 — or rather, from two GS400 timing chains riveted together. Like the other Suzuki parts used in creating the V4 (and the hairpin valve springs from an NSU Max!), the chains were supplied by ex-racer Murray Neibel of Vancouver dealership Modern Motorcycling.
For the magneto drive, Dan not only cut the bevel gears himself, but also made the gear cutters. And though it took him a month to finish them, “it made a beautiful fit. I’m really happy with how they came out,” he says.
The magnetos themselves are both by British Thompson-Houston: the rear mag is a BT-H KDTT donated by local ex-motocross racer Denis Mitchell. The forward mag was an eBay find and came from Tasmania. Remarkably, the name plate is stamped “KDV 50 AJ4,” though Dan thinks it’s unlikely to be a reference to the V4.
As well as the magnetos, the timing drive spins the gear oil pump borrowed from a BSA A10, with the worm drive taken from a B-series BSA engine. An anti-wet-sumping valve and pressure relief valve complete the lubrication system.
Dan chose two float bowls for each carburetor as contemporary reports suggest the V4 may have suffered fuel starvation problems. If so, Dan hopes this will prevent it.
The last component to be cast was the primary cover. “I didn’t have that until [the engine] was in the frame. I thought, OK, the crankshaft’s here and the transmission’s here, so now I can draw the primary case. You look at the photograph and it’s really just joining the lines,” he says matter of factly.
By April 2006, Dan’s re-creation was essentially complete and “dry” assembled, though the cams still needed to be indexed. Before that, Dan had to dismantle everything for painting and plating. Oh, and work out the carburetor settings, ignition timing …
The V4 lives!
On July 8, 2006, just over 70 years since the its progenitor had run in the Isle of Man TT, Dan’s V4 burst into life with a throaty rasp from the four exhausts — not smooth like an inline four, but with a ragged beat not unlike a Laverda triple. It’s a magnificent machine, and a wonderful realization of Bert Collier’s creative vision. The Thirties were a time of great engineering advances, and the AJS V4 represents perhaps the pinnacle of that decade’s motorcycle design.
Very few machinists have the foresight, ingenuity and skill to pull together such a project, and I know I’m not alone in appreciating Dan’s efforts to recreate one of the era’s most significant motorcycles. MC
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