1957 Velocette MAC 350

How did their engineering excellence and originality come about?

The MOV

Success is often born out of failure. In 1931 in the depths of the depression, Velocette introduced a side-valve 350cc single-cylinder, the model “M” to fit in their range between the utilitarian 250cc 2-stroke GTP and the overhead camshaft 350cc KSS/KTS models. Its failure in the marketplace was at least partly because of poor performance. But it did buy time for Works Manager Eugene Goodman and his assistant Charles Udall to come up with a winning, technically advanced design for an overhead valve 250, the Model MOV (M Overhead Valve).

The MOV was to be easier and cheaper to produce, but still reflect Velocette’s engineering sophistication; and it introduced a number of important design features that stayed with Velocette until motorcycle production ceased in 1971. So while the specification called for pushrod operated overhead valves, Goodman and Udall placed the camshaft as high as possible in the engine to reduce moving mass in the valve train — creating the famous “Map of Africa” timing cover. The cams acted on quadrant-shaped followers driving short, Duralumin pushrods running in an external tube to the valves via adjustable rockers. Each valve was closed by two coil springs. Considered leading edge at the time, the valve gear was fully enclosed with recirculating dry sump lubrication.

The designers also tried to minimize the width of the crankcase and therefore reduce flexing. To achieve this, they specified a built-up crankshaft with a taper-fit crankpin and roller main bearings. They also kept the primary driveline as close as possible to the crank, minimizing side loads on the crankshaft and gearbox mainshaft. Operating the 4-speed ‘box was Velocette’s patented sequential positive-stop foot-shifter — most motorcycles of that era relied on a hand shift/foot clutch combination, and many made do with just three speeds.

The MAC

Whether or not Velocette intended the MOV to grow into a family of larger-capacity machines, the MOV’s design became the template for all Velocette OHV singles, and its fundamental “rightness” was demonstrated in that the same basic engine design was retained right up to the final 500 Thruxton. But the most popular engine size for sporting motorcycles in 1930’s Britain was 350cc (500s were usually thought of as sidecar tugs); so not long after the launch of the MOV in September 1933, the 68mm x 68.25mm 250cc acquired a new 96mm stroke crank to create the sporty 350cc MAC.

The MAC engine’s long stroke (40 percent greater than its bore) seems curious now, but was influenced by Britain’s taxation system, which favored smaller-bore engines; and it also avoided opening up the MOV crankcase to accept a larger bore cylinder. Ignition was by BT-H (later Lucas) magneto with fiber gear drive — one of many measures intended to reduce mechanical noise. An Amal carburetor controlled fueling, and a Miller DC generator provided 6-volt electrics.

Both the MOV and MAC shared a similar frame with a single downtube, rigid rear and Webb sprung girder fork at the front. The MAC’s front and rear wheels wore 3.25 x 19-inch tires with 6-inch single-leading-shoe brakes, while the engine produced 14 horsepower for a top speed of 70mph.

1937 models featured an automatic ignition advance-retard for the magneto, designed by Velocette’s Harold Willis, creator of the positive-stop foot-shifter. But war was just a couple of years away: and while Velocette did submit prototype machines based on the MAC (and called MAF) to Britain’s Ministry of Supply, no significant orders were forthcoming.

Post World War II

The MAC was re-introduced in 1946, and fitted with the Dowty Oleomatic semi-hydraulic front fork for 1948. At the same time, drum diameter of the brakes was increased from six to seven inches. Though they worked well when new, and with the correct air pressure, the Dowty fork units were prone to seal failure, and were replaced in 1951 by new telescopics designed and made by Velocette. These featured coil springs and full hydraulic damping.

For 1952, a Welworthy “Al-fin” light alloy cylinder with austenitic iron liner and more extensive finning replaced the cast-iron cylinder barrel. At the same time, a one-piece alloy cylinder head casting with shrunk-in valve seats replaced the iron cylinder head and separate alloy rocker box.

Introduced for 1953 with the provision that such models were initially “for export only” (a phrase familiar to anyone growing up in 1950’s Britain) was a new frame featuring a swinging arm controlled by a pair of Woodhead-Munroe shock absorbers. At the same time, the gearbox was redesigned, a felt oil filter was added to the lubrication system, and a split level dual seat replaced the twin saddles.

Typically innovative, Velocette introduced a unique system for adjusting the preload on the rear springs. The new frame featured a slotted track for the upper rear shock mounts, so that the shock angle could be altered (thus varying the effective preload) by sliding the top mounts back and forth through a short arc.

The MAC remained in the Velocette line-up until 1960 with few further changes, by which time around 25,000 had been manufactured.

Joe Li’s MAC

Though too young to have enjoyed them at the time, Joe Li is a keen student and aficionado of British motorcycles from a particular era.

“The time period I like most about British bikes is the post-war late Fifties, early Sixties,” he says.

Joe’s research showed him that British motorcycles of that time fell mainly into three categories. “At that time, they had bikes for people to go to work, they had bikes that were for learners, and bikes that were favorites of young people for speed and performance.”

Joe concluded that three types dominated: 500 and 650 twins for performance; small 2-strokes for learning or commuting; and big singles for fast road use or sidecar duties. Joe already owned an Ariel Arrow 2-stroke and a BSA A65 Lightning café racer, so he wanted a big British single to complete his collection. Why did he choose the Velocette MAC?

“I didn’t have a specific bike in my mind. I started off by thinking a 500 would be more practical for distances because of the higher speed and higher torque.” Joe considered bikes like the BSA B33 and AJS/Matchless 500s. “I also liked the Velocette 500s, but they were out of my budget. And for a 350 Velocette, the only choice that had the style I was looking for was the MAC. I read that the MAC is a very user-friendly bike. It’s easier to start than the Velocette 500 or 350 Viper.
“Then this 350 MAC came up. It actually cost more than a 500 BSA or AJS, but I have done some research online, and the MAC should be a good bike for what I’m looking for. Most of what I heard was complimentary.”

Joe found his MAC at Eddy’s Motorcycles in Yorkshire, England, (www.eddys-moto.co.uk) and had it shipped to Canada. “When I first sat on it, my impression was that it’s really light, and it’s very comfortable, and the weight distribution is good compared to some other bikes. It is very well balanced.”

How is it to ride?

“It’s very smooth. And it’s not slow at all. The way I use this bike, I like riding around in town, I like riding for coffee or for lunch or visiting a friend. This bike is perfectly sufficient and capable for what I like to do. The first thing I had to learn was the starting process. Once I learned it, it was so easy to start. It’s easier than all my other bikes. Now every time I start it first kick regardless of whether it is hot or cold.”

Aside from some oil leakage from the gearbox and pushrod tubes, Joe is delighted with the MAC.

“I’m very careful with maintenance. It leaks a little bit of oil from the top end and from the gearbox. When I park it, it loses a few drops. I don’t think it leaks enough that I should worry. But if I can make it better, I will. I didn’t expect that it would be completely oil-tight, because I know British bikes … so I don’t feel disappointed about it. It’s just getting used to it.”

Velocettes have a reputation for better build quality than most. Now that he has one, what does Joe think?

“I think that’s true,” he says. “It’s smooth, it has really good brakes, the handling is excellent, and it’s very nimble.” MC

Velocette and the Isle of Man TT

It’s difficult to overstate the importance of the Isle of Man TT races in the eyes of British motorcycle enthusiasts in the 1930s. The TT was the testing ground for performance and reliability, and manufacturers could reasonably expect increased sales from TT success.

And while many British bikemakers prepared special racing machines for the Isle of Man TT, only two were consistently successful in the larger capacity classes: Norton dominated the 500cc Senior class with the International, while Velocette’s KTTs held sway over the 350cc Junior division.

In the 1930s the Junior TT bikes were often within 2-3mph of the Senior machines, and in 1934, Scotsman Jimmy Guthrie actually recorded a faster time in the Junior race than in the Senior, winning both classes. (Guthrie rode a Norton in both, averaging over 79mph in the Junior.)

As street motorcycles were principally sold as transportation, a significant proportion ended up attached to family sidecars. Five-hundreds were often fitted with sturdier frames, sidecar attachment lugs on the frame, and heavier flywheels to preserve momentum. So for solo riding, a lighter-weight, freer-revving 350 was often the preferred choice for the sporting rider.

Significantly, Velocette never won the Senior TT in two decades of trying; yet they won the Junior TT eight times out of 17 attempts between 1926 and 1949. — Robert Smith

Harold Willis

The mercurial genius of Harold Willis produced several important innovations for Velocette. Willis joined the company around 1926 when his father, a prosperous butcher, bought a quantity of shares in Veloce Ltd., the parent company.

Willis first enjoyed success as a rider for Velocette with a number of placings, including runner-up in both the 1927 and 1928 Junior TTs. The latter year saw the introduction of the Willis-designed 4-speed foot-shift gearbox, which eventually gained near universal adoption.

Willis is also credited with the idea for swinging-fork rear suspension. A “spring frame” had been available from engineers Bentley & Draper (fitted principally to Brough Superior motorcycles). Both Vincent and Moto Guzzi also offered rear cantilever springing. But the idea of mounting a forked strut horizontally to a motorcycle’s seat tube and controlling its motion by hydraulic dampers was Willis’ own.

As an experienced pilot and owner of a DeHavilland DH60 Moth, Willis was also familiar with the oleo-pneumatic struts made by the Dowty Company that were fitted to the undercarriage of many period aircraft. The Dowty Oleomatic struts used air in compression as a spring medium with hydraulic oil damping. Willis asked Dowty to supply oleo units suitable for use as spring-dampers for his swingarm frame. These were introduced on the 1938-on Mk VIII KTT race bikes.

Willis also came up with the idea for an automatic ignition advance-retard mechanism to fit on the BT-H magnetos used on Velocette singles at the time. Also gaining near universal adoption in the 1950s, Willis’ system was introduced on the 1937 Velocette range.

No doubt with ideas and innovations still to uncover, Harold Willis died from complications of meningitis in 1939. He was just as old as the century. — Robert Smith