Pre-65 Trials Weapon: Velocette MAC 350

“The lightest, most competitive Pre ’65 Scottish eligible machine possible.”

The Pre-65 Scottish Two-Day Trial is one of the world’s premier vintage trials events, hosted for nearly 40 years in the Scottish Highlands. What started as a few blokes pulling their classic British trials machines out of the shed for a bit of friendly competition has turned into serious competition on equally serious machines. Though rules vary from club to club, pre-65 trials generally allows machines with an engine, gearbox, and silhouette of a frame available at the time.

Back in 2019, we featured an incredible pre-65 Ariel machine from Daniel Dobson and his father, Ed, of the UK’s Ed’s Motorcycles — based in Cumbria. Now the duo are back with Velocette-based trials weapon:

“She was ordered by a customer in Spain and the brief was to build the lightest, most competitive pre65 Scottish eligible machine possible.”

The bike started life as a Velocette MAC 350, but the only original component is the engine — which has been replaced with a highly tuned +410cc unit built by a friend in the trials world.

The frame was built in-house, the same oil-in-frame Ariel replica they used on their Ariel build. It’s been paired with a set of REH forks, CNC yokes, Daniel and Ed’s own custom cast magnesium wheel hubs, titanium wheel spindles, hand-beaten “peanut” tank, and a vacuum-bagged carbon kevlar sump guard!

“This made a lot of the old timers nervous — however, some demonstrations with a separate four-layer layup and a bat eased worries.”

What’s more, the duo manufactured their own set of levers — available for sale to any interested parties — as well as a 1mm titanium purge-welded exhaust and CAD-designed, 3D-printed carbon airbox — bloody trick! And those are just a few of the highlights!

All in all, this has to be one of the trickest vintage trials machines on the planet. Below, we get the full rundown on the build straight from Daniel himself!

Pre-65 Velocette 350 Trials: Builder Interview

• What’s the make, model, and year of the donor bike?

So the bike began life as a Velocette MAC 350 a very long time ago. All that remains of the original bike is the engine, and of that a lot has been replaced/re-engineered. The motor came from another builder who is a friend in the trials world and has been bored out to around 410/420cc and had a complete rebuild to go along with that.

• Why was this bike built?

She was ordered by a customer in Spain and the brief was to build the lightest, most competitive pre65 Scottish eligible machine possible.

• What was the design concept and what influenced the build?

So having the eligibility being the main point it took a few designs off the table. Things like titanium frames are banned and the silhouette of the bike has to be reminiscent of a bike from the era. Other than that, we resided in the fact that this bike will go through scrutineering once, and then there would be new rules the following year to ban some of our material usage. The price of innovation eh, makes it feel like F1 haha!

• What custom work was done to the bike?

From the ground up this bike has been built by us to be as light as possible. From the front we have our own cast magnesium wheel hubs laced into 32-hole rims, titanium wheel spindles, front forks from REH, which are currently the best on the market, CNC billet yokes and yoke spindle.

On the bars we have Renthal trials bars with Domino grips and levers. Moving further back, on the top of the engine we have the hand-beaten “peanut” style tank and on the bottom we have a vacuum-bagged carbon kevlar sump guard. This made a lot of the old timers nervous — however, some demonstrations with a separate four-layer layup and a bat eased worries.

Between the engine and the tank, we have our built in-house, oil in frame Ariel replica frame — this is the same as the frame seen on our previous trials Ariel build.

From there, on the crank side of the engine, we have our four-piece billet clutch back — this took some design time owing to us not wanting to alter anything engine wise with it coming from another builder. So it had to be a clamshell design to clamp onto the machined boss on the side of the crankcase.

The primary drive is a standard chain and sprocket affair, which I wasn’t a fan of, but it was dictated by the customers clutch choice. The clutch is a period AMC four-spring clutch that we refurbished with new friction plates, springs, cups studs and a vapour-blasted and galvanised case and basket.

In the gearbox we went through it top to bottom, replacing all the bearings and whichever gears showed significant wear. All the bushes we remachined in a modern Colsibro alloy which, as we can tell, is the best bush material out there, mainly used for valve guides. In the other gearbox case we machined a new kickstart shaft to take a modern KTM kickstart as a bolt-on instead of having to marry a modern kickstart top with a period kickstart bottom with worn-out splines. To finish before reassembly we had all the cases vapour blasted to get rid of 70 years of schmutz.

With gear levers we decided that there was a looming shortage of original levers, so decided it was time to start remanufacturing. So beginning with a CAD drawing, we 3D-printed a test lever, then moved onto our pattern maker to have a set of casting patterns made and casting 60 brand new levers.

From there we had to have a broach made to cut the splines for a standard Burman gearbox spline and then machine the split and M5 bolt hole with counter bore for the clamping screw and finishing off with a knurled and tapped replaceable tip. We still sell these for anyone interested.

The exhaust routing was something new on this bike. As the engine does not have its ignition unit mounted to the back of the engine like the other bikes we’ve built, we could route through the frame to keep the centre narrow for the rider and avoiding the usual issue of flammable boots rubbing on exhaust pipes. For a silencer we have a carbon tube with a reflective aluminium tape inner coating on the inside to reflect heat.

For tips we have billet machined end plugs and clamping rings with a perforated stainless internal tube wrapped in exhaust packing to deaden noise. Material-wise, the rest of the exhaust is 1mm titanium all purge welded, sprung to engine with a flexible mount to the engine plates.

Under the seat we had a new move for us with a 3D-printed airbox, CAD-designed to fit into our frames. Over the 3D print we have done a single layer carbon fibre wet lay with a clear coat, and in the top we have a billet machined plate to take the fixing points to the frame and the mounting for the filter plate.

The filter plate was something I’ve wanted to machine for a while, taking some inspiration from the cheese grater front to the Mac Pro. While in CAD, I also did an airflow analysis of the airbox to try and maximise the airspeed into the carburettor and avoid the usual air flow problems which plague old airbox designs.

Speaking of the carburettor we have gone with a brand new Amal Concentric in 22mm.

Above the airbox we have an aluminium seat with the embossed V for Velocette — this was originally intended to be a carbon seat, however after some mould failures we went for aluminum in the interest of time as this was a very long build. However, with using our frames on multiple builds, when we get the seat mould finalised, we can make the seat and ship it to the customer in Spain for him to fit.

Finally in the rear we have another magnesium wheel hub, again laced into a 32-hole rim and rock shocks taking up the beating from the sections.

• Can you tell us what it’s like to ride this bike?

Currently still in the break-in phase for the engine, so all the riding has been around our yard making sure oils are getting to the right places and that they stay where intended, despite British manufacturing’s best efforts.

• Was there anything done during this build that you are particularly proud of?

The carbon was a new direction for us, a brand-new process we’ve never had anything to do with before. Getting usable production parts out of our first designs was very rewarding.

Build Process Photos

Follow the Builder

• Dan Dobson: @doubled1131
• Ed’s Motorcycles: @edsmotorcycles