Bryan Thomas: The Wizard of Feilding

Rider Profile

Bryan Thomas and the Doug Hele-designed 500cc Desmo Manx motor in its final form with twin carburetors.

Story: Jim Scaysbrook • Photos: Thomas collection and Jim Scaysbrook

If Bryan Thomas had not been such a brilliant engineer, he could have made a living playing character roles in film and television. Neat and dapper, with perfectly trimmed moustache, Bryan is softly spoken, avuncular chap with a totally engrossing personality and a mind that never sleeps.

At 16 years of age, Bryan began not one but two apprenticeships; in Precision Engineering and Automotive (Reconditioning) Engineering. He also bought his first motorcycle at the same time.

His list of achievements in motorcycle engineering cover not just a magnitude of engines and complete bikes, but also much of the machinery needed to create these masterpieces.

Thomas 3-valve 125cc desmo.

His home in Feilding, New Zealand, sits high on a hill, with a distant view of the Manfield Circuit, and its accompanying cacophony of track noise. Downstairs is a comprehensive workshop, typically neat and orderly, with examples of his handiwork here, there and everywhere. In a separate room is a sort of mini museum, and the first thing that strikes your eye is a miniature pipe organ, which Bryan built for neighbourhood shows and charity functions. It is a real talking point wherever it appears in public and a favourite amongst the kids. In fact, there is not a square inch of Bryan’s domain that does not contain some device or gadget invented by him for some specific purpose or other. There are machines everywhere; flow-testers, dynos, machines to measure things, machines to make things or check things, and every one has its own fascinating, and often highly-technical story. Herein lies the difficulty in putting Bryan’s story to paper, for his mind refuses to accept the norm and is always striving for a better solution; a more beneficial way to do things for greater efficiency and performance. 

Crankshaft for works outside-flywheel Manx.

An example is the device he and his son Garth, a senior Project Manager with Ford NZ and a highly-gifted engineer in his own right, invented to test the idea of variable valve timing. This is something that, with today’s computers, is not that difficult to achieve, but Bryan and Garth did it the mechanical way, using nothing more sophisticated that ordinary engine oil as the modus-operandi. “We used oil because oil doesn’t hydraulic” explained Garth. “We made up a little mock where we could vary the oil in and out, so the lift and duration of the valve is determined by how much you turn the oil on or how much you allow to leak. We did it mainly to test fuel efficiency and economy, so you could button off on lifts – why have it (the valve) open a lot when you don’t need it? We found we could have it lifting just a few thou, or fully, or anywhere in between.” There are many examples of the collaboration between father and son, another being a flow testing machine. Garth did all the required calculations, then Bryan turned it into metal.

Thomas-built 350 cc desmo Manx.
The Thomas 7/8 scale 250cc Manx Norton.

Sharing the room with the Pipe organ is a row of Manx Norton engines, all built from scratch by Bryan. All incorporate desmodromic valve operation, and the crowning glory is the 96mm bore x 69mm stroke engine designed by Doug Hele to be the ultimate incarnation of the Manx design. Inside the head are four titanium valves, set at an inclined angle of 22 degrees. Dual inlet ports carry two Amal GP carburettors, one smaller than the other and opening earlier to produce what is termed a Lagging Throttle System. Ignition is by battery and coil firing two spark plugs. “It’s not finished,” says Bryan a touch whimsically,” and it will never be. Doug Hele is now deceased. He never got around to actually making the engine but talked I talked to him numerous times before he died about six years ago and told him what I was doing and he said, yes, that’s what I would have done.” Bryan is justifiably proud of the intricate wooden pattern boxes for the tricky-to-cast Manx heads. The patterns for each fin can be individually lifted out without the same breaking.

Patterns for Villa V-twin two stroke crankcases.

Alongside, mounted on their own stands are two more Manx engines, using Bryan’s own desmodromic system. One uses the Hele 96 x 69 dimensions, the other a massively over square 103 x 60. Both have three desmo gears with two opening rockers and two closing rockers, with each cam individually balanced. The two valves are set at a very narrow angle and offset to the centre-line of the head, producing a larger squish area.

Balance is something that Bryan holds paramount, and naturally, he has made his own dynamic balancer. “We can put a crank on the balancer, less the conrod – we add a weight of the rod – and a belt runs across the top of the flywheel and all measurements are shown on the oscilloscopes. We can balance the unit at every point in the rev range. Our 350 engines are so smooth that you can practically balance a coin on its edge when running. We don’t go near static balancing – that’s out!”

Sitting amongst the Manx engines is what looks like half a Ducati engine, and that’s not far from the truth. “This is the second 250 engine I built,” explains Bryan. “It has a 750 Ducati head and barrel, wet sump like the Ducati, outside flywheel, one-piece crank.” Indeed, 250’s are what seem to really take Bryan’s fancy, and that leads us to the machine for which he is probably most famous – the 7/8 scale desmodromic 250 Manx Norton.

The second 250cc engine built by Thomas, using a 750cc Ducati head and barrel.

“I was the first person to make a 250cc 7R AJS. That was many years ago and the motor went to Sydney. When I decided to make the 250 Manx in 1995 I thought that whatever we did with the engine would be wasted in a standard Manx Chassis – far too heavy, so we made our own in 7/8 scale – everything is this scale except the gearbox and the carburettor. In fact I made three at once, the first was a valve spring motor and the other two were desmos, using the Hele arrangement of five gears across the top, with the intermediate one having the closing cam on it. We took the 250 to Assen in 1998 and Rod Coleman rode it. Rod bought the bike but subsequently sold it to Ferry Brouwer who organised the Assen meeting. We spent a lot of time on the flow bench (another machine Bryan and Garth have constructed) getting the best combination of squish and flame travel and it really works well. If you can’t measure something, you’re just guessing! Rod Coleman couldn’t believe how fast it was. The 250 has a 70 x 64 bore and stroke, 11:1 compression ration and develops maximum horsepower at 10,000 rpm.”

The DOHC 250cc Ducati head.

Sitting alongside Bryan’s desmo 350 Manx graphically illustrates how petite the 250 really is. “The 350 is a completely different design, my own ideas. It has a more vertical valve angle and has 5 gears across the top. Like the Hele engine, we have done away with the magneto and use a coil ignition and points.”

Another very handsome creation is the 3-valve DOHC desmo 125 built in 1987. “I was going to make the whole thing but in the end the top half was grafted onto a Honda 125, 6 speed crankcase. We built a smaller water-brake dyno especially to test it and it runs happily to 12,000 rpm but will go to 14,500.” The Thomas DOHC, as it is officially known, has a 56 x 49 bore and stroke with 10:1 compression and develops 19 horsepower. 

Thomas-built DOHC 250cc Ducati.

Decked out in rather garish hues of yellow cycle parts with copper-toned engine is Bryan’s DOHC 250cc Ducati – converted from the original SOHC design and bristling with typical original thinking. To allow for ease of setting valve clearances without disruption of the cam gear assembly, Bryan devised a split-casing design and squeezed a second spark plug into the head.

Then there’s the 175cc version of the 250 NSU Sportsmax. Right down to the hand-beaten alloy fuel tank, the NSU is perfectly proportioned, but in miniature. “It has to be”, explains Bryan.” Our (NZ) racing rules permit internal modifications providing the original external appearance is maintained. Appearance, note, not dimensions.”

Miniature 175cc version of the 250cc NSDU Sportmax.

What’s next? Well, in one corner of the workshop sits the chassis for the 250cc V-twin Moto Villa 2 stroke GP racer, as well as patterns for the engine. “When we went to Assen in 1998, the Villa brothers were parked next to us in the pits, and became interested in their work,” says Bryan. “I also want to make an ultra short stroke Aermacchi, and I have all the patterns for a 4-cylinder Gilera stored under the house, but it’s not a 500, it’s a 250.” Of course it is.

At many New Zealand classic race meetings, notably the Pukekohe Classic Festival, the Thomas family set up their display and it is interesting to note the way the bikes stop onlookers in their tracks. You can almost read their minds as they stare at the miniature machines thinking, “I must be getting old. I’d swear those bikes were bigger than that!” Throughout the three days of the Festival, Bryan and Garth happily chat, fielding questions that range from the well-educated to the naïve. And around the paddock, a goodly number of the competing machines have received the Thomas touch, either directly or via the technology developed in the fascinating workshop at Feilding. 

This article first appeared in Old Bike Australasia Issue No.11