Fashions change and times move on, and Pre-65 machines are no exception. In the early days the Sammy Miller Ariel 500cc replica was the ‘bees knees’, and this trend evolved through the lighter machines such as the four-stroke BSA C15/B40 and Tiger Cub, th
Choosing your Pre-65 mount is a delicate choice, as there are so many options to create a highly competitive machine using the myriad aftermarket parts that are available. Once you have decided on the format: four-stroke, two-stroke, large or small capacity engine, single or twin cylinder, then the fun begins in creating your ideal ride. If you hanker after a twin-cylinder engine then the choice seems to be quite limited.
A Triumph Twin is by far the most popular choice, although I have ridden an Ariel Arrow and the Lejeune Honda twins. The Triumph has been popularised in recent years by Steve Saunders, who used one to win the 2011 Scottish Pre-65 event, followed up by Rob Bowyer in 2014. Although if you look back through trials history there were not many riders of the time, with the exception of Johnny Giles and Roy Peplow, who ever won major
events on these machines. So what has changed in the fortunes of the Triumph Twin? For most, I guess, the path starts when they hear one in action. The rorty, rasping sound of the twin on full song is unlike most other you are likely to experience at a Pre-65 trial. This is the major reason owner Mark Stokes chose to build the test machine. He also wanted one that was eligible to ride in the Scottish Pre-65 event, and rode to a Special First Class award in 2014. So I was sure the test machine was fully sorted.
Royal Enfield Chassis
This machine, like Steve Saunders’ version, has the engine built into a Royal Enfield Crusader frame which, unlike the Triumph version, is all welded as opposed to the ‘lugged’ original and gives a significant advantage in terms of weight and more importantly wheelbase, as the swinging arm can be tucked much closer to the rear of the crankcases than on the Triumph, whose mounting point is a large cast lug behind the gearbox. The wheelbase is currently 52½ inches, which is similar to a modern machine, and very reasonable nevertheless.
Mark poured over many photos of the Sanders machine and fitted the engine in exactly the same place. This necessitated cutting the swing arm mounting brackets and re-welding them in such a position that when the rear suspension travel is half used there is a straight line between the gearbox output sprocket, the swing arm mounting point and the rear wheel spindle. Custom alloy plates locate the front of the engine and a substantial head steady connects to the top frame tube.
Once the engine is fixed then the ancillary parts need fitting or fabricating from scratch. Starting at the front end a set of alloy yokes from a well known internet auction site was fitted. These mount the handlebars slightly in front of the steering step and are fitted with Renthal handlebars and Domino levers, and a fast-action throttle. The forks are Royal Enfield lowers with a slight leading axle and the internals are by Betor from an Ossa Gripper. To ensure Scottish eligibility the wheels are fitted with replica Tiger Cub hubs supplied by Alan Whitton Race Engineering, laced with stainless spokes to a black SMPro Platinum rim, which I think adds a classy modern twist to the look! Rear suspension is taken care of by some custom-built black anodised and subtly engraved Rockshocks suspension units. The petrol and oil tanks are custom built, and they hold sufficient fuel and oil for most events. As Triumphs are renowned for running hot, a trick oil cooler from a Honda XR400 model tucks neatly around the steering stem, feeding cooler
oil to the rockers. The exhausts are high level, made by Dave Tyler, and are ceramic coated inside and out to reduce the temperature. They exit into a tiny alloy silencer just under the seat, which was fabricated by Chris at Silverback Engineering. Surprisingly for such a small item the machine is acceptably quiet and the silencer does not restrict the engine performance at high revs.
For the rest it is worth noting the substantial sump guard, which is double thickness under the vulnerable lower section. A Sherco alloy side stand and a modern chain tensioner with an alloy rear mudguard mounted on short brackets finish the good looks.
The more you look round the machine the more you see the attention to detail is exceptional. All the fasteners are very ‘trick’, with lots of gold anodised alloy spacers to give a smooth uncluttered look.
The engine is much more standard but it is the small hidden details that make the difference. It has been under development for a couple of years to iron out the inevitable issues of converting a road motorcycle engine for trials use. For a start it is the full 500cc power plant as opposed to the more commonly used 350cc unit construction motor. The pistons are the low compression 7:1 type by Triumph. The camshaft is also the ‘cooking’ road version and the pushrods act upon a smaller 350cc (15/16”) inlet valve combined with the large 500cc exhaust valve. This solution took some time to arrive at and Mark thinks it is the biggest single improvement he has made to cure the ‘cough’ that sometimes plagues four-stroke engines at low rpm.
Another improvement was the use of Champion N12YC spark plugs. As there is no visible distributor or points housing this can mean only one thing: electronic ignition; in this case it comes courtesy of Electrex. The carburettor is an Amal concentric 22mm using the following jetting: Main 180, pilot 106, needle 2, slide 3. The clutch is standard Triumph issue and uses a standard-tooth duplex engine sprocket. The gear box is a special low ratio unit, with first and second gears being close together meaning that you have a choice. However, Mark normally uses first gear for most sections. The final sprocket ratios are a 15 tooth gearbox and an extra-large 54 tooth on the rear wheel; the machine is slow on the road but perhaps still not quite slow enough in sections.
Rip and Roar
I had the pleasure of riding around with Mark and Steve at the Soultz Two Day Trial so my impression on how the machine rides is based on my own time riding it, and watching closely how it reacted when being ridden by a good rider on the highest level of difficult sections. Mark’s record speaks for itself; he was a top schoolboy trials and motocross rider and then competed for many years in British Championship Enduro. In recent years he has won the highly competitive Sammy Miller Twin-Shock Championship twice, as well as the 2014 FIM Classic Trial Cup for Pre-65 machines.
Starting the machine is easy, as a slow push on the long kick-start fires the engine up quickly and once fully warmed it settles into a steady burble. The clutch lever is nice and light and the first gear snicks in with almost no sound or reaction, it is so smooth and slick I had to check it a couple of times to make sure we were in gear! First gear is quite short with revs climbing quickly; you do not get the thump, thump sound of a big single where you can count each power stroke but a much more frenetic roar of a ‘racing’ engine. The revs rise and fall quickly, making it much more modern in its feel. The riding position is also surprisingly modern, with the low mounted footrest and higher bars falling naturally to hand.
Looking down from the cockpit past the slim alloy tank reveals a fair amount of engine sticking out on each side, with the Siamese exhaust system dominating the left. This is something of an optical illusion as in reality the engine is no wider than the rear suspension units. Happily the centre of gravity seems quite low, with no sensation of falling into corners. The steering lock is excellent and the tightest of turns are feasible. It is possible to use the clutch as it feels very modern in its action, with no grab or slip, however the engine has more than sufficient torque to blast up a climb should you ride in the older style. It takes some time to recalibrate your riding style as engine braking is quite strong but also smooth. The machine decelerates nicely when you snap the throttle shut and makes up for the difficult to reach and spongy rear brake. For me this is the worst aspect of the machine as a long cross-over cable takes the left side drum to a right side footbrake. In the end I just forgot about it and used the engine.
There is one thing a 500cc trials engine on full song is not short of, and that is power; open the throttle and it sets off - and boy, what a noise! It is quite addictive and I can admit I am a convert to the experience. I did once own an immaculate Fred Hardy 350cc twin but could never bring myself to use it in anger as it was so nice.
The only thing that you need to think about in advance is the need to pop the front higher than normal and pay attention to not catching the sump guard on rocks, as the machine feels long, low and wide. You can easily lift and float round the front wheel thanks to the amazing power delivery; a period of adaptation is required but once you learn how to use this feature it makes life easier. The suspension is very compliant and works perfectly well going uphill, the Rockshocks are excellent and keep the Michelin X-Light tubeless rear tyre in contact with the ground and gripping away. I thought that the sidewall may be too flexible but in reality the modern tyre is excellent on such an old girl. The top mounting point of the rear suspension is integral with the rear frame, and as such sliding back on downhills is much easier as there is not the lump of the top mounting as found on other machines, a small detail but noticeable. On descents the front fork springs seemed too soft with such a heavy package of man and machine, and they bottomed out fairly easily. Mark confirmed the sensation and said he has fitted the heaviest rate ‘Magical’ springs available but it was still not quite enough.
So there you have it a fantastic piece of kit. There is no doubt Mark has created a superb weapon that is clearly very capable in the right hands and is much more docile than you would first imagine. The time, effort and frustration that goes into getting a special together is well rewarded when it works as well as this one. It is also clear that observers and spectators alike enjoy watching it and listening to the ripping and snarling through sections as it is a pretty unique aural experience.
My thanks go to Mark for trusting me with his ‘Special’ machine, and to Steve for manning the camera.
As Triumphs are renowned for running hot, a trick oil cooler from a Honda XR400 model tucks neatly around the steering stem, feeding cooler oil to the rockers. The Siamese exhaust system dominates the left hand side. It’s the full 500cc power plant as opposed to the more commonly used 350cc unit construction motor.
Looking down from the machine past the slim alloy fuel tank reveals a fair amount of engine sticking out on each side. This is something of an optical illusion as in reality the engine is no wider than the rear suspension units.
Rear suspension is taken care of by some custom-built black anodised, and subtly engraved, Rockshocks suspension units.
The forks are Royal Enfield lowers with a slight leading axle, and the internals are by Betor from an Ossa Gripper.
Total concentration for our ‘Test Pilot’.
The substantial sump guard plays its part.