CLASSIC/HYBRID
ACCORDING TO JIM, THE OWNER AND BUILDER OF THIS HYBRID 350/650 TRIUMPH, IT ALL STARTED AT THE TRIP OUT IN 2019 – THE LAST TRIP OUT BEFORE THE WORLD WENT PANDEMIC MAD. A NICE CHAP CALLED MARK, HE SAYS, WAS SELLING A RARE 3T (NOT 3TA) ROLLING CHASSIS, WITH A V5, AND HE ABSOLUTELY FELL IN LOVE WITH IT, BUT KIND O’ HOPED SOMEONE ELSE’D BUY IT SO HE WOULDN’T HAVE TO…
The conversation turned to putting a different engine in it – not an easy task as 3T frames’re smaller than all the other Triumph rigids, and really only fit the oddball 350 engine they came with. 3Ts were the little brothers (sisters?) of the famous Edward Turner-designed 5T, you see, and were made from 1945 to 1951, with rigid frames as standard (3TAs were made from 1959 to 1966, and were twin-shockers).
They also had, apparently, legendarily appalling brakes, but that doesn’t really concern us here so we’ll ignore that fact and move on, shall we? A few brave souls over the years’ve managed to shoehorn 500s into modified 3T frames, and used them as trials bikes, and Mark knew someone near Birmingham who had a jig and engine plates to make a bigger lump work, so the die was cast – Jim’d buy it and build a special.
As I said, other people’d done 500s, but he found a rare pre-unit 650 Bonnie (only made for three years or so) engine, in bits, for sale and that gave him an idea. Given that the general consensus was that the 3T frame’s too lightweight, and small, to take any more powerful engine safely, the idea of putting the biggest and most powerful pre-unit engine into it meant that there were going to be, how shall we say this, various challenges inherent in the conversion...
The first was that, as you can probably imagine, the 650cc engine barely fits the 350cc frame; there’s about a three-millimetre gap between the rocker boxes and the frame with it in. Secondly, the frame’s not designed to take the power (3Ts made 19bhp, Bonnies make 50), so it’d need much stronger engine mounts (the new ones’re more than twice the thickness of the old, and there’s a huge clamp-on head-steady too, to tie it all together). Thirdly, the primary needed a bit of thinking about as there’s only enough room to use the 3T primary with the Bonnie engine and a rigid Triumph gearbox, but it needed to be modified to fit the bigger bearing cases, and there isn’t enough room to house an alternator or a standard Triumph clutch (it has one that’s a mixture of stuff – a four-spring affair with the centre hub machined down, two plates removed, in order to make it narrow enough, and heavier clutch springs). He also had to make a spacer to move out the outer primary cover to make space, too – “Quite a fiddle to make work,” he says. As there’s now no alternator, there’s no easy (or attractive) way to have a charging system, so it runs LED lights that’re powered off a USB rechargeable pack that lives inside the old rubber batterybox, and gives around fifteen hours of lights. Also, due to the frame being effectively shortened as part of the modifications, no standard Triumph tank’ll fit anymore so he had to cut, stretch and retunnel a Bantam tank to fit. These challenges, and many others, were all, eventually, worked around, and it now all looks so ‘right’ that most people just see a nice old Triumph, not a custom, even though, if you look closely, you’ll see it has ‘3T120’ stamped on various parts as a sign that all is not what it seems. Jim says: “You have to be a bit of a Triumph anorak to get it,” but even then they still don’t always – several Triumph anoraks, he says, have told him that what he’s done is a physical impossibility...
To ride, he says, it’s a bit of a handful as it’s so short and light. In theory it’s capable of comfortably over the ton, although he has, understandably, not really tested that, and it handles okay (“given that old Triumph frames weren’t renowned for it”). He put more miles on it last summer than he expected to, and’s only had issues with an oil leak (when the head needed retorquing), and the magneto playing up. He says he can see himself hanging on to it longterm as he’d always wanted a Triumph bobber... “Rigid Triumph bobbers from the Forties and Fifties’re just what a ‘proper bike’ looks like. I guess, like many children of the Eighties, I must have deep-seated Fonz ambitions…”