Five Hundred CCs of Fun

What happens when you reach the top of the tree as a restorer of classic British motorcycles? If you’re Steve Robinson you turn to building insanely fast Scomadis.

This isn’t the first of Steve’s builds to feature in Scootering. Back in March 2018, his 400cc ‘Dominator’ took pride of place on our cover. Since then he’s honed the craft of creating Scomadi transplants to a fine art, specialising in rehoming wayward GTS300 motors. Like most of us, during lockdown, Steve found himself at a loose end. He had a well-preserved 50cc Scomadi begging to be upgraded but no engine to use. “Everyone stayed at home during lockdown,” he began. “Even thieves. No GTSs were being stolen so none were being written off!” In his quest for a suitable donor scooter, Steve contacted fellow transplant enthusiast Dave Wilson of Retrotech Racing. “He didn’t have a GTS but offered me a Piaggio X9. At first I said no. I’d considered the 500cc lump before but it was simply too long to fit inside the Scomadi frame. I don’t know if it was lockdown fever or Dave cajoling me along but the more I thought about it, the more it seemed possible. No one falls in love with British bikes because they’re easy to look after. I like a challenge and if someone says ‘It can’t be done’ my instinct is to prove them wrong.”

Autos aren’t pretty but this conversion’s incredibly neat.

With the Scomadi stripped bare, Steve began to explore how the extra-long 500cc engine could be shoehorned inside the tight confines of the existing frame. “I soon worked out that if I moved the mounts forward I could fit the cylinder head under a modified bridge piece, but that caused problems with the rear suspension. Unfortunately the frame mounts were now directly above the engine’s mounting point creating a near-vertical shock absorber. In order to make the suspension work properly I had to move the frame mounts slightly.”

Article continues below...

Enjoy more Scootering reading in the monthly magazine.
Click here to subscribe & save.
Bridge piece hides the head.

At this point it’s worth reflecting on how neatly Steve carries out his work. It’s relatively easy to cut a frame and not too difficult to keep things straight. The art is in making the finished product look neat and this frame looks like something that could be used in the factory as a template for quality control. Once everything had been dry assembled Steve sent the frame and forks away for powder coating. According to him the challenge of a transplant isn’t in the engineering, it’s sorting out the electronics. “The problem is that modern motorcycles have a ‘brain’. The frame doesn’t recognise the engine and vice versa. A Scomadi is very tight in the headset so it makes sense to leave that wiring in place and splice the two looms together. I’m obsessed with neatness so the logical place to do this is in the toolbox. Unfortunately the engine’s loom is designed to fit a specific frame shape and rarely does the logical splice point match with the best location on the Scomadi, it certainly didn’t with the X9.”

You don’t have to be mad to ride this, but it helps.

Unlike classic scooters, where it’s possible to follow a single coloured wire through the loom with relative ease, the loom of a modern auto is more akin to alien technology. “A wire may start off as red in the headset, go to a relay where it emerges as two different coloured wires which in turn link into a junction box and change colour again. It’s hard enough troubleshooting when everything’s in its original frame, when a transplant’s involved it becomes a very time-consuming process. I can wire a GTS motor in fairly quickly now but the X9 was a different matter entirely. The only way I know how to do it is one wire at a time. Test it, cut it, connect it and see what does or doesn’t work. It takes forever but slowly a viable loom appears and eventually a running scooter.”

Having dismissed the transplant as impossible for so long, Steve’s managed to keep things fairly original. The paint is still as Scomadi intended but with graphics added by Dave Wilson’s son, Tom. The bridge piece is a one-off item but still looks natural, something that few auto conversions manage to achieve. Up front a Retrotech disc that’s been mated to a Piaggio caliper provides much-needed stopping power while a larger water pump swirls the required cooling more efficiently around the system. At the rear the loop’s as it left the factory and only the silencer needed any modification to fit. “It’s 75% original,” said Steve, “but don’t ask me what the end can’s from, I’ve no idea!”

Article continues below...
Scomadi blue cries out for Gulf paint.

As can be imagined, putting a 500cc engine into a frame designed for a restricted 50cc motor produces an incredible power-to-weight ratio. For that reason the X9’s motor remains in factory fitted condition, the only change being a remap to lean things out a little. There is of course one final question: what’s it like to ride? Before answering Steve pauses, laughs and then admits: “It’s scarily fast, we powered it down on the dyno at 95mph but it was still climbing. I really need to find it a home with someone who can exploit its potential.” That person has yet to emerge but when they do one thing’s for certain, 500ccs of fun await.

Transplant surgeon

Here’s one Steve made earlier …. (credit Gary Chapman)

With around half a dozen conversions out there, Steve is one of the UK’s most prolific auto transplanters but there’s no hint in his background that this would be the case. A joiner by trade, Steve’s obsession with motorcycles began at an early age when he was given a BSA C15. “It came with the condition that I had to fix its clutch on my own. My first weekend of motorcycle ownership found me buying a workshop manual and a set of clutch plates.” Never content with simply riding motorcycles, Steve was continually tinkering around and modifying them.

When he first saw the 300cc Scomadis his interest was piqued. “It was a great design but I couldn’t understand why they’d changed the engine bushes. I thought it would be better to use the originals and so I built one to see how that worked. From there I transplanted a couple of Lambrettas with GTS motors but much as I like working on the Scomadi my heart’s still with British bikes. Like classic scooters they’re always setting owners a fresh challenge!”

Article continues below...

Words and images: Stan

Subscribe to Scootering Magazine

Enjoy more Scootering reading in the monthly magazine. Click here to subscribe.

Scooter Trader