Teenage dreams: We ride Allen Millyard's Honda SS50 specials

The humble Honda SS50 is iconic. Built and sold in their thousands as the moped craze swept through 1970s UK, the slick-looking four-stroke looked like a miniature motorcycle. Flat bars, upswept exhausts and a sexy slim tank, it was every boy racer’s dream… until, that is, they prodded the kickstart.

For all its show, the SS50 had no go, and hot-headed 16-year-olds opted for the zippier two-stroke competition when they discovered the 3bhp Honda took 19 seconds to reach 30mph (10 seconds more than Yamaha’s 5bhp FS1-E) before topping out at just 40mph while the Fizzy cruised on to 50.

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A modification to the carb helped things – slightly – but short of major surgery the little Honda just couldn’t take the pace. Massively reliable, it just wasn’t quick enough, and that really matters when you’re young.

It mattered to specials genius and childhood SS50 owner Allen Millyard so much that 40-odd years later he decided to redress the balance by building not one but two incredible Honda SSs.

Look carefully and you’ll see one of them is actually a 100cc V-twin, while the other has an over-sized 250cc single from a motocross bike skilfully slotted in. And what’s more, the 250cc makes 40bhp – that’s ten times the power of the original Honda.

“I owned an SS50 as a youngster and loved it, but it wasn’t until 1999 that I built my first SS50 V-twin,” Allen told MCN.

“I’ve been shoehorning big engines into different machines for years, but it was time the little SS50 got some attention. I did the complete build live at a motorcycle show over the course of a few days, and got it up and running on the final day. It ran perfectly.”

Although Allen makes it sound as if creating a bespoke V-twin engine is something he could do in his sleep, the level of engineering that’s gone into this most mesmerisingly mutated moped would’ve impressed Soichiro Honda himself.

“One of my overriding priorities is that it has to look as if it rolled out of the Honda factory like that, so I engineer it to suit – even down to the webs on the crankcases.

“As I had to incorporate the width of another connecting rod on the crankshaft, the engine is 15mm wider than stock. But this extra width was only built into the front of the engine, so the rear still bolts into the standard frame mounts. This makes it so much easier for everything else to line up and helps retain all of the stock chassis ancillaries.”

Single grows a cylinder

Allen starts by cutting the crankcases into quarters, and welds sections of old Honda cases together to help retain the stock appearance. “The front cylinder needed some modifying to keep the cam chain inline,” admits Allen when asked if he faced any particular challenges in splicing the engines together.

“The offset meant the camshaft and tunnel needed extending, again using Honda parts, then the rest of it was a standard build times two.”

Of course, having two cylinders instead of one means that the SS’s power output has doubled, so Allen reinforced the chassis internally to cope with the extra performance, and the result is stunning.

Riding the little V-twin can only be described as idyllic, and the perfectly balanced twin sounds like a miniature Ducati bevel motor. As it comes on cam, around 40mph in third gear, it hits a sweet spot; the tiny chassis usually maxes out at this speed with the original 50cc engine, but despite having double the power it feels settled and as you change to fourth the extra shove from the twin swiftly takes it past 50mph. It really makes you wonder why Honda never built one themselves!

Yet Millyard’s engineering madness doesn’t stop there. For years Allen had nurtured the idea of putting a 250cc single-cylinder four-stroke motocross engine in an SS50; amazingly the bigger engine is very similar in weight to the original 50cc Honda motor, however the modern 250 lump not only has the benefit of extra capacity but is also packed with magnesium and other lightweight materials.

“In an ideal world I would’ve used a Honda CRF250 motor, but you just can’t find them for sale anywhere. The only way to get hold of one was to buy a complete bike and take the engine out, but that’s a bit unrealistic and expensive.

“So a friend of mine who is a dealer mentioned that he had a Kawasaki KXF250 engine in bits, it needed rebuilding but was a bargain so I jumped at the chance. In some ways the Kawasaki engine is better, it’s twin cam and looks more pleasing to the eye.”

Strengthened on the inside

Owing to the new engine’s modern lightweight internals and design, Allen’s 250cc SS weighs much the same as it did as standard, however with 40bhp now on tap it makes ten times the original power!

“Because of all the extra power, the transplant isn’t as straightforward as simply grafting the bigger engine into the frame,” says Allen. “There are many modifications, mostly chassis related. The frame needed strengthening and all this was done internally so from the outside it looks completely standard.

“The forks have been beefed up by 2mm, there’s heavy-duty Hagon spokes in the front wheel, a drilled standard disc and a KX85 twin-piston caliper.

“I had to build the swingarm from scratch, because there wasn’t really a way of strengthening the original internally. It’s constructed from cold steel rod 3.2mm thick, and needed to be longer than standard because the extra power made the bike twitchy.

“Even things like the gearing needed a rethink; for a start the drive chain needed to be uprated from a 420 to 520 to cope with the extra power. Then the final drive sprockets needed to be made, it’s amazing how small the rear sprocket needed to be, it went from 48 teeth to a tiny 28!”

The detail of the build is true to how it would have been made if it was a factory-made production machine. The radiator and cooling system are beautifully finished, and the speedo is from a CB450 with a cleverly incorporated digital temperature gauge.

The real skill of building this bike, and the little V-twin, is the seamless and natural way all of the modifications blend in with the SS50 silhouette. Which makes riding the SS250 a real shock, albeit an unforgettable and unique one.

As soon as the big-little single fires up it feels unnatural, and you have to remind yourself that you are sitting on a tiny SS50 chassis with its super-low seat and narrow bars.

The instant response from the engine gets your attention and I remind myself that I need to take care; it’d be mortifying if I were to rev it too hard and flip it over.

It’s unbelievably fast

So it’s with an air of caution that I put it into gear and let the clutch out with an almost sedentary level of rpm… and it stalls!

“You need to slip the clutch loads!” laughs Allen, as he reminded me of the SS250’s insanely tall gearing, almost 60mph in first gear. With the feel for the gearbox and engine, I unleash the power and find the little machine is unbelievably fast.

It feels so unnatural to have a tiny chassis with so much power and you need to ride it in much the same way as a big bike; predicting how much throttle to give it flowing through fast bends, optimising the gear changes, and of course shifting your bodyweight to counter the front-end going light all the time!

Out of the two Millyard specials it’s the SS250 that really blows me away. Both bikes are built with superb attention to detail and engineered to perfection, but it’s the riding experience from the 250 that generates genuine raw excitement and speed. Simply amazing.

Honda SS100 stats

• Engine 90 Degree V-twin 98cc
• Bore & stroke 39mm x 41.4mm
• Power 10bhp
• Weight 80kg
• Gearbox 4 speed (70mph @ 10,500rpm)
• Forks Std with heavier springs
• Ignition Points and coil
• Front brake Drum
• Rear brake Drum
• Electrics 12 volt

Honda SS250 stats

• Engine 249cc single-cylinder from 2005 Kawasaki KXF250, with handmade stainless steel exhaust
• Bore & stroke 77mm x 53.6mm
• Power 40bhp
• Weight 85Kg
• Gearbox 6 speed, 520 chain sprocket size F14T x R 28T (110mph@ 11000rpm)
• Front brake Hydraulic twin piston calliper, drilled disc
• Rear brake Drum
• Forks 27mm stanchions and upgraded damper, heavy duty springs
• Extras 12v ignition, LED lights Kosso Electronic rev counter Digital temp gauge incorporated into Honda 110mph Speedo

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Who is Allen Millyard?

Allen builds these incredible specials at home in his single garage near Thatcham, and it’s a hobby he’s had since he was a youngster.

“The first bike I modified was an old BSA Bantam, I was 15 at the time and managed to fit an old Austin 850 Mini engine into it, by cutting the frame in half and then fabricating it all back together. I rode it to school to show my metalwork teacher, he was really impressed,” remembers Allen.

“My first show-winning bike wasn’t really planned; I was given a KH250 as part-payment for a job I did. I intended to restore the bike so stripped it all down and noticed how much work it needed.

“It would have cost a fortune to do, so I lost interest in restoring it nicely. But when I stripped the engine down I noticed how the Kawasaki engineers had modified the A7 Avenger 250 twin engine into the triple. So all I did was copy what they had done in the same way, but adding another two cylinders.

“So that was the first one I made and it won loads of shows. I couldn’t stop by then and I took my absolutely mint KH500 triple, cut up the motor and made that into a five cylinder as well, and again won some prestigious shows.”

As well as the Kawasaki triple Allen has transformed a Z1300 from an inline water-cooled six cylinder to a V12, a Kawasaki Z1000 in-line four into a V8, the huge Flying Millyard and also made a bike from an eight-litre, V10 Dodge Viper engine which he rides most days!

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Shed Zed packs a bigger head: Kawasaki Z1 Super Six from Allen Millyard

First published on May 19 by Ben Clarke

Shed-based engineering hero, Allen Millyard is putting the finishing touches to his latest project, a pair of six-cylinder Kawasaki Z1s that he’s built by hand at home. Despite the fact that the bikes look every inch like long-lost Kawasaki prototypes, they were imagined by Allen and put together using parts from original 1974 Z1s. Sounds simple doesn’t it?

“Everything is a problem when you’re converting a four-cylinder crankshaft into a six-cylinder,” Millyard told MCN. “All the balance weights were in the wrong places, so I had to re-engineer those.

“Then when I cut the crank cases all the studs were in the wrong place so I couldn’t just hang a cylinder on either end like I wanted to, although that’s sort of what I did do. I always run into problems; I just don’t dwell on them. I sort them and push through them.”

The extra cylinders are actually added in the middle of the new engine. A first engine is cut in half straight down the centre and then cylinders two and three are cut out of the second. These are put into the first to become cylinders three and four of the finished six-cylinder motor.

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Astonishingly, Allen doesn’t write things down or design anything on paper. “You have to three-dimensionally visualise the whole thing in one go and then fix all the problems at the same time.”

And Allen’s imagination is obviously a very powerful place, as the first engine went from an idea to running in just six weeks. “The second one is significantly easier than the first. Whereas I had to dwell on something for a week the first time round I can just go straight through that process.”

“I’ve bought damaged engines and corroded engines of the correct year and refurbished them to make them look new, I tend to use the 70s stuff because it’s better. I wanted to keep it as original looking as possible so that from the side, you can’t tell it’s modified. So many people online think it’s a genuine bike and that’s properly cool when that happens.”

Overall, the first bike took just 13 weeks to build using a restored Kawasaki Z1 900 and parts from two 890cc Z1 engines, giving a new capacity of 1355cc. The second bike will take longer to finish because Allen is taking his time with it but it uses the slightly larger 1015cc sleeves from a later Z1 engine giving a new capacity of 1522cc.

“It has got an electronic ignition, that’s the only upgrade I do fit. The original would have had points and coil and condensers and things but Boyer Bransden made me a really cool ignition system for it but that’s the only ‘modern’ thing I’ve got on there.”

You might assume that figuring out a new firing order and crank arrangement would be a challenge when moving from four to six cylinders. “That’s easy,” explains Allen, “I use a 120-degree crank so the middle cylinders are offset by 120, then the next two and then the outermost two. So you end up with a standard firing order.”

Allen has to work out what that firing order is (1-4-2-6-3-5) for me because he says, “in my mind, it’s not a significant thing to worry about.”