World’s Smallest V-Twin Motorcycle: Honda “SS100”

99cc Honda SS50 V-Twin from Allen Millyard… 

Introduced in 1967, the Honda SS50 was a schoolboy’s dream. The 49cc OHC four-stroke featured a long race-style tank, gorgeous heat-shielded high-line exhaust, and even a café-style bum stop seat on some models. While it wasn’t as quick as some of its two-stroke rivals, it was more reliable and economical, returning over 120 mpg!

The SS50 was even available with pedals to classify as a moped, as certain countries and states allowed riders as young as 14 to operate “motorized bicycles” on the street. The pedals could be rotated forward to serve as a regular footrests, so they didn’t mar the bike’s boy racer image too much. Over time, the SS50 gained a 5-speed transmission, front disc brake, a larger engine, and even electric start.

However, the lack of umph remained a drawback. With just 4.2 bhp available from the 5-speed model, the SS50 was no race bike, and young riders often found themselves left in the blue smoke of two-strokers like the Suzuki AP50 and Yamaha FS1E Fizzy.

That’s where Allen Millyard comes in. The English shed-builder has become a living legend, renowned the world over for building massive multi-cylinder engines with little more than a lathe and hacksaw. Examples include his Kawasaki Z1 V8, Kawasaki Z1 Super Six, Viper V10 bike, and his 5000cc V-twin Flying Millyard.

5000cc V-Twin! “The Flying Millyard”

While Millyard is best-known for going big, he also goes small. In fact, he’s built the world’s smallest V-twin from a pair of Honda SS50 engines.

“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 Millyard, MCN

Not only did a Millyard build a 99cc V-twin and put it in a reinforced SS50 chassis, he built it live at a motorcycle show over the course of just a few days, firing it up for the first time in front of slack-jawed onlookers. The tiny V-twin sounds amazing, almost like a miniature Ducati twin.

He’s now built a handful of these tiny V-twins. When it comes to the crankcase, Millyard always wants it to look as stock as possible. He starts by cutting the cases into quarters and welding in new sections, shaping them with rotary burrs, and sanding / filing them down smooth to blend with the existing crankcase finish.

The front cylinder has to be offset slightly to keep the cam chain inline, which requires extending the camshaft and tunnel. In order to fit a second conrod to the crank, Millyard has to make the engine 15 mm wider than stock, but all of the extra width is at the front of the engine — the rear still bolts to the standard frame mounts.

The pressed-steel frame of a 1974 SS50 was modified and reinforced to hold the V-twin, with all welds ground down with an angle grinder and fine-grit flapper wheel. The bike runs a high-performance four-plate pitbike clutch instead of the standard two-plate unit, which wouldn’t be able to handle the additional power. 

So how horsepower does the diminutive twin make? Allen got his first Honda “SS100” V-twin on the dyno, where it put down 10.5 horsepower at 11,000 rpm — more than double the original, which Millyard attributes to larger carbs and a free-flowing exhaust.

“It’s so light and flickable through the bends, holds 60 mph on the flat and will return almost 100 mpg.”

The bike won the “Biggest Wow Factor” award at London’s prestigious Salon Privé Concours. That’s also where he got the idea to build his 5.0L V-twin.

“I thought, if I’ve won this year with the world ‘s smallest V-twin, I’ll come back next year with the world’s biggest!” -Millyard via MCN

He rode his original SS100 about 3000 miles before selling it to the Barber Museum, where it’s housed among his Kawasaki Z1 V8 and Z2300 V12. Millyard has built four SS100 V-twins — we’re sure Soichiro Honda himself would’ve gotten a kick out of these tiny wonders!

Millyard SS100 Videos

Here’s a 7-video playlist that Millyard put together about his SS100 and SS180 V-twins. Enjoy!

Follow the Builder

Instagram: @allenmillyard
YouTube: @AllenMillyard

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