Memorable MC: Hans Van Bregt Minarelli 50

March 26, 2015
Frank Melling
Frank Melling
Contributing Editor| Articles|RSS Our Memorable Motorcycles expert, Frank Melling also is the organizer of the British vintage motorcycle extravaganza known as Thundersprint. Melling began riding five decades ago and remains as much in love with motorcycles as when he drove his first bike into a cow shed wall aged ten. In the last 50 years, Melling has competed in every form of motorcycle sport and now declares himself to be too old to grow up and be sensible.
Hans Van Bregt Minarelli 50 – the 120mph Moped Writing for MotoUSA really is a brilliant job and I would recommend it wholeheartedly to any aspiring writer. It’s not so much a 9-5 occupation but rather a 60 seconds a minute, 24/7 lifestyle – and one of the best things is that you never know where the next story is coming from.

Let me set the scene. Carol and I are having a weekend away from work so what else would we do but find a vintage meeting where we can run our Seeley Suzuki? In this case, it’s the wonderful “Pistons and Props” revival festival which sees classic bikes run demo laps alongside vintage drag racing cars while World War II Spitfires and Hurricanes strut their stuff overhead. Now, how good is that?

Carol is a gourmet paddock cook so we’re sat in the soft, warm, autumn sun enjoying a relaxing lunch, and who should walk past but one of the world’s greatest authorities on classic racing 50cc bikes, Dutchman Hans Van Bregt. Hans is a lovely bloke and we get on very well. He makes his normal jokes about 500cc race bikes being too fat and heavy to be fun and then says: “If you want to see how a classic race bike can really perform, you ought to ride a 50!”

There’s no argument about the skill of 50cc pilots riding bikes with tires the size of a mountain bike and engines with a useable powerband of 3rpm. The problem is that I was never fond of mopeds even when I was riding them illegally as a 10 year old, so I answer yes, well, maybe, very interesting but we’ve got a lot of bikes in the schedule – and then pick up another sandwich and top up the Greek olives and Cheshire cheese on my plate.

But Hans is having nothing to do with my reluctance. He says: “I’ve got my bike here now. Get your leathers on and you can ride it in 20 minutes.

“If you can ride it…”

Of course, the last comment is the ignition switch on NASA’s next rocket launch to Mars. I have ridden everything from the eight cylinder, Moto Guzzi GP bike to the soul destroying, but still fascinating, Honda DN 01 so I am certain that I can drone round Sywell at 30mph on a tuned moped.

Ten minutes later, Hans introduces me to the bike I will be riding – and it’s immediately time for a radical re-think. For certain, this is no moped with a nice paint job but rather a full on, serious race bike – just one which has shrunk to miniature proportions.

The double sided  twin leading shoe brake is enormous by 50cc standards.
The double sided, twin leading shoe brake is enormous by 50cc standards.

Starting at the front, there is a beautiful, double sided, 110mm (4.3-inch), Ceriani, twin leading shoe front brake which would stop a 125. Hans explained: “You can make up a lot of time with that brake which is really more for a much bigger bike. There are only two throttle positions on a 50 – completely flat out and totally closed.

“The power of the brake allows me to go very deep into a corner, still using full power, then sit up from behind the fairing, brake very hard, and then get the power on again and tuck in.”

The Ceriani front forks are just as race focused and, again, look as if they could handle a 125cc engine.

The frame is an exact replica of the 1971 Minarelli works design but now built by the Italian PCB company. It is of a full, duplex design and, with its 1260mm (49.6-inch) wheelbase it’s roomy inside – for a 50 at least. Note the caveat – “For a 50!”

Front to back, there is sufficient room to just about squash my 5’ 10 .5” body into the available space – it is both the width, or lack of it, and the footrest to saddle distance which are the problems.

To be quick on a 50, the rider has to be completely behind the fairing – literally with not a single inch of his body stuck out into the air. This means it is essential to have your knees inside the fairing. Since the Minarelli is about the width of a gnat’s eyelash, the only way to get everything tucked in is to squash your legs tight.

However this Las Vegas contortionist act is not as straightforward as it seems. Because the footrests are so high, and the saddle is so low, the riding position requires the rider to lie horizontal on the bike.

The Minarelli 50 is wafer thin.
The Minarelli 50 is wafer thin.

For me, there are two problems. First, my belly isn’t what it was when I was 20 years old. For some reason, it seems to have expanded – I can’t think why! This means that four decades of good food have to be jammed into a space where they would never, normally, be expected to fit.

Along with the expanded waistline is a lifetime of racing injuries, including numerous major knee incidents. Now, my knees are completely shot and so take extreme exception to being bent so tightly in order to reach the footrests.

I don’t want to go into the final problem in too much detail but here’s a summary. Since I am too tall to fit into the available space my feet push a certain part of my anatomy into the back of the fuel tank. This delicate area gets very, very, very severely flattened. I’ll leave you to fill in the details…

The chassis of the Minarelli is very interesting but the magic lies in the engine. At first glance, it is deceptively simple but I want to work backwards from the key figure. This tiny 40 x 39.2mm engine produces an astonishing 22 horsepower and equally amazing 9.4 lb-ft of torque.

The maximum power figure needs to be put into perspective. The best MotoGP engines produce around 250hp/liter compared with Hans’ home tuned Minarelli’s 440hp/liter. No normally aspirated engine in the world, running on freely available gasoline, can get near Hans’ garage engineering. No other word except genius can describe him.

The power comes from a mixture of art, engineering craft skills and technology. The water-cooled, single-cylinder Minarelli engine looks deceptively simple being fed through a disc valve by one huge 28mm carburetor. Where the carburetor finishes and the engine starts is the point at which things get very clever.

First, the fuel is fed into the engine via a disc valve. This is a circular piece of metal with a section cut out. When the open section passes a hole in the crankcase, the fuel enters the engine and the combustion cycle can begin. Except, of course, it isn’t this easy. The precise size and shape of the cutaway has an immense effect on how much power the engine makes and so Hans’ discs are a more closely guarded secret than the US gold reserves at Fort Knox.

When the charge is inside the crankcase, it is forced up into the cylinder through a series of equally secret ports which allow the motor not only to make incredible power but an equally astonishing level of torque. In practice, the 50cc Minarelli will pull better than a good 125cc race engine.

Finally, a handmade exhaust exploits the Kaadency Effect – the phenomenon developed by the father of the modern racing two-stroke, MZ’s Walther Kaaden. This genius discovered that by making a single molecule of gas from a two-stroke first expand in the exhaust and then contract, a sound pulse could be created which would effectively suck the burnt charge from the cylinder. In doing so, fuel consumption was decreased and both maximum power and torque were increased enormously.

On Hans’ bike, the exhausts are hand-made, using old fashioned crafts skills, by Kees Van Dongen – and that’s not a skill you get with a downloadable app!

The problem with all this engineering is that it requires supreme precision – and yet this is its strength too. The German and Dutch engineers Jörg Müller and Jan Thiel were heavily involved in the Kriedler 50cc GP racing team which was based in Holland. Together with Kriedler and later Morbidelli, between them they won 21 World Championships with lightweight racing two-strokes. It is their legacy which Hans has built into his Minarelli.

Now, Hans has access to modern Minarelli scooter cylinders which are Nikasil plated and have a much more accurate cylinder bore to piston clearance than the old GP engines.

Add all this knowledge, heritage, engineering skill and science together and you get 440hp per liter.

There is an interesting footnote to the magic. Electronics have progressed immensely in the last 40 years so one might reasonably think that Hans would have the very latest ignition unit on the Minarelli because ultra-accurate precision timing is life and death in terms of getting a two-stroke to make power and stay in one piece. However, Hans uses an original Philips design from the late 1960s which he says is the equal of anything available today.

If I thought that the bike was tiny as I sat on it in the paddock, wearing jeans and a T-shirt, that was nothing compared to getting me, my back protector, knee sliders and bum into place as Hans pushed me off the start line!

Starting the Minarelli is simple. The rider sits on the bike, paddles it for a few inches and half drops the clutch. The tiny piston zips up and down and the engine fires. On a normal racing 50, here’s where the pain begins because the motor normally refuses to run at less than a zillion rpm.

Hans’ bike couldn’t be more different. It fired up instantly and pulled away in a manner which was quite astonishing. In fact, I have ridden 250s which were peakier.

Once above 11,000 rpm, the tiny motor was perfectly rideable and when we hit 16,000 rpm it was so much faster than the other 50s that it was embarrassing. Sywell uses an airport runway for its main straight and it was only for fear of blowing up the motor that I rolled it off. Up to that point, the Minarelli simply disappeared. Hans reckons on a top speed edging towards 120 mph and the way the scenery blurred past I’m certain that, even with a big, fat lump like me in the saddle, we zipped through the 100 mph barrier.

The engine felt wonderfully sweet and full of willingness to race. Hans told me to change on the engine note because he feels that a rev counter is an unnecessary distraction. Living with the Minarelli race after race, Hans knows instinctively just when the motor reaches peak power and then the slightest touch of the gear lever will engage the next one of the six ratios. It really is both a practical and delightful little racing engine.

The handling too was remarkable – not just good but amazing. The little Minarelli sits on 2-inch wide tires but there was none of the nervousness which one might reasonably associate with such narrow rubber. On the contrary, it felt rock solid. It was only a lack of confidence which prevented me from dragging my knee sliders through corners.

Returning at the end of the session, I have to say that the pain from my knees, and my man parts, dominated my thoughts. I really would have been permanently crippled if I had raced that bike that bike for 20 minutes!

However, once the pain had subsided slightly, I was filled with respect for what Hans had achieved and I was in awe of just how good a racing motorcycle he had made. I have ridden many faster, more exotic and more expensive race bikes than the Van Bregt Minarelli, but none more impressive.