The Dolmar Dolmette is exactly as absurd as it looks: a genuine, operational drag motorcycle powered by 24 Dolmar chainsaw engines. It was built as a one-off in 2004, not a production model or merely a show prop.
The idea came from German cartoonist Rötger “Brösel” Feldmann, creator of the popular Werner comics, which revolve around beer, motorcycles and ridiculous homemade machinery.
Dolmette origin
According to Brösel, a neighbour who worked for Dolmar invited him to the company; he suggested that Werner would build a machine from chainsaws, and the Dolmar engineers reportedly replied that it was “fascinating nonsense” and agreed to do it. Dolmar’s Hamburg development engineers then created the machine with Brösel and his brother Andi Feldmann.
My neighbor works at the Dolmar company and invited me one day. Then the thought occurred to me: Werner would build a machine out of the chainsaws! The Dolmar engineers were immediately enthusiastic: “Fascinating, we’ll go along with it!”
Specs
What actually powers it? It uses 24 modified engines derived from the Dolmar PS-7900, arranged twelve on either side in two rows of six.
| Specification | Dolmette |
|---|---|
| Engine configuration | 24 separate single-cylinder two-strokes |
| Engine source | Dolmar PS-7900 |
| Displacement per engine | Approximately 79 cc |
| Combined displacement | Just under 1.9 litres |
| Power per modified engine | 7.1 hp, up from 6.3 hp |
| Combined claimed output | 170 hp / 125 kW |
| Torque at centrifugal clutches | 130 Nm |
| Torque after belt reduction | Approximately 400 Nm at gearbox input |
| Transmission | Harley-Davidson five-speed |
| Maximum engine speed | Up to 15,000 rpm |
| Length | 3.87 metres |
| Weight | Just over 300 kg |
| Claimed maximum speed | 260 km/h / 161 mph |
It is often called a “24-cylinder motorcycle,” but technically it has 24 entirely separate one-cylinder engines, rather than one conventional 24-cylinder block. Each retains a chainsaw-style centrifugal clutch, and, each engine must be pull-started individually!
The really clever part is inside the long central casing. Twelve specially developed ContiTech toothed belts combine the output from engines that are firing independently and asynchronously, reducing their maximum speed before feeding everything into the Harley gearbox. Dolmar first proved the concept using a little experimental kart called the Dolcart, fitted with three PS-7900 engines.
The PS-7900 motors were tuned from 6.3 to 7.1 hp apiece. Together they produced the quoted 170 hp and enough noise to exceed 130 decibels. Publicity at the time claimed it was louder than a departing Airbus. The MAHLE name visible on the bodywork isn’t merely advertising: MAHLE supplied the pistons and cylinders used in the engines.
Racing
Did they actually race it?
Yes!
After its initial test runs at Continental’s Contidrom test track in August 2004, it appeared at “Werner – Das Rennen 2004” at the Lausitzring that September.
Andi Feldmann rode the Dolmette against Swiss racing driver Christina Surer in a 450-hp Abt Audi AS400. Andi made a poor start, then rapidly closed the gap, but the Dolmette narrowly lost. So it was not particularly practical, but it really did run, accelerate hard and compete in an actual drag race.
The often-repeated 260 km/h top-speed figure should probably be treated as a claimed or calculated maximum, rather than a properly recorded speed. Before the race, Brösel himself described it as “at least 200, perhaps even 260 km/h.”
The lower photograph you shared shows the Dolmette being displayed at the 2004 Essen Motor Show, after its racing appearance. That separate Dolmar chainsaw beneath the front of the motorcycle was part of the display; it wasn’t an auxiliary 25th engine.
In short, it was a genuine Dolmar engineering exercise wrapped inside a Werner-style publicity stunt… and possibly the most complicated way anyone has ever found to combine 24 perfectly good chainsaws!
Dolmar’s original articles
Dolmar shared the story of the Dolmette on their website which no longer exists as a live site, but can be found on the Wayback Machine. The following has been reproduced from this source.
The DOLMETTE
Engineering “Made in Germany” compared with a Norther-German Comic Star created her: The DOLMETTE. A wired bike with 24 DOLMAR chainsaw-engines.
View the developement diary here.
Technical facts
The engine
What makes the Dolmette unique in engineering terms is its 24-cylinder 2-stroke power plant. Nothing quite like it has been seen before. The combined power of 24 DOLMAR chainsaw engines is fed into to a 5-speed Harley-Davidson transmission by a series of twelve toothed belts.
The engine in question is the one used in the PS-7900 professional chainsaw, which currently boasts the best power-to-weight ratio of any professional petrol chainsaw in the world – just 1 kg per PS. In standard trim each of these high-performance air-cooled 79 cc units generates 4.6 kW of power (6.3 PS) at 9500 rpm. A specific output of 59 kW per litre is outstanding for a chainsaw, and the secret lies in DOLMAR’s High Performance Combustion (HPC) technology. This term refers to the special design of the six gas exchange ports in combination with the asymmetrical combustion chamber head and the crankcase configuration: the result is a highly efficient combustion cycle with low exhaust emissions.
For use in the Dolmette the engines were tuned and tweaked to deliver 5.2 kW of power (7.1 PS) at 10,000 rpm. Maximum torque delivery is 5.5 Nm at 7,750 rpm. When all 24 are combined, the result is a 24-cylinder power plant with a total displacement of 1.9 litres, a power output of 125 kW (170 PS) and 130 Nm of torque at the centrifugal clutches.
The combined power plant
The heart of the combined power plant is the central drive belt casing of aluminium construction. As well as encasing the eleven belts used to couple up the individual engines, it also houses the exhaust ducts for the cooling air. Twelve engines are mounted in two rows of six on either side of the drive belt casing. Each engine is held in place by means of two threaded studs that normally serve to secure the guide bar to the chainsaw power head. The individual motors are coupled together in sets of three by means of a double-sided drive belt, making up eight modules in all. The individual engines are not rigidly connected; instead they deliver their torque through the centrifugal clutch that is a standard feature of every chainsaw.
Through a sequence of three more toothed belts the power of the eight modules is transferred to a single output shaft, which in turn drives the clutch for the 5-speed transmission via a twelfth belt. The toothed belt drive also serves to gear down the speed of the high-revving chainsaw engines in the ratio 3.45 : 1, producing a manageable maximum of 4,500 rpm at the transmission unit. The friction loss that is inevitable with belt drives is less than 10%, which means that the maximum torque available at the transmission input shaft to power the bike is a massive 400 Nm.
As a consequence of the non-rigid coupling of the individual engines via their centrifugal clutches, the combined power plant has a self-determining – i.e. totally random – firing sequence. In this case, because of the way a 2-stroke engine works, there are 24 ignition points during each engine revolution, or roughly one every 15º. In other words, this power plant fires four times more often per revolution that a 12-cylinder 4-stroke engine!
The chassis
The central element of the frame is the self-supporting drive belt casing with an overall length of 2,495 mm. Bolted onto this is the front section of the frame, constructed from 32 mm tubing. Sitting in the steering head is the Techno Plus front fork, machined from the solid, with telescopic dampers. The bolted-on back fork assembly is likewise constructed from 32 mm tubing and accommodates the back wheel with no suspension travel. The back wheel is a massive 8½” solid disc wheel fitted with a 240/40 × 18” tyre. At the front is a more conventional 3½” aluminium spoked wheel shod with a 120/90 × 18” tyre.
The fully assembled bike measures 3,870 mm from front to back and is 590 mm wide. As the power plant is largely built from aluminium and magnesium, and consequently weighs a modest 188 kg despite its 24 cylinders, the overall weight of the Dolmette has been held down to a touch over 300 kg. This has resulted in a very favourable power-to-weight ratio of just 1.8 kg/PS.
A machine that goes this fast also needs to stop fast. The front wheel is fitted with 292 mm twin disc brakes with 16-piston calipers. The back wheel has a single 292 mm disc teamed with a 4-piston caliper.
The race: DOLMETTE vs. Abt Audi AS 400
In an exciting speedway duel Andi Feldmann on the DOLMETTE loses by a hair.
On 4 September 2004 the EuroSpeedway in Lausitz was the setting for a gripping race between Andi Feldmann on the DOLMETTE and racing driver Christina Surer in her Abt Audi AS400.
Because the start of the race had been fixed for 5.00 p.m., and Christina Surer was running on a very tight schedule, there was only a 20-minute time slot in which to run the race – and that included the time needed to get the DOLMETTE’s multiple engines powered up for the start. The intense pace and pressure soon told on the charming pit crew, the ladies’ handball team from Süderbrarup, who only managed to get 20 of the DOLMETTE’s 24 engines running. So Andi Feldmann had to make do with the power output from just 20 chainsaw engines – a “mere” 142 PS.
The drama and stress took their toll of DOLMETTE rider Andi Feldmann too. During test runs in Schleswig and on the Lausitz Eurospeedway, for which unfortunately only two days were available, it became clear that the torque delivery from the 24 engines, even in second gear, is just too much for the back wheel to handle. Consequently the bike suffers from massive wheel-spin. For this reason Andi Feldmann left the starting line in third gear, and with power output already down by four engines he simply couldn’t get the standing-start acceleration necessary.
And then there was his opponent. Christina Surer is a highly experienced racing driver with ice-cool nerves. At the starting gun she needed only a few milliseconds to put down all the Audi’s 400 horsepower onto the tarmac. Andi Feldmann, on his 142 PS DOLMETTE, needed nearly half a second more. With his engines revved up to full power Andi managed to make up some lost ground, but he was unable to prevent Christina Surer from snatching victory by a whisker.
That’s the end of Dolmar’s article from the Wayback Machine. So, do you think the Dolmar Dolmette is cooler than the STIHL Chopper?
