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.