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In a small workshop, the brothers Hans and Heinz Emmerich began the development of the first small two-stroke engine. At that time, the "lightest" industrial engines weighed as much as 35 pounds. On June 20, 1948, the same day as the Germany Currency Reform took place, the first KMS 30 (KMS = KleinMotoren Stuttgart) engine was born. Intended as a power source for portable machines, the KMS 30 weighed only 14.3 pounds yet produced 1.2 HP, which was an incredible feat for that time.

From 1948 to 1971, Solo manufactured various pieces of agricultural equipment as well some scooters and other vehicles. In 1971 they introduced the Solo moped.


The most common model imported to the US seems to borrow heavily from the engine and drive train designs of the Batavus M48 and Peugeot 102. Most US models were step through, single speed mopeds. A some what rarer version had a two speed transmission with a unique clutch. Some Columbia mopeds came with slightly larger bore Solo engines equipped with variators. Drive train is v-belt and motorcycle chain is used for the main drive. It has a separate bicycle chain and sprocket setup for starting and auxiliary drive.

The Solo moped had only one unusual aspect. It was manufactured with a primitive water cooling system. This system consists of a coolant filled water jacket in the cylinder and nothing else. Without the radiator, pump, and hoses normally associated with water cooled engines, the Solo engine appears ordinary.


The Solo motor is Schnurle ported aluminum cylinder and case. The transmission is external. Intake is through crankcase reed valve induction. All Solo cylinder liners also include a boost port. On some engines the boost port is not completely drilled through the cylinder. All Solos use a 10mm Bing carb with a "screw off" bowl. The cylinder includes a water jacket filled with coolant.

Useful Info

This info is from a NOS Solo engine intended for the Columbia moped version. There are minor differences between this engine and the engine on the actual "Solo" brand moped engine. The engine on US single speed models has a slightly smaller cylinder bore.

  • Displacement: 47.6cc
  • Flywheel Puller 26x1.5 thread. It is the same puller as many Husquavarna and KTM motorcycles.
  • Spark plug: Original is a Bosch W5A. The standard moped NGK B5HS works as well.
  • Coolant: Standard automotive green coolant works well. 50% coolant 50% water for most climates.
  • Exhaust port timing: 150 degrees
  • Transfer port timing: 120 degrees
  • Boost port timing: 100 degrees
  • Crank bearings: #6202
  • Clutch side crank seal: 26x35x7
  • Magneto side crank seal:15x30x7 (original seal is printed 15x35x7)
  • Stroke: 41.8mm
  • Bore: 38.5mm
  • Piston diameter: 38.46mm
  • Intake I.D.:11mm O.D.:16mm
  • Reed valve gasket width (compressed): 0.4mm
  • Crankcase center gasket width (compressed): 0.2mm
  • Carburetor: 10mm Bing Type SRB # 1/10/112
  • Cylinder base gasket width(compressed): 0.5mm
  • Rings:Rectangular cross section with cutouts for round pin at ends. Height: 1.5mm Width: 1.5mm
  • Head gasket width(compressed): 0.6mm Note that because of the water cooling system you cannot eliminate this gasket.
  • Wrist pin diameter: 10mm
  • Con Rod little end I.D.: 14mm
  • Condenser: Bosch with number 1237 330 037 and also number 041
  • Points: Bosch # 1 217 013 021 (not confirmed but appear to be the same as some Sachs and Puchs with Bosch ignitions)
  • Stator plate: Bosch number 1 217 031 415 also marked V/1 12394. 5 wires.
  • Flywheel: Bosch 6V22-5/10W Numbers:0 212 124 039 also:RDP1 also:042 also:084
Stock port map provided by Ilana Mullin of curiouspear designs