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The design of the 3- and 4-speed engines is more or less identical. Torque is transferred from the crankshaft to an intermediary shaft via cogs. From here it’s passed on to the output shaft via the selected gear. The clutch was placed either on the crankshaft or the intermediary shaft. The two engines did, however, differ in terms of their method of gear change. While gear change on the 3-speed model was carried out with a twist-grip, the 4-speed model had a foot pedal/lever. Foot gear change was a prerequisite for sales to young men, who really wanted to ride motorbikes.

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Rex 3-speed with the clutch on the crank shaft

This illustration provides a good overview of the basic construction of the modern engine type.

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Zweirad Union 805 3-speed engine with the clutch on the intermediary shaft.

On this engine the detachable cogs can be locked to the output shaft with special balls.

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SCO Type 3

In most respects the SCO motor and the ZU motor are identical, but their method of gear change differ slightly. In stead of balls, a catch (SC214) which can be shifted to the selected gear is used.

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Everton 4-speed engine by FBMinarelli.

This arrangement is, again, in principle the same as with the SCO and the ZU, only with foot-change. This motor also has an extra gear, and for changing gears cam-controlled shifter forks are used. These are in constant interlock with the shifter gears, which have claw clutches.

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