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In the early days, the various 2-speed engines differed greatly in their primary transmission. Primary drive was via either a chain, a toothed belt (syncroflex), or geared cogs. The gear with cogs gradually won. The next steps in the transmission, still within the engine, also came in various types. NSU used their own patented principle, which ensured that drive efficiency in second gear was as good as with single-gear models. Zündapp followed a similar principle for a time; after the primary gear they used a single step planetary gear which had an engaged and disengaged position.

However, it was an entirely different third type that prevailed, viz. a gear with a primary cog wheel that drives an intermediary shaft with 2 (or more) fixed cogs placed side by side. These cogs are in permanent mesh with a corresponding set of output cogs. The output shaft has a engagement mechanism, which locks onto the selected gear wheel while the others cogs run freely. The clutch in the engine type described above is mounted to the crank shaft or the countershaft.

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ILO G50 Piano with 2 gears.

The output torque from the crankshaft is transferred to the countershaft via a toothed belt connecting to the clutch. Both the output shaft’s cogs are in constant mesh with those of the countershaft. The shifter gear passes on the torque to the output shaft via a claw clutch and a grooved cog.

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The Derby Ferrari came with all types of primary transmission.

From left to right, the syncroflex belt-drive, then cog-drive with the large etronax plastic clutch wheel, and far right chain-drive.

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Here is the “famous” Ferrari gear, which functions in the same way as the ILO gear.

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As an afterthought, here is a further development of the Etronax cog clutch (by request from Diesella).

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The classic 2-speed engine with kick-start made by Express

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This engine differs from the Derby in several respects, most notably in having the clutch on the actual crankshaft.

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