One of the greatest of the motorcycles that failed to survive, but was important to the technological advancement of motorcycles, is the German built Windhoff 750 that broke new ground and initiated technology that lives on today.

the 1927 Windhoff 750 is arguably the most important motorcycle developed between world wars, and that includes surpassing even the Brough Superior SS 100.

Although both expensive and exclusive, four-cylinder motorcycles were not unknown in pre-war days – Henderson, Indian, Ariel and Nimbus being among the most successful - but few were as technologically advanced – or as imposing – as the German Windhoff. It was introduced at the Berlin Show in 1927.

the 746cc engine was a four cylinder, four stroke, and it used an overhead cam. It had cylinder liners and internal oil liners

This was a first for a four cylinder motorcycle and now common in the majority of production bikes and modern superbikes. The cam operated in an aluminium head and directly activated the valves via a series of cogs run off the camshaft.

Not only was its overhead-camshaft engine oil cooled, it also functioned at the motorcycle’s frame. The crankcase and cylinder block were combined in a monumental alloy casting, to which the steering head was directly bolted, while four straight tubes supported the rear wheel.

it weighed 400 pounds, and had 22 hp

http://www.pipeburn.com/home/2015/11/30/1927-windhoff-750.html#
https://www.bonhams.com/auctions/16230/lot/523/