Going on a diet

The motorcycle racers of today have at their disposal a host of exotic materials by which to make parts lighter, and even stronger as compared to the past.  Titanium bits and pieces are ubiquitous in todays paddock. 
Carbon fiber has revolutionized motorsport, and has even found its way into production bikes.  (ie the HP2 Sport). 

Guys racing before such exotic materials were available resorted to more practical solutions for decreasing the weight of a bike.

Of course a race bike would not have the routine road going accoutrements such as lights, horn, signals, etc.  Casting material for many bikes differed from the pedestrian models as well.  Elektron, a magnesium alloy, was used extensively on works bikes and even by privateer racers before and after the war. 

Any part on a bike that could be lightened, while maintaining its integrity, was subject to a diet.  For sheet metal parts, this often meant drilling holes to reduce the amount of material.  Simple things like changing a steel drain plug to an aluminum one, would amount to a small reduction in weight.   But when multiplied by the number of plugs on the bike, could add up to real savings at weigh in.

Pictured above are two drain/fill plugs. They are M14 x 1.5.  The plug on the right is a standard issue item found on most pre 1969 BMW motorcycles.  It is SW 19 (SW = schlüsselweite = width across flats, or wrench size).  Material is steel, cadmium plated.

On the left is a "lightened" racing version.  While still the same thread diameter and pitch, the length is slightly shorter, and it is SW 14.  The material is aluminum.  

The steel plug weighs in at 29.3 grams, while the aluminum plug weighs 6.8 grams.  (A 77% reduction in weight.)  If you multiply by 5 (the number of plugs on a transmission, final drive and oil sump), the weight savings is a quarter pound.  Not huge, but the effect is additive when other weight saving meaures are employed.