Exhaust valve guides in the Mini Cooper 'S' and in the 650 cc and 750 cc BSA-Triumph motorcycles were manufactured from Hidurel® 5, chosen to carry heat away from the valves and seats fast enough to protect them under sustained high load.
Extracting high power from these relatively small engines imposed considerable thermal stress on the valves and valve seats. Protecting both depended on rapid heat transference through the surrounding material, alongside other mechanical demands.
Hidurel® 5 (UNS C64711, DIN 2.0855, DTD 498) is a high strength bronze with high thermal conductivity. As a valve guide material it gives heat a ready path away from the valves and seats, helping maintain port seal efficiency. It also offers good wear resistance and anti-frictional qualities when running against heat-resisting valve steels, and its matching coefficient of expansion permits the close working tolerances that optimum engine aspiration requires.
The alloy proved its value through many wins on the international motor racing scene in the late 1950s, which prepared the way for widespread use on the roads of the world through the 1960s.
