Short Stroke Engine ] [ 86mm Crank ] 5 Gearbox ] Cams ]

86mm Crank

Alpha Bearings produced a steel pressed up crank. The result looks excellent, but their original 2 month lead time turned out to be 5 months. The brief to Alpha was to produce an 86mm stroke crank that would fit straight into my existing cases which previously housed a standard 100mm throw, cast iron flywheels with a bolt up INA big end. The crank had to be good for 7000rpm on a regular basis and indestructible at 8000rpm.

The new flywheel has been set to balance at the same factor as the old assembly with a piston of 441 grams. The apparent balance factor of 56.77%.

NewCrank1.jpg (121031 bytes)    NewOldCranks1.jpg (80699 bytes)

Side by side you can see that the mass of the old crank is more distributed to the outside of the wheels. This means that the new crank should be easier to spin up. It is also a couple of hundred grams lighter than the standard, 11.4Kg including the rod as opposed to 11.1kg including the rod. All this and the short stroke should give me the 7000 rpm I am after!

NewOldCranksPistons.jpg (215404 bytes)