An Example in Steel  Casting  --  Lever Arm in the BMW Engine Valve Train

Lever Arm Performance Requirements 


Top and Bottom Views of the Intermediate Lever Arm with Rollers Installed

The intermediate lever arm is a precision component designed to minimize the weight and inertia in the valve train, but still provide high strength and stiffness.

The lever arm has to withstand high cyclic stresses and aggressive wear conditions over the full life of the engine, requiring a steel alloy that has:

  • Ultimate Tensile Strength = 263 ksi / 1870 MPa 

  • Yield Stress = 242 ksi / 1670 MPa

  • Surface hardness of 70 Rockwell C measured with 
    a Vickers microhardness tester 

  • Core hardness of 37 Rockwell C

The precise mechanical action in the valve train depends on tight  tolerances on the critical dimensions of the lever arm --  +/-0.05 mm. 

  • Finished components are 100% inspected and classed into six tolerance bands, each 8 microns wide. Classed parts are used as matched sets in individual engines.

  • Appearance -- Uniform, blemish free appearance with an oxidation layer after plasma nitriding.


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