The rule of thumb is the belt must lay fully in the pulley. The top of the belt should be flush with the pulley. Wrong angle cut on the belt or too wide will not grip as well and will wear prematurely.

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81 300CD (sold) 1972 280 SEL 4.5 (sold) 1966 250 S 4 spd (sold) 1974 450 SL (sold) 86 BMW 325ES (sold), 1973 280C (sold) 1988 300 SE.