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This is the 9th in a series of articles. Just a few more mods for those with 1 1/2” crankshafts using slipper style bearings. Oil flow through the crankshaft and ultimately out the bigend is, in the Austin 7 pressure fed engines, not the ideal arrangement. The oill has to travel the entire length of the crankshaft and still maintain pressure an flow. Flow at number 4 bigend being the main objective. To achieve this, conrod side clearance needs to be more than normal. Side clearance needs to be:- At number 4 bigend - 0.030” to 0.040” At number 3 bigend 0.020” to 0.025” At number 2 bigend 0.015” to 0.020” At number 1 bigend 0.010” to 0.015” Crankpin clearance on all bigends needs to be 0.003” to 0.004” Oil pressure at 6000rpm - minimum 80 psi (100psi preferred). To achieve this, oil supply to other parts of the engine needs to be reduced:- Front camshaft - make new bush with oil feed hole maximum 1/32” diameter. Rear camshaft bearing - bore and sleeve with 1/64” diameter feed hole. When making the new front camshaft bearing, having the camshaft journal reground is recommended, the bearing running clearance should be 0.003” to 0.004”. Next time I’ll have a few words on the mysteries of spit and hope oiling. John Bowring |