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 Ill have a few words on the mysteries of spit and hope oiling.