I'm about to have a machinist line bore the main bearings on a P-Type block.
From Bob Jones' article on engine rebuilding he states the oil grooves in all the main bearings should be at least 1/'4 wide and 0.150" deep. Could anyone add any further information on this topic? For instance on the rear main what measurements are suggested for the second groove which is fed by the 1/8" oil hole?
Has anyone considered cutting oil grooves part way across the axis of the bearings to give a fuller flow of oil, as the machinist has suggested?
Any help and suggestions on this oil feed topic would be well appreciated.
I cannot comment on the general dimensions of the oil grooves other than to say that I am sure that Bob Jones' advice is as expert as it comes.
However I do not think that I would follow the advice of your machinist and make grooves around the periphery of the bearings. This, I know, is modern advice to increase the volume of oil flowing through the bearings and thus help heat dissipation. This is advice suited to modern lubrication systems which are designed from the outset to be high volume flow, relatively low pressure systems.
Conversely our systems were designed on the high pressure, relatively low flow principle - as I can remember Mike Allison explaining to me late one night in an Abingdon noggin pub. You have only to compare an A-series centrifugal oil pump with our close fitting gear pump set up to see what I mean.
Therefore my doubt would be that our pumps could not maintain sufficient oil flow at the lower pressures introduced by more freely flowing bearing groove systems. Possibly disastrous, but the decision and the risk must be yours.
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Posted - 26/11/2008 : 17:14:06
