I have pondered this over the years. If you consider the bearing shells need to be supported to the maximum degree on the thrust side of the rod this would mean the locating tabs would be towards the front of the engine. Positioning the rod like this means the hole points towards the flywheel. Is the hole necessary? Well if there is a hole it is there because of some engineering consideration in the past. Is it effective? Who knows? In all honesty a 3/64" hole flashing past a 1/4" hole for a nanosecond ain't gonna pass much oil. To lubricate the bores, overflow from the timing bush onto the crank cheek may do the timing side, but most oil will come as overflow from the cam trough, onto the flywheel and up the bores. Perhaps this is why we have the hole as a back up on cold start up, the timing side overflow lubricating the right hand cylinder. Of far more importance is the area where to oil exits the crank on the big end journals. When new the oil hole in the crank was at the bottom of an oval shaped cup, machined into the journal. While this reduces the total bearing surface by a small amount, it has the effect of allowing a wider film of oil to be deposited on the shell surface. As the cup is in effect conical, those who did Calculus will be familiar with the relationship of surface area to depth, typically demonstrated by an old style Martini or Babycham glass. There is a huge reduction of surface area for a small reduction in depth. So, as the crank is reground, each grind removes more of the available surface area for oil to be spread across the shell. Also when you get your crank back it is treated with care, we avoid touching those journals. But in fact the grinding process has left the oil hole with a razor sharp edge, ready to gouge a neat groove in the shell. so if you are having a crank done, reinstate the cup with a Dremel Grinder first, get the crank ground and then make sure the edge of the oilhole has a nice smooth lead onto the journal surface. I consider this to be a better way of improving oil flow. The Glyco Bearing Website has a wealth of information about crank grinding, journal polishing and bearing selection. After reading it you will wonder whether your grinder really knows what he is doing. Swarfy.I cant comment on the hole but the advice one dealing with the cleanup after regrinding is obvious and important , its basic standard practice but not always done, being in engineering most of my working life, ive seen the results.
