Re: Insert bearings
When conversions were in their infancy on the Model-A/B blocks, and when we were using multiple bearings within the main bearing web, machinists would use an end mill and create a way for the oil to feed the hole in each of the bearing shells. When Rich created the one-piece bearing, this eliminated this op.
My personal take is that the 'art' of casting bearings has improved greatly to the point where the longevity of casting bearings exceeds what is available for the inserted bearings. The availability of top-quality "Babbitt", the knowledge of how to pour, peen, and burnish properly, -and the use of good quality line-boring machines (such as Tobin-Arp or Berco) that are rigid and use a hydraulic feed have been the game changer. For these reasons, we are seeing owners with failed bearings converting back to cast bearings. I liken insert conversions to electronic ignition conversions, powder painting, and hydraulic brakes where each had their day where they were considered necessary, yet all have seemingly failed the test of time and now deemed not superior or necessary.
On your own engine, two things that would scare me as an engine rebuilder. If the soft metal has failed on your bearings due to lack of oil, I would want to inspect/mic the crank journals carefully as I would expect to see a surface finish deterioration and wear that would cause the journal pin to be out-of-round. Also, when you 'carve' a groove for the oil to transfer, you will likely disturb the bond of the soft metal which could cause flaking and you will likely cause the soft metal on both sides of the groove to rise above the surrounding areas potentially causing scoring on the crankshaft.
One other thing to keep in mind is ensure you do not allow an insert bearing to roll or spin in the cap or in the block as this will distort the cap or block generally requiring both to be line-bored again.
|