Re: 1934 Packard bearings
Posted by Owen_Dyneto On 2014/3/24 9:57:11
It depends a bit on what kind of driving experiences you anticipate. Lots of approaches have been tried, some successful, so not so successful. Remember that babbitt is very protective of the crankshaft by its ability to embed small particles; the journals were shot-peened before final machining in the babbitt era, but also hardened with the adoption of inserts. Also the original inserts were flanged bearings and the sides of the flanges were also babbitted to ride against the cheeks of the crankshaft and determine rod end-play. The conversions I'm familiar with (I'll attach an old CCCA article though other conversion ideas have come along later) use brass weld buttons on the side of the rod to make up the space. Also some of the conversions require notching of the rod bolts - again something that doesn't sound like a good idea. One advantage to babbitt is that it can be finished to any diameter required - for example if only 0.003 was required to bring journals back to true, then you just sized the babbit to that undersize rather than jump to 0.010 or 0.020 or whatever the next undersize insert was available in.
Keeping engine speeds within the original design limits should give babbitt bearings a life of 80,000 or more miles, sometimes many more - heat (from high engine speeds) is the major enemy of poured bearings and Babbitt became problematic as roads improved the opportunities to drive faster became more common. A couple of prestige restoration shops that I'm familiar with that restore these engines, not just for show but for touring, stay with poured bearings on engines that were originally done with Babbitt. My own 34 Eight went 83,000 miles before I finally heard my first hint of a rod knock and decided to rebabbitt - that's not much less (if any) than the life of the inserts - again assuming you drive at speeds that are consistent with the conditions of the time. If you're going to install a high speed rear and plan on a steady diet of 65 or more mph, then I'd give a conversion some serious consideration, otherwise not. Another factor to consider is the cost of removing and reinstalling the crankshaft counterweights if the journals need resizing - its necessary when doing babbitt as the bearing surface is the full width of connecting rod big end; the inserts when done by Mr. Shower's method have a smaller (narrower) bearing width and apparently you can get away with not resizing the full width of the crank journal and hence not removing the weights.
Attach file:
(239.48 KB)
(262.85 KB)
Keeping engine speeds within the original design limits should give babbitt bearings a life of 80,000 or more miles, sometimes many more - heat (from high engine speeds) is the major enemy of poured bearings and Babbitt became problematic as roads improved the opportunities to drive faster became more common. A couple of prestige restoration shops that I'm familiar with that restore these engines, not just for show but for touring, stay with poured bearings on engines that were originally done with Babbitt. My own 34 Eight went 83,000 miles before I finally heard my first hint of a rod knock and decided to rebabbitt - that's not much less (if any) than the life of the inserts - again assuming you drive at speeds that are consistent with the conditions of the time. If you're going to install a high speed rear and plan on a steady diet of 65 or more mph, then I'd give a conversion some serious consideration, otherwise not. Another factor to consider is the cost of removing and reinstalling the crankshaft counterweights if the journals need resizing - its necessary when doing babbitt as the bearing surface is the full width of connecting rod big end; the inserts when done by Mr. Shower's method have a smaller (narrower) bearing width and apparently you can get away with not resizing the full width of the crank journal and hence not removing the weights.
Attach file:
(239.48 KB)
(262.85 KB)
This Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=141469