Originally posted by Boulderado:
Okay, so at the risk of exposing my ignorance, why is pressure oil better than the splash oil or whatever system the old 235s and 216s have?
No ignorance, it's a good question. Here's an answer:
Way back when, in the days of steam engines, engineers discovered certain alloys that would tend to "hold" oil better than average. With open exposed bearings and "occasional" lube this was a good thing. Plus, the alloys were soft, so they wore insteand of wearing down the expensive steel bits.
This system evolved to one where the best way to do a bearing was to build the rod and journal kinda loose, then pour the metal in and let it cool. Then you scraped down the high spots, and you were good for quite a while.
There were two drawbacks: it took some labor to hand fit. Also, the soft bearing metal was, well, soft, so as the load on the bearing increased it tended to 'smush' out. As it smushes, clearances open up, and the increased play makes the rod hammer, or pound, that much more. Hence the name babbitt-pounder.
Finally some bright guy came up with the idea of the shell bearing. It's still babbitt in a way, but different. It's mostly steel, which is hard of course, but with a thin layer of babbitt plated on. So, it doesn't squish out.
The second big improvement was to pump oil, under pressure, into the bearing so that the whole thing sort of hydroplaned on a thin layer of oil. Once it was running, metal never touched metal.
Put these two things together, and you get bearings that go 100K miles or more w/o service. That was unheard of in the old babbitt days.
Can you run babbitts today? Well, yeah. You can still use horses, or use a steam train. Both are way cool. Both are a !@#!@# lot of work, too. ;-)
Cheers!
George
