Date: Tue, 10 Dec 1996 17:40:54 -0800 (PST) From: Mike West Subject: Bearings stuff (no numbers) It's still raining and my heads are coming along nicely. I'm bored, so I sat down and wrote another item of ignorance. When I finished the List piece on the Piston and horsepower, I went looking for the efficiency of the over-all engine versus the theoretical. This, I felt would give me a look at friction and unbalanced mass etc., all in one fell swoop. By the time I discounted for the alternator,(3-5hp)and the fan, (10hp at max rpm) I had such a small number left that it really didn't mean anything. Maybe the pitiful number I had left is the friction and maybe it's not. I'm a failure as an automotive engineer. :-) Even the numbers above are estimates I've heard. When you think about all the other forces and heat sources involved, friction really is insignificant. Still, we need to know what's happening down there, right? Paid big bucks for that engine and want it to be happy, right? The journal bearing has been around since the caveman. He invented it to please the women-folk I suppose. Along with the wheel. Dragging that sled was a bummer. They tried replacing it with roller bearings, it isn't any better. Won't even go as fast as I recall. Basically the bearing never touches the babbit lining while running. It surfs on a layer of oil about .001 thick or more and squishes any excess out the sides. I say "surf" because that really is the condition. Nose up and riding the wave. This is an automatic feature when you have a shaft a couple thousandths smaller than the bearing. Along with a good supply of oil to ride on. On the piston sleeves, you'll find a taper at the bottom to pick up that oil. And drop out the crap I think. I am not going to tell you about what oil to use. It has become a religion with people and I don't want any cross-burning on my front lawn. So we have four pretty hefty main journals on the crank, four big diameter but skinny ones on the rod ends. Four more little but long long long ones on the wrist or "gudgeon" pins. They have done their job for a lot longer than I've had reason to think about them. When you come out in the morning and start up, the journals are all sitting right on the babbit liners. One point contact. Metal to metal. Let's look at that. You fire up and it takes from 10-30 seconds to get oil to the journals. If you've been good, maybe less, if not, then maybe longer. There was some in there but we're talking "up to pressure". For that average of 20 seconds the steel crank etc is just scraping along on the babbit. Little bit of oil from last nite, no help. The babbit liner is a lubricating material itself or you'd hear some terrible noise back there. It tends to "spall" from pressure.(flake) Babbit has also been around since "almost caveman". They change the alloy a bit every once in a great while but it's still basically the same stuff your grandfather used. Still, you are wearing it away every time you start the car. It's fact Jack, the law, the big T. You can not stop it it keeps right on doing it no matter who you pray to. Now that same liner is the one I so carefully put in there with plasti-gage check and it was about .004", pretty good. Within tolerance. Truth here- those are the damn bearings I bought and they have nothing better. It could have been 1-1/2 thou. according to the book. Thats' the minimum. Twenty seconds at 900 rpm, thats about 300 revs on the metal. You know those people who come out on the cold morning and as soon as it starts they wind it up to 4000? " It warms up faster" they say. They got you there bud. Metal on metal does get hot faster. Getting on with the tale, The side clearance, between the rod bearing and the crank? It was about ten thousandths, min is .004" and max is up to .028 including the wear limit. The piston holds it in place, why worry? That's where the oil squishes out, big deal. It also controls how much oil pressure there is for the surfer. Now, well talk about particulates. That's a nice word for all kinds of crap. You got an air filter on your carby? Is it a good one? You know those engine seals Bob is always on your case about? The sand dune boys change oil and all filters after every days run. The off-roaders change the oil every time they have a pit stop and that was just to get a new air filter. Because all of that dirt and sand ends up in the crankcase. Then there's just plain carbon. The black stuff. The stuff you use to gauge when it's time to change the oil. "Look, it isn't even black yet"! These are all sold under the general category of "abrasives". Now we segue into generalities: All engines, be they from Detroit or Italy or Japan or even Germany are all built of the same materials and components. All but one, have oil filters. OK, so maybe there's others. :-) Go ask one of these bush mechanics or even a real professional in the rest of the trade what the symptoms of low oil pressure mean. He'll talk to you, we're all in this together. He will not tell you about a bad oil pump, or get a bigger one, or oil relief valves, or your pick-up tube may be flummoxed by energy beams from alien space ships. They're a possibility but remote. What he will say is "your bearings are shot, guy". I have a feeling he's right. If you can't buy that, go ask your grandfather. west