Babbitt vs bearings

One reason is, I believe, that the soft Babbitt material will "absorb" tiny bits of metal that would otherwise scratch the polished bearing surface of the crankshaft.

Couple that with the ease of manufacturing, like casting bullets, and relative cheapness factor compared to the other (insert one) bearings.

Where's an expert when you need one?

The Babbitt does catch the tiny bits and do scratch the crankshaft. between a soft material and hard one, the hard one always recieves the scrathes, same with rings and the walls of the cyclinder., A lot of motorcycles use the needle or ball bearings in there engines, some aircraft do as well.

Hi,

Plain or white metal bearings are quieter in operation and are generally more tolerant of chemical pollutants in the oil than the rolling contact variety. This is particularly important in the internal combustion engine were lubricants are used to remove heat from the underside of the pistons and tend to become contaminated with the products of combustion quite quickly.

Remember also the application with the problem of having to use split cage arrangements to permit the assenbly of the bearings onto the crankshaft journals and the crankpins and I think you will appreciate how the ''babbit'' type shell bearing is still the most cost effective solution

Mmmmm,

I get the easy and cheap part, and riding on oil film (which is pretty amazing actually).

But I would think flushable caged bearings would be less sensitive to contamination (well, then I consider that it is filtered and pressurized...) OK, so if we were using loose crank case oil maybe rolling bearings would be better?

But how you would install them does remain a question.

Yes, babbitt...cheap, easy, easy to install, and they work good enough.

Assembly of an engine with roller/needle bearings? Mercedes used something called a "Hirth" built-up crankshaft in the 1930's in Grand Prix engines. I think (I may be wrong, but I have a technical article somewhere here with the details I'll look for to confirm this) these used roller/needle bearings. The crank was assembled from pieces.

I'm also thinking Porsche used some roller/needle bearing crankshafts in the past.

Two interesting factoids: A number of modern Grand Prix engines don't use rod or main bearings; they are using special surface treatments, coating and oil control strategies to eliminate the bearing mass.

Second: the late, great Smokey Yunick of Indy 500 and NASCAR racing fame built a needle/roller bearing small block Chevrolet engine years ago to see if there were performance improvements. Didn't help in that application.

Smokey Yunick

Way ahead of his time!

You have the installation problem correct, but another consideration is oil pressure. The babbitt bearings help to maintain oil pressure throughout the system. The oil galley's would have to be revamped to provide proper lubrication for all the bearings, not just the crankshaft - again back to expense.

Thats it, the problem is that you'd end with a crankshaft with several separated parts to allow bearings to be assembled in place. Imagine a 8 cylinder engine, you'd end with a minimum of 9 parts to assemble. Think about 9 different parts that must have ground diameters for bearing mounting, all aligned to a close tolerance, and keyed to result in the correct piston timing, plus mounting and holding devices like bolts, nuts, washers, locking devices, and all must e balanced... uh, bad feelings about that, imagine all that stuff in an assembly line that must output hundreds of units per day.

The option is a 1 piece forged part that can be balanced and ground in the line, and have everything it needs right away from manufacturing. Much better.

Actually, I have read that some historical engine models, high performance racing ones, have experienced the use of bearings in the crankshaft to minimize internal atrict. It seems that the problems do not compensate for the gains.

Hum, by the way, some model engines do have bearings in the crankshaft. However, they are high performance ones, cost more, and, obviously, are much simpler 1 cylinder engines. Quite nice ones: about 1,5 hp with .46 cu.in. around 12000 rpm. Cool!

GA from me for a nicely written answer.

Some model engines are revving even higher I am lead to believe, I had a quick look around on the internet and relatively large engines can still exceed 20,000 RPM.....amazing!!

I understand (though I'm not an aficionado of the sport) that Tourist Trophy motorcycles (TT, in the parlance) using 50 cc engines (boy THAT'S tiny) at upwards of 60,000 RPM, produce speeds in racing of 125 MPH. I can't imagine the kind of specific power output per cc it would take to do that, and the speeds that the parts have to travel at, using anything less that needle, or similar bearings. In fact, diamond bearings wouldn't seem out of place to me, for an application like that!

Micah

I have to admit to being pretty impressed with my kids car (just your run of the mill inline 4 in an MR2) with a redline out at 13K

I find these kinds of revs listed unimagineable.

I agree with you and would like to add a little information about mass produced motorcycle engines. In the late 60's and thru the 70's anti friction bearings became the norm in multi cylinder motorcycle engines. Often times the rod "big end" had "needle" bearings and the crankshaft bearings were "ball" type. The crankshafts were a pressed together affair of many pieces like you suggest. Some of the modified stock engines had "welded cranks" because the higher racing loads would sometimes twist the press fits and destroy the engine.

In the 80's the plain bearing crank became the norm again in high output multi-cylinder production motorcycle engines. I believe product development had progressed to allow the less complicated plain bearings in these relatively high output engines. The engines became more compact and thus lighter than the more complicated pressed together affair.

Of coarse there are lots of different combinations that companies made work. McCulloch on many of their high performance two stroke engines used loose needle bearings on the rod "big end". The crank was one piece but the rods were two piece and you had to lay the needles in one at a time then put on the rod cap. More than once I was looking for the needles on the work bence after I dropped one.

Bhrescobar-- Do you know what type of bearings those .46 cubic inch singles have? Ball, caged roller or needle type? Are they main crankshaft bearings or rod journal bearings or both? Two stroke or 4 stroke? What types of models? Strictly engines for demonstration (a growing hobby subculture in the USA) or for propelling or driving something else, a scale model or to do some kind of useful task?

Ed Weldon

Theoretically a babbitted journal bearing has an infinite life. Theoretically a roller bearing always has a limited life due to fatigue damage, especially under an alternating load as in an engine. That fatigue life is actually not all that long either.

So, cheaper, long life, better contamination resistance, all make a journal bearing the best choice. For machines in critical service like turbines and large gas compressors we always use journal bearings.

According to Wikipedia "Compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system." It seems these work the same as an oil filled journal bearing but use air as the fluid.

Gas turbines for model aircraft run rolling component bearings, often made in ceramics, with 120,000 rpm quite normal. A little oil is bled through them for cooling and lubrication, but too much makes them overheat. The life of the bearings is not long in hours.

Of course the simple shape of gas turbine components makes rolling component bearings easy to install, unlike multicylinder piston engines.

Some additional benefits associated with Journal Bearing not mentioned so far:

• As speed of the shaft increases there is a crossover point where the friction of the Journal bearing is less than that of Ball, Roller, and Needle bearings.
• Journal bearings can be partial shaft diameter whereas Ball, Roller, and Needle bearings must be full shaft diameter.
• Journal bearings has a greater capacity to withstand shock.

Others have mentioned the advantages of soft metal shell bearings.

In modern engines the bearing theoretically will never touch the crank due to a film of pressurised oil.

However 2 stroke engines which cannot hold free oil in the crankcase have needle bearings.

I would never expect a 2 stroke bottom end outlast a oil pump fed shell big end.

Greetings.

I was about 12 years old when I watched my dad pour new babbit bearings in the transmission of our 17 foot speedboat. It didn't take that long and we were back in business and no vibration. Some babbit, some oakum, a torch, and a little know how.

Unless it has changed all of the generators in the dams on the Columbia River run on babbit bearings. The bearings are laid out like slices in a pizza. They can pour just one slice of the defective area and be back in business as relates an olde engineer who worked the dams.

Old Model T Fords had babbit bearings and owners used bacon rind to slip in when a knock was noticed. As soon as possible then the engine was taken down and new babbit bearings poured. I was told by my dad that it usually was the front bearing that usually went out first.

cheaper...but sufficient to provide the hours of service needed before engine wearout.

Hi,

It looks like this one has run its course,you now have a wide overview on a variety of bearing issues.

I would just like to add that as the plant manager responsible for a base load CHP installation I recently inspected the internals of 3Nr 1500 rpm 1050kW (Vee20 !!)turbo charged gas engines each of which had completed 60,000hours of virtually continuous operation.

The journals and bearing surfaces were damage free and still within manufacturers tolerances and no doubt could have continued for longer; the key to this excellent outcome is due to the initial design,the manufacturing accuracy,oil chemistry and as part of the supporting maintenance service the on-going monitoring of the oil quality.

I reckon that 5,400,000,000 revolutions carrying upwards of 90% full load is justification for keeping the low cost,simple plain bearing arrangement for the foreseeable future.

Happy motoring!

When my company bought a new 400 hp screw type air compressor we were rather surprised to learn that it had babbit bearings. I can't remember the oil pressure but it must have been very high.

Nah probably not. No more than 20 Psi anyway. Probably around 15.

Lots of screw compressors have journal bearings. Especially the big ones in oil field service.