GEM is, of course, required reading for anyone involved in the stationary engine hobby, so you can imagine that every month, the latest issue is discussed on the stationary engine mailing list. The recent two-part article by Craig Prucha, about his extreme restorations, generated much interest.

* What do you all think about Criag's method of drilling, tapping, and using brass screws in order to align the crankshaft and get the proper standoff, and then pour the babbitt? Sounded good to me, as a relative newcomer to the hobby. For those who didn't read the article, he left the brass screws in.

* It is the same method I was taught by a man who worked in the elevator business all his life. They poured many bearings in place using this method. A very knowledgeable man! The best advice he gave me when I first started to pour a bearing was "what have you got to loose- if it does not pour right, melt it out and pour again!"

* I'd think this method would make it a bit harder to use a bearing scraper if you wanted to later on. But I guess that might be a problem for the next owner and not a problem you'll face.

* Clever idea in my opinion. I can't see any problems with this method. Good original thinking.

* Two weeks ago I poured babbit on a trip hammer crankshaft (first time of doing this) and the way I set my distance was to take an old leather belt, cut two pieces, one for each main with the leather longways (¼" wide by ¾long) resting on the bottom of the main and sat the shaft in place (the shaft held the leather down). After I had smoked it up, I made a dam on both sides of each main, heated the main casting pretty warm while keeping the babbit hot, then poured the babbit, one at a time . The leather is still in place and will hold some of the oil and if I ever need to redo the babbit , it comes out real easy.
Quick, simple and easy.

A discussion doesn't go very far unless you have some disagreement. And we at the stationary engine list are proud of our longstanding ability to disagree. In this case, the voice of dissent was from an Australian contributor.

* The brass screws will rip the crankshaft journals to shreds. Brass is infinitely harder that the babbitt metal and will react/respond/perform quite differently to the lubricant. The leather strip method sounds reasonable if you don't want to go to an adjustable frame type setup.

* I would trust Craig's knowledge/workmanship 100%. Perhaps the brass in OZ is harder than that which we have here in the USA, or perhaps the steel from which we make our cranks is harder than that used Down Under. In any event, the bearings on my 15HP IHC are brass and have done no damage to the crank during the past 90 years. Additionally, most rod bearings on oil field engines produced here in the USA (90-100 years ago) were simply brass "blocks" that have been machined to fit the crank - thus the name "brasses." That's what was on the Tillinghast half-breed oilfield featured in December 2001 GEM. (John Fankhauser modified a set of brasses to fit her.) 100 plus years of wear and no perceptible damage to Tillie's crank! I also have a 2HP Jaeger in my shop right now that used brass pins (perhaps ¼") to insure that the bearings didn't
spin - again, no perceptible damage to the crank.

* I would also tend to disagree with your thoughts on this. While brass is considerably harder than babbitt, you must take into account the bearing surface area. You might have only 1/16 of a square inch (or less more than likely) per brass screw of surface area touching the crankshaft (if the screw head totalled ¼"). You would possibly have 24 square inches (for say a 2½" crankshaft with a 6"wide journal) of babbitt material touching the same crankshaft. The wear differential would be so minute that I think you would not see any significant wear at the screw area.
Leather sounds OK and I think would work fine for our old hunks of iron. But, if you have a piece (or pieces) of leather 1" wide and say 2" total in length to support the crankshaft, on the scenario I mention above, you are going to lose close to 10% of your bearing surface area. For the old slow running engines, I don't think it matters either way.

* I may try the brass screw method on my 3HP Galloway. I had never gave scraping any thought, but I guess one could always centerpunch and drill the head off or use a small enough screw and literally twist the head off.

* If you carefully coated the screw with something like Never-Seize, you could possibly back it out once the bearing is poured. Don't think there would really be a need to.

* That's kinda what I was thinking. But if you drilled/twisted the screw head off and left the shank, you would be certain that the babbitt wouldn't "spin."
One thing with the screw idea. Small vernier adjustments could be made prior to pouring to assure good alignment, proper babbitt thickness, etc.

* It seems to me that the brass is harder then the babbitt BUT the brass is softer then the crank shaft and the brass is a much smaller area then the babbitt. Therefore the babbitt will continue to do most of the work of supporting the crank and the brass will be worn away at the same rate as the babbitt with the rate being controlled by the babbitt.
Put another way, the crank can't get to more brass to wear it until the babbitt around it is worn away, and the brass is to small to support the crank without the surrounding babbitt.

* The bearings in my 2HP Chapman are indeed brass or similar metal; they are a split bushing, not babbitt. There was very little crankshaft wear, but the bearings themselves were worn quite a bit. I simply slid shimstock around the bearings when I put them back in, compressing them a bit and tightening this up.
The 7HP has babbitt bearing halves. Big ones.

* Doing a quick mental inventory of our stable, we have two Allens (Scotch), one Commercial (American), one Goold (Canadian), and one Lorenz (Czechoslovakian) that use brass mains and rod bearings.
Of the engines in our garage using brass, it's interesting to note that 100% of the American engines run perfectly. Even 100% of the Czechoslovakian and Canadian engines run nicely!
But only fifty percent of the engines with brass mains from Scotland run. That's a fifty percent failure rate! It's no wonder that they pawned their engines off on the unsuspecting Australians.
So to answer the question, it's perfectly fine to use brass in your bearings, as long as you avoid that which came from the brass mines of Scotland.

* I wonder if the "brasses" might actually have been bronze. I've been told that bronze makes a much better bearing than brass. How does one tell the difference?

* I don't have a clue. The way I keep the two separate is to buy brass and mark it as such and specify bronze when I order and mark it as such.
The brass and bronze I buy machine differently, I can tell that much; but, there's a wide variety of alloy compositions in both. It's hard to generalize the characteristics of the two.

* Thanks for your comments back on my experiences with brass and babbitt. I suspect that most of the 'brass' bearings are in fact bronze. It's the proportion of zinc to copper to tin that makes all of the difference.
Anyway, I quite agree that bronze (or brass) makes a great bearing surface. My comments re brass screws came from direct observation of a crankshaft that had been very badly scored by the brass dowell pins that located the brass-backed babbitt-lined shells. My memory fails to recall the make but I believe that it was an American 6 cylinder petrol engine of about the 1930's and it was out of a dragline or small shovel. The brass dowells had a step in their diameter, with the larger diameter locating in the main bearing tunnel in the crankcase and the smaller diameter locating the bearing shell. This was used instead of the more common tang device. On two of the main bearings, the dowells had worked through the brass shell and had scored the crank. Needless to say, the brass shells had also worked their way in the tunnel to the point where the tunnel needed to be line bored to true it up. A new set of brass shells were made, with oversize diameters to suit the new tunnel diameter. These shells were then babbitted and bored to match the rebuilt crankshaft. New brass dowells were used but this time they were threaded into the bearing tunnels, with their tops well below flush with the bearing surfaces in the fitted shells.
The use of brass screws to locate the crank is a good fix but I would not contemplate it if the engine was going to be put to serious use.

* You made a really good point. The way I look at it is that if you take the amount of horsepower and divide it out by the surface area of the bearing on both our old engines and the 6 cylinder engine that you worked on, you will find that our old gas engine has a lot less "power" or "load" per square inch than the more modern engine. True, the slower the speed the larger the shaft has to be to handle the same horsepower, but I think one
of the big things in modern engine design was less material doing more work. I see your point; the softer babbitt would wear away until the shaft was actually being carried by the screws. Now, instead of the bearing load being taken by the surface area occupied by babbitt, it would be taken by the screws. This would really localize the load over a very small area of the shaft, and could cut the shaft. Once the shaft is cut, it is a place where a fracture could start. So, in theory I suppose it COULD be inviting a disaster, but in practicality, the screws will just wear and the shaft will seat back down on the babbitt.
If I were doing it, I might take the die grinder with a carbide burr and carefully grind the screw down below the surface of the babbitt, leaving a little divot which would just fill with oil or grease. Chances are I would just run it and after it had run a while, take a cap off and see how it looked.
While many engines did use brass or bronze bearing boxes, babbitt eventually won out because it was cheap and easy to replace and it was softer and would do less damage to the journal if it ran dry. My Corliss engine has brasses on the crankpin, but they were babbitt lined from the factory. Babbitt does run a little cooler and more freely.
Ultimately, if Craig endorses an idea, I don't question it because he is ten times the machinist, restorer and collector that I will ever be! The method he uses is the exact way that our millwrights at the paper mill I work at support lineshafting when they pour new bearings.

* Babbitt is softer than brass and will allow dirt and other impurities to sink in to it that would not be able to do so in a harder material such as brass. The brass will hold the junk against the crank shaft and score it where babbitt is much less likely to do that.
When you fill your grease cups on any engine, brass bearings or babbitt, be sure to keep the grease clean. Doubly so with brass ONES.

* If you'll all open your Machinery's Handbooks to the chapter titled "Non-Ferrous Alloys" you'll see that both brass and bronze can be used in some bearing applications. Usually a bronze alloy will be better suited for a heavy duty bearing applications. You'll also see that there are MANY different standards that are best for very specific purposes.
Opening the SAE Handbook reveals similar applications. It states that the nomenclature for these alloys is sometimes blurred. Generally speaking, brass is a copper-zinc alloy and bronze is copper-tin. Examining the recipes, however, shows that this is not always the case; metals are usually in different proportions and tend to cloud the accepted rules.
The bottom line is that any statement using the terms "brass" or "bronze" is a generalization that should probably be clarified.

As is usually the case with old engines, there are no hard and fast rules. Manufacturers were constantly "borrowing" ideas from each other and developing new ideas of their own - much like the car designers of today. Through discussions such as this we can learn ways of keeping the old engines running for future generations.

On a side note, over the past week there has been some readjustment of the balance of iron from one side of the Atlantic to another. The Baker Monitor and pumpjack my husband gave me at Portland finally arrived in England, along with a Maytag twin and a small R&V purchased at the big R&V show in September. In return, a small two-stroke lawn mower engine headed west. Hopefully, you'll be able to read about these engines in future editions of GEM.

Site Index


Articles Index



©FBI 2004