Stationary Engine List
Gas Engine Magazine is, of course, required reading for anyone involved in the stationary engine hobby, so it's no surprise the magazine gets discussed on the Stationary Engine Mailing List. The recent two-part article by Craig Prucha in the March and April 2004 issues about his extreme restoration generated a great deal of interest, as the following discussion shows.
What do you all think about Craig's method of drilling, tapping and using brass screws to align the crankshaft and get the proper standoff, and then pouring the babbitt? As a relative newcomer to the hobby this sounded good to me. For those who didn't read the article, he left the brass screws in place after the pour.
It's the same method a man who worked in the elevator business taught me. He poured many bearings using this method, and the best advice he gave me when I started to pour bearings was, 'What have you got to loose? If it doesn't pour right, melt it out and pour again!'
I think this method would make it harder to use a bearing scraper later on. But, I guess that's a problem for the next owner, and not a problem you'll face.
Two weeks ago, I poured babbitt on a trip hammer crankshaft (first time doing this). To set my distance, I took an old leather belt and cut two pieces, one for each main, with the leather lengthwise (1/4-inch wide by 3/4-inch long) 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 while keeping the babbitt hot, then poured babbitt one at a time. The leather's still in place and will hold some of the oil. If I ever need to redo the babbitt, it comes out easy.
A discussion doesn't go very far unless there's some disagreement. We at the Stationary Engine List are proud of our longstanding ability to disagree. In this case, the lone voice of dissent was from an Australian contributor.
The brass screws will rip the crankshaft journals to shreds. Brass is definitely harder than babbitt and will react/respond/ perform quite differently to the lubricant. The leather strip method sounds reasonable if you don't want an adjustable frame-type setup.
I trust Craig's knowledge and workmanship 100 percent. The bearings on my 15 HP 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 in the U.S. (90-100 years ago) were brass 'blocks' that have been machined to fit the crank, thus the name 'brasses.'
That's what was on the Tillinghast half-breed oil field featured in the December 2001 GEM. (John Fankhauser modified a set of brasses to fit it.) One hundred-plus years of wear and no perceptible damage to Tillie's crank! I also have a 2 HP Jaeger that used brass pins (perhaps 1/4-inch) to insure the bearings didn't spin -again, no damage to the crank.
I would 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) per brass screw of surface area touching the crankshaft (if the screw head totaled 1/4-inch). You would possibly have 24 square inches (for say a 2-1/2-inch crankshaft with a 6-inch-wide journal) of babbitt material touching the same crankshaft. The wear differential would be so minute that I think you wouldn't see any significant wear at the screw area.
Leather sounds okay and would work fine for our old hunks of iron. But, if you have a piece (or pieces) of leather 1-inch-wide and say 2 inches total in length to support the crankshaft, on the scenario I mention above, you're going to lose close to 10 percent of your bearing surface area.
For these old, slow-running engines, I don't think it matters either way.
That's kind of 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.'
Small vernier adjustments could be made prior to pouring to assure good alignment, proper babbitt thickness, etc.
The bearings in my 2 HP Chapman are indeed brass or similar metal, but they're 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.
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. I keep the two separate by buying brass and bronze and marking them 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 about characteristics of the two.
I suspect 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 regarding brass screws came from observing a crankshaft that had been very badly scored by the brass dowel pins that located the brass-backed babbitt-lined shells. My memory fails to recall the make, but I believe it was an American six-cylinder gasoline engine of about the 1930s, and it was out of a dragline or small shovel. The brass dowels had a step in their diameter, with the larger diameter located in the main bearing tunnel in the crankcase, and the smaller diameter located in the bearing shell. This was used instead of the more common tang device.
On two of the main bearings, the dowels had worked through the brass shell and scored the crank. Needless to say, the brass shells also had worked their way into 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 oversized diameters to suit the new tunnel diameter. These shells were then babbitted and bored to match the rebuilt crankshaft. New brass dowels 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 wouldn't if the engine were going to be put to serious use.
As is usually the case with old engines, there are no hard-and-fast rules. Manufacturers constantly 'borrowed' ideas from each other and developed new ideas of their own - much like car designers today. Through discussions such as this, we can learn ways of keeping 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 pump jack 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.
Engine enthusiast Helen French lives in Leicester, England. Contact her via e-mail at: Helen@insulate.co.uk You can join the Stationary Engine List on the Internet at: www.atis.net