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Rebuild of an old steam engine & Method for making split bronze bearings (aka "Brasses")

Joe Michaels

Diamond
Joined
Apr 3, 2004
Location
Shandaken, NY, USA
I have had to make some split "brasses" for the connecting rod on a small steam engine ( about 2" bore x 3" stroke). This engine has the classic 1860's design, and uses the strap & cotter design to hold the split brasses on the connecting rod. The history of this engine is unknown. I bought it almost 40 years ago from a man then about 90 years old. All he could tell me about the engine was that he thought it had been used to drive an exhibit of scaled-down machine tools at a World's Fair or similar. After that, he thought the engine passed into the hands of some kind of school or training program. This may be the case as many of the fasteners on the engine were changed out for slotted head (filister head or cheese head) screws. Whatever the history was, the engine had seen hard use and the main and rod bearings were shot and the crankshaft badly worn. No flywheel, only some smaller flat belt pulleys. Mismatched nuts on the studbolts on the steam chest cover.

After three household moves and sitting on a shelf for the past 30 years in our present home, I decided it was time to give the engine a rebuild. The reason is the governor which Lester Bowman so graciously sent me. This design of engine, ca 1860's, will be a good platform for the governor.

As I got into the engine, I discovered the main bearings were likely originally cast iron. These had a partial babbitting, maybe 1/32" of babbitting which dropped out of the bearings when I took them apart. The crankshaft was worn undersized from nominal diameter at the main journals, so the babbitting might have been done to repair the engine. The con rod brasses were totally wallowed out and had been filed at the split lines umpteen times. As I worked on this engine I discovered very little was any even or standard dimension. Journals all over the map for diameter, lengths of parts and center-to-center distances at odd decimals of an inch, and some things not quite parallel or square. This engine was built by file fitting and layout done using scriber, rule and dividers. Dimensions of things like the cylinder bore were probably checked with calipers rather than micrometer, so the bore is some odd decimal over 2". Some of the parts look to have been made by the cut-and-try method.

I have a 2" diameter bronze studbolt from a ca 1915 sluice gate on the NY City Kensico Reservoir. I've been hoarding that studbolt for 42 years. I decided to use it for new brasses for this steam engine project. The rod brasses presented a little challenge since they are split brasses with rounded ends to fit the straps. I knew if I made the brasses in one piece and cut them, even with a thin slitting saw, I'd have to deal with tiny shims to keep the brasses from moving in the straps. The answer was to make the brasses in two pieces to start with. The next question was how to hold the two pieces together for machining the outer dimensions and geometry to fit the straps, as well as drilling and reaming the holes for the crankpin journal and crosshead pin. I decided the quickest thing would be to make blanks for each half rod brass, and soft-solder them together. Machine them as one single piece & file the radius'd ends to fit the straps. After all machining was done, heat the brasses and melt the solder to separate the halves.

I tested the bronze studbolt to see if it took solder OK. I use lead-tin solder and "Nokorode" soldering paste and an ancient Prestolite air/acetylene torch for soft soldering. The bronze took solder and wetted nicely with 60-40 lead/tin solder. I milled out blanks about 0.015-0.030" oversized on all sides. I then tinned the faces at the split line with solder.
Once these faces were tinned, I filed the solder down to a thin layer, and then polished the soldered faces on emery cloth on the cast iron table of my Unisaw. I left a very thin film of solder on each face. I put soldering paste on these surfaces and clamped the halves together. I played the torch flame on the brasses until I saw tiny droplets of solder appear at the split joint. This gave me "one piece blanks" to machine. This allowed me to mill the blanks into assembled brasses as well as to file the radius'd ends. The big end brass was a bit more of a filing exercise as it is flanged. I had to file the radius inside the flanged sides of the brass.

I made new steel bearing pedestals ("Plummer Blocks") and new "brasses" for the main bearings. These were easy to do, no soldering needed. I assembled each main bearing with 0.006" of shims between the upper and lower halves. In that way, when I bore the bearings, I am boring with shims in place... and shims for some future generation to remove to 'key up' the mains if they wear over time.

The original crankshaft was made from a single piece of steel with some file work on the crank webs to blend the contours. I decided to make a new crankshaft, since the old one had way undersized main journals and an egg-shaped crankpin. I figured if I attempted to build up the worn journals with TIG, I'd have a pretzel of a crankshaft since the main journals had been turned a good 1/8" undersized. I had some harder steel plate from a railroad switch track part, so milled crankwebs from it. A Jeep axle shaft was softened in the coal boiler firebox and is being machined for the crankpin and main journals. It will go together with press fits and TIG welds, machined off flush. I got a curved spoke flywheel casting from Martin Pattern Works, so the engine will get a real flywheel.

The original piston is a three-part assembly. Two wide step-cut rings butt against each other and the piston heads. Rings are worn beyond any use. Cylinder just needs a honing. I will build up the piston heads with bronze brazing, machine a new midsection and fit new rings. I've never made step cut rings, so maybe will try it.

The steam chest cover has been butchered with a 1/2" NPT tapping thru it, not enough thickness for making up a tight pipe connection. Valve rod is wallowed in the steam chest boss. So, I am making a new steam chest and cover. Wider chest width to accomodate a tapping on top for mounting Lester's governor. New eccentric with a sheave for the governor belt.

Front cylinder head gets bored and fitted with a hard bronze neck bushing since it is wallowed out by the piston rod. Crosshead is a thing of beauty with some ornamental turning and filed curves, and is casehardened steel. It runs on cast soft bronze guides. The bronze guides are one piece castings with some graceful curves worked into them, polished to finish them. Unfortunately, they are worn beyond saving. It is obvious these guides were machined on a planer or shaper, in place on the engine's cast iron bed. Cuts were taken on the top, inside edge, and underside of each guide. I'll make new hard bronze guide bars and put them on turned steel support bushings.

Matching "period correct" nuts and bolts means making them to match what's original on the engine. Having hex collets for the lathe makes this job a lot easier. Having hoarded hard bronze studbolts and heavy hex nuts from that old sluice gate, I have material to make brasses and crosshead guide bars. Makes hoarding those studbolts and nuts for 42 years justified.

My plan for the engine is to put it on a shelf in my office and run it on compressed air. If I get through the engine rebuild, ultimately, it will drive a ceiling fan via belts and small diameter lineshafting in my office. Lester's governor has gotten a project underway that sat for 40 years prior. Getting to use filing and soft soldering and my eye and imagination will hopefully do justice to the old engine and provide a fitting place for showcasing Lester's governor.

I am sure plenty of people have used the soft-soldering trick to make split bearing brasses, but it seemed worth posting about it. I know if I were making split round brasses (such as for an old lathe headstock), I'd use this same trick. The difference would be that I'd soft-solder in a brass shim at the split line. This would give a true cylindrical bore and give a shimming allowance when the brasses were assembled in the headstock.
 
Kind of got me feeling guilty about the split bushings I made for my screw press, replacing the long failed babbitt. I made the bushing round, then split it. Would have been better to pre-split & solder then do all the machining. In the press now the two halves have .016 gaps, but are working fine and aren't spinning. Maybe I'll sell the job by saying the gaps allow the liquid grease running down from the press head to lubricate the journal... hmm faster I say it the better it sounds... :D
 
I have had to make some split "brasses" for the connecting rod on a small steam engine ( about 2" bore x 3" stroke). This engine has the classic 1860's design, and uses the strap & cotter design to hold the split brasses on the connecting rod. The history of this engine is unknown. I bought it almost 40 years ago from a man then about 90 years old. All he could tell me about the engine was that he thought it had been used to drive an exhibit of scaled-down machine tools at a World's Fair or similar. After that, he thought the engine passed into the hands of some kind of school or training program. This may be the case as many of the fasteners on the engine were changed out for slotted head (filister head or cheese head) screws. Whatever the history was, the engine had seen hard use and the main and rod bearings were shot and the crankshaft badly worn. No flywheel, only some smaller flat belt pulleys. Mismatched nuts on the studbolts on the steam chest cover.

After three household moves and sitting on a shelf for the past 30 years in our present home, I decided it was time to give the engine a rebuild. The reason is the governor which Lester Bowman so graciously sent me. This design of engine, ca 1860's, will be a good platform for the governor.

As I got into the engine, I discovered the main bearings were likely originally cast iron. These had a partial babbitting, maybe 1/32" of babbitting which dropped out of the bearings when I took them apart. The crankshaft was worn undersized from nominal diameter at the main journals, so the babbitting might have been done to repair the engine. The con rod brasses were totally wallowed out and had been filed at the split lines umpteen times. As I worked on this engine I discovered very little was any even or standard dimension. Journals all over the map for diameter, lengths of parts and center-to-center distances at odd decimals of an inch, and some things not quite parallel or square. This engine was built by file fitting and layout done using scriber, rule and dividers. Dimensions of things like the cylinder bore were probably checked with calipers rather than micrometer, so the bore is some odd decimal over 2". Some of the parts look to have been made by the cut-and-try method.

I have a 2" diameter bronze studbolt from a ca 1915 sluice gate on the NY City Kensico Reservoir. I've been hoarding that studbolt for 42 years. I decided to use it for new brasses for this steam engine project. The rod brasses presented a little challenge since they are split brasses with rounded ends to fit the straps. I knew if I made the brasses in one piece and cut them, even with a thin slitting saw, I'd have to deal with tiny shims to keep the brasses from moving in the straps. The answer was to make the brasses in two pieces to start with. The next question was how to hold the two pieces together for machining the outer dimensions and geometry to fit the straps, as well as drilling and reaming the holes for the crankpin journal and crosshead pin. I decided the quickest thing would be to make blanks for each half rod brass, and soft-solder them together. Machine them as one single piece & file the radius'd ends to fit the straps. After all machining was done, heat the brasses and melt the solder to separate the halves.

I tested the bronze studbolt to see if it took solder OK. I use lead-tin solder and "Nokorode" soldering paste and an ancient Prestolite air/acetylene torch for soft soldering. The bronze took solder and wetted nicely with 60-40 lead/tin solder. I milled out blanks about 0.015-0.030" oversized on all sides. I then tinned the faces at the split line with solder.
Once these faces were tinned, I filed the solder down to a thin layer, and then polished the soldered faces on emery cloth on the cast iron table of my Unisaw. I left a very thin film of solder on each face. I put soldering paste on these surfaces and clamped the halves together. I played the torch flame on the brasses until I saw tiny droplets of solder appear at the split joint. This gave me "one piece blanks" to machine. This allowed me to mill the blanks into assembled brasses as well as to file the radius'd ends. The big end brass was a bit more of a filing exercise as it is flanged. I had to file the radius inside the flanged sides of the brass.

I made new steel bearing pedestals ("Plummer Blocks") and new "brasses" for the main bearings. These were easy to do, no soldering needed. I assembled each main bearing with 0.006" of shims between the upper and lower halves. In that way, when I bore the bearings, I am boring with shims in place... and shims for some future generation to remove to 'key up' the mains if they wear over time.

The original crankshaft was made from a single piece of steel with some file work on the crank webs to blend the contours. I decided to make a new crankshaft, since the old one had way undersized main journals and an egg-shaped crankpin. I figured if I attempted to build up the worn journals with TIG, I'd have a pretzel of a crankshaft since the main journals had been turned a good 1/8" undersized. I had some harder steel plate from a railroad switch track part, so milled crankwebs from it. A Jeep axle shaft was softened in the coal boiler firebox and is being machined for the crankpin and main journals. It will go together with press fits and TIG welds, machined off flush. I got a curved spoke flywheel casting from Martin Pattern Works, so the engine will get a real flywheel.

The original piston is a three-part assembly. Two wide step-cut rings butt against each other and the piston heads. Rings are worn beyond any use. Cylinder just needs a honing. I will build up the piston heads with bronze brazing, machine a new midsection and fit new rings. I've never made step cut rings, so maybe will try it.

The steam chest cover has been butchered with a 1/2" NPT tapping thru it, not enough thickness for making up a tight pipe connection. Valve rod is wallowed in the steam chest boss. So, I am making a new steam chest and cover. Wider chest width to accomodate a tapping on top for mounting Lester's governor. New eccentric with a sheave for the governor belt.

Front cylinder head gets bored and fitted with a hard bronze neck bushing since it is wallowed out by the piston rod. Crosshead is a thing of beauty with some ornamental turning and filed curves, and is casehardened steel. It runs on cast soft bronze guides. The bronze guides are one piece castings with some graceful curves worked into them, polished to finish them. Unfortunately, they are worn beyond saving. It is obvious these guides were machined on a planer or shaper, in place on the engine's cast iron bed. Cuts were taken on the top, inside edge, and underside of each guide. I'll make new hard bronze guide bars and put them on turned steel support bushings.

Matching "period correct" nuts and bolts means making them to match what's original on the engine. Having hex collets for the lathe makes this job a lot easier. Having hoarded hard bronze studbolts and heavy hex nuts from that old sluice gate, I have material to make brasses and crosshead guide bars. Makes hoarding those studbolts and nuts for 42 years justified.

My plan for the engine is to put it on a shelf in my office and run it on compressed air. If I get through the engine rebuild, ultimately, it will drive a ceiling fan via belts and small diameter lineshafting in my office. Lester's governor has gotten a project underway that sat for 40 years prior. Getting to use filing and soft soldering and my eye and imagination will hopefully do justice to the old engine and provide a fitting place for showcasing Lester's governor.

I am sure plenty of people have used the soft-soldering trick to make split bearing brasses, but it seemed worth posting about it. I know if I were making split round brasses (such as for an old lathe headstock), I'd use this same trick. The difference would be that I'd soft-solder in a brass shim at the split line. This would give a true cylindrical bore and give a shimming allowance when the brasses were assembled in the headstock.
hi i read through your whole post( unusual for me) found it fascinating,, that's one hell of a project!!
 
In today's throw away world it's quite common to see two sets made and then cut one half out of each. I worked in a toolroom where we made blow molds. Standard practice was to CNC turn the parison rings, drill and counter bore the attachment holes on the CNC mill and then split them on the wire EDM discarding the undersized half. Very wasteful I prefer your method. Can't wait to see some pictures of the finished project.
 
I too would like to see pictures of this little steam engine whose description seems to indicate it was indeed a working engine and not a model. It seems Joe you are definitely improving it in terms of materials used in its construction. I especially like the plans for it after you've finished your renovation. I'm curious about the drive to the ceiling fan ?
 
Hello Lester:

As I got into working on this engine, I realized a few things:
-the engine has features of ca 1860's-1890's in its design. It uses a box style mainframe with the cylinder mounted from the bottom to the mainframe. Crosshead is
slotted and runs on cast bronze guides. Gib and strap rod ends, well made.

-aside from the connecting rod, the rest of the engine seems like it was built as cheaply as possible. It is almost as though the cylinder was landed on the box mainframe and then it was realized it would be impossible to get any screws to tie it to the bed on the steam chest side. Some roundhead 1/4 -20 screws hold the cylinder on the side without the steam chest. A couple of dowels were run up from inside the box mainframe into the cylinder under the steamchest to stake that
side of the cylinder.

-the main bearings are cast iron with about 1 /32" of babbitting in portions of them, and the crankshaft has main journals about 3/16" smaller in diameter than
the rest of the crankshaft, which is nominally 5/8" diameter. Two different main bearing and main journal diameters.

-I made a "dummy shaft' sized for the old main journals out of 1 1/4" CRS. I turned each end to fit the existing main bearings & cross drilled and reamed
the 1 1/4" diameter center section 0.500". I made a tramming tool threaded 1/2 -20, which fits snugly into the cylinder head where the piston rod would pass.
This let me set the distance from face of cylinder to centerline of crankshaft, existing. I then made a dummy shaft turned to fit the new main bearings ( 21/32"
or 0.656" diameter). This let me land the new bearing pedestals and main bearings on the engine frame on the original crankshaft centerline.

- Some work with another fixture, and I got the layout of the centers for the existing bearing mounting bolts. Transferred that to the bases of the new bearing
pedestals. Assembled the new main bearings and the
dummy shaft on the engine mainframe and things bound tight before I had the mounting bolts for the pedestals snugged. Some investigation revealed the top
surface of the box mainframe, which looked like it had been machined and polished (no tool marks visible) was not flat and the left and right hand top surfaces
were not even in the same plane for parallel. I should have read the clue: the old main bearings were as loose as could be, and their bases were mounted on
some kind of fiber gasketing doped to the mainframe ages ago. Scraped off that mess, did some filing on the frame and established that one side was flat
and in plane with the crosshead guides and parallel to the centerline of the crankshaft. The other side was running downhill towards the cylinder and had a bit of
a twist relative to the crankshaft centerline. I filed to get rid of the twist and dressed the surface flat. I then took measurements using temporary shims under the
new main bearing pedestal. This let me make a 'feathered shim". I took some 1/8" steel plate and set it up on my surface grinder. I stacked brass shim stock
(equal to the difference between high and low ends ) and the magnetic chuck held the steel just fine. This let me grind a tapered or feathered shim.

-the new main bearings are fitted to the engine bed. I also discovered the bolt centers for mounting the bearings were not in line, front to rear. I had drilled the
new main bearing pedestals with the mounting bolt holes in line front-to-rear. I chose one set of holes as reference and left them intact. I plugged the other holes
with threaded studs, silver brazed in place and filed off flush. I then located the new mounting holes and tapped them. My guess is things were laid out with
a wood rule and maybe a pair of dividers in a badly lit shop back when the engine was built.

-The 0.500" drill rod is doing the same thing a "tight wire" pulled thru the cylinder of a larger engine to establish
centerline would do. I am moving onto the crosshead guides next. Under the existing bronze guides, there was more gasket material doped to the engine frame.
I've got a design in mind for the crosshead guides that will keep the original crosshead since it is a real work of art. The original crosshead pin was worn
and the fit in the crosshead was wallowed out. I found an odd sized reamer about 0.010" over the nominal pin size, so reamed and fitted a pin made from O-1.

-the existing steam chest evidently had cracked across its bottom surface ages ago. It was patched with what looks like the old "Smooth-on" boiler and engine
water jacket repair cement. I am making a new steam chest, wider than the old one, to mount the governor you gave me.

-The cylinder is cast iron, nominally 2" x 3" stroke. In actuality, the bore is closer to 2.050" and the stroke measured 3.030". Again, this coming close to 2" x 3"
but being off a bit speaks of 'the good old days' when machinists worked off wooden rules in shops with bad lighting. Interestingly, the cylinder has the
steam passages drilled in rather than cored steam ways.

_I contemplated setting up the engine bed and taking a skim cut on the top surface but opted not to. The engine bed had no mounting feet no flange, nor mounting holes in it for mounting the engine. Someone in the past riveted steel flatbar to the bottom of the box frame to create some small mounting feet (take number 10
machine screws). Whoever built the engine apparently owned one tap: 1/4-20, sharp vee threads. They used some wierd size hex stock for the high head bolts.
-The eccentric seems to have had its own problems. In order to get it to line up with the valve rod, the eccentric is counterbored so a portion of it encased the
main bearing on that side of the engine. Seemed like an afterthought on the part of whomever was building the engine. Kind of 'make it up as we go along"
and "cut, try, file and keep at it until things work.... open up the clearances on the main bearings if things still bind..."

Initially, I was going to approach the engine rebuild with the attitude that I would leave things so the original parts could be put back to put the engine in orginal condition. I was mentally naming the engine "Hippocrates" after the Hippocratic oath physicians take to "do no harm" and out of respect for the doctors who
diagnosed, treated my cancer, and saved my life. As I got into the engine work, I've realized this engine was poorly designed from the git-go, had
varying workmanship ranging from fine work to sloppy work, was used hard, cobbed back together, and never really was right or what I'd expect for a 2" x 3"
working engine. My mental image of the engine changed from Hippocrates to "the sow's ear", as I am trying to make the proverbial silk purse from it. This
mental image changed again as I got further in and saw the gasket shims and smooth-on boiler cement. The expression: "treated like a red-headed step child"
seems to fit best. I am going to have to work at learning how to post pictures. Meanwhile, I am working my way through this engine.
 
Thanks for sharing with us Joe . It's great that your rebuilding & conserving a piece of history . It almost sounds like your making a engine from scratch . Just get a camera off a home security system & stream the work as its gettin done .
thanks again
animal
 
Silk purse from a sow's ear. Been a while since I've heard that one. I seem to go through a lot of turd polish myself. For pics, I just use a digital camera [no phone] and put the little card in this computer. It automatically downloads the new pics and puts them in the pictures file all by itself. Then it is only a matter of clicking on the picture icon here and opening the desired pic. Computer does the rest. Good thing too as I am as dumb as a bag of hammers when it comes to this stuff.
 








 
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