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Repairing Crankshafts

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This morning dawned bright and sunny; a clear-blue, cloudless sky and just a hint of frost. According to the weather man, it's just a pause between two lots of bad weather, but it couldn't occur at a better time because today is the last show of the season.

The show itself is simply an afternoon at the Victorian-era steam sewage pumping station in our local town, but it's a good excuse to get the engines out one last time. Four beam engines sit inside the station, one of which will be in steam for the afternoon while the stationary engines run outside.

It gets dark by around 3:30 p.m., so people usually bring lighting displays, either engine-powered or oil and acetylene lamps. A brass band sets up at the top of the engine house between the beams and plays Christmas carols, and the transport museum, which is housed at the site, gets out toys to drive or ride around.

Before we turn our attention to the warm engine shows of summer, plenty of time still remains for restoration and repair projects. The discussion here began with a report from a list member following his visit to the Jeremiah O'Brien Liberty Ship in San Francisco, Calif., and observations about the method of assembly of the crankshaft in the ship's engine.

And so, on to the discussion that attracted my attention this month on the ATIS Stationary Engine Mailing List.

Inspecting the ship's engine, we decided its crankshaft was a built-up assembly, probably with shrink-fitting of the journals. I recently picked up a copy of Machine Construction & Drawing, a 1930s book by Frank Castle. It has drawings of line shaftings, fast/loose pulleys, bearings and engines.

One item that caught my eye was a drawing of a ship's crankshaft: the journal diameter was 15-inch with a width across the web of 29 inches. Not quite as big as the Liberty ship, but almost identical in construction, with the journal shrunk into the webs and a dowel pin fitted in a hole drilled exactly on the joint to stop any rotation. Another, larger crankshaft is shown in another drawing with journals of 26 inches in diameter but with slightly different methods of construction.

This was a practical method for making up a replacement shaft, but has anyone used this method to produce a spare crankshaft for a stationary engine?

Ronaldson-Tippett built its Austral Oil Engines with a fabricated crankshaft. It is made of five pieces pressed together and is the only flaw in the engine's construction: Some assemblies slip, the flywheels go out of line, and you have an unbalanced engine.

How about welding up a crankshaft bearing surface that is rusted and pitted? I need to fix a crank on my current project, and I think I should be able to weld it and have it turned. Keeping her straight would be the trick.

An instructor at our junior college told me that any time a crankshaft is welded it must be straightened before grinding down the journals or mains. He uses a hydraulic press to get the crankshaft in alignment.

Welding a crankshaft is easily done with a submerged arc machine. If you want to do it yourself, you have to first grind the surfaces to be welded to eliminate any contaminates or hardening. Then you have a choice of wave welding or rotary. Wave welding is easiest if you don't have access to a lathe or turntable (you need to rotate the crank slowly to do rotary welding). Then you heat the journal up and use the proper rod to build up the journal so that all of it is higher than needed. Once the welding is done, let it cool slowly, then straighten it. (If you have a couple of V-blocks and a dial indicator you can do it yourself.) You can use a press, but the pros use a big hammer and a brass drift. Once the crankshaft is straight you grind the journals to the correct size. I've done a couple and had good results.

I've had a few bad crankshafts, but I didn't have them built up and ground. Instead, I had one ground true and then had a brass insert made for the brass rod journal. The other had a poured bearing, and I simply had a new bearing poured. If you take more than 0.10-inch off to smooth it up, you may have to go the build-up route, as you are beginning to lose some strength in the journal.

I had one of my crankshafts metal sprayed. The process brought it back to size, and it machined and stayed true. Before it was sprayed, it was rough-cut in a lathe to give a good 'key' for the metal spray. This also left a good depth of spray metal after machining.

Spray metal sounds intriguing, but a fellow at one of our machine shops says he doesn't trust it to hold. I have seen sprayed rebuilt water pump shafts fail in a few hours. Another dealership told us they had seen the same thing and quit using rebuilt shafts because the metal spray didn't have a good bond.

Metal spraying for crankshafts was used extensively in the 1940s and onwards in the United Kingdom, and was used for many years by London Transport when reconditioning diesel bus engines.

The key, if you'll excuse the pun, is ensuring a good bond between the new metal and the old surface, and to this end it is necessary to take off the old surface before spraying on new metal.

As for welding, I have an old Amanco crankshaft that has been welded all over the big-end surface. The shaft is now well out of true, so apart from the cost of getting the bearing ground back, the shaft has to be straightened again.

I have a friend who builds models. He builds his crankshafts starting with a full-length main-shaft, slides the webs to the correct position, fits the crank pin, and then silver-solders it all together. He then saws the main shaft just inside the webs. This method maintains perfect main-shaft alignment for him. With large enough webs and sufficient shrink fit, it would seem this method should work nicely for replacement crankshafts.

There's a company in North Carolina that is the official repair center for John Deere crankshafts. They preheat the crankshaft, submerge arc weld it in a lathe (a neat automatic welding process), and then rough turn and final grind it to restore the crankshaft. A hit-and-miss crankshaft should be a piece of cake for them.

In this hobby, anything is possible. It all depends on your available knowledge, resources and, quite frequently, that all-important resource - hard cash! Well, nobody ever said our obsession for preserving engines of the past for future generations to appreciate would be easy!

And in the spirit of seeing some of those future generations enjoy the power of the past, I'm going to put on a few more layers of clothing and head off for the pumping station! From the worldwide contributors of the Stationary Engine Mailing List, we wish a Happy New Year to the readers of GEM!

Engine enthusiast Helen French lives in Leicester, England. Contact her via e-mail at: You can join the Stationary Engine List on the Internet at: