Railway Preservation News

Turning Crankpins
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Author:  hadder [ Wed Aug 23, 2017 4:35 pm ]
Post subject:  Turning Crankpins

Our locomotive 29 developed rust on the crankpins while sitting outside in storage for 8 years. It has made several successful trips since then and the rust wasn't even detected until recently, when an overheated crown brass necessitated removal of the rods and led to a more thorough examination. The pins have been polished with sandpaper to clean up the rough edges, but the pits remain.

We still have the quartering machine, so turning the crankpins is definitely within our realm of abilities. However, I was wondering if anyone had come up with a method for resurfacing the pins without removal of the drivers from the locomotive? I'm trying to envision some sort of portable tool and associated jib assembly to mount on the hub.....

Eric Hadder
Grand Canyon Railway

Author:  Dave [ Wed Aug 23, 2017 5:14 pm ]
Post subject:  Re: Turning Crankpins

Portable crankpin lathes which do just that - powered by air motors or electrically - have been around for decades. Few remain, perhaps somebody who has one can help you out. I used one many years ago and after some finagling got a pretty good job out of it.

Author:  John Risley [ Wed Aug 23, 2017 5:54 pm ]
Post subject:  Re: Turning Crankpins

Heard them referenced as "journal squirrel". Industry has used them in paper mills, roll journals ect. Saw one being used to resurface a smaller axle on semi trailer with same principle. Not sure where to rend or borrow one though. MC former CMO used on to clean up crank pin on smaller 2-8-2 a while back probably 10-15 years ago. Sure someone will come along with the full info. Might have to rent the machine which is never cheap. Regards, John.

Author:  Pegasuspinto [ Wed Aug 23, 2017 8:26 pm ]
Post subject:  Re: Turning Crankpins

We have one that was 'shop built' at the Arkansas Railroad Museum. It was made for Cotton Belt 819 so I don't know what it would take to adapt for another engine. Probably weighs 200 pounds.

Author:  dinwitty [ Wed Aug 23, 2017 9:27 pm ]
Post subject:  Re: Turning Crankpins

I think they did some lathing on 765 on its first restoration, someone brought a measurement tool and spun it on all the crankpins, I don't know if they used a specialized lathing machine, but the work on that engine was frugal, inspiration on the fly to solve problems. I am not sure if minor pitting is an issue, well lubing may keep the issue minimal. Turning it may reduce the diameter needing a slightly larger brass bearing. Would some metal re-surfacing work? Otherwise maybe manufacturing a new pin an answer, but thats a larger project than needed for this, just a thought.

Author:  b. barry [ Wed Aug 23, 2017 9:59 pm ]
Post subject:  Re: Turning Crankpins

A portable crankpin lathe was built at the Wiscasset Waterville and Farmington Railway museum to work on no. 9's crankpins during the locomotive's restoration.

Video of a crankpin being turned.


Some pictures of the portable lathe.







Author:  Overmod [ Thu Aug 24, 2017 7:49 am ]
Post subject:  Re: Turning Crankpins

Can you provide a picture of the pitting?

There have been discussions here about the remediation of pitting vs. turning journals with necessary brass replacement. If you use a small tool to open up and smooth some kinds of pitting, the effect on reduction of effective bearing area can be relatively slight, the hydrodynamic lube film even under peak thrust is maintained without starvation, and the pits constitute a kind of additional lubricant reservoir. It may also be possible to fill some pits with material that is not nominally 'load-bearing' but that keeps lubricant from displacing into the former pits and starving the tribology. (That is the real point of those epoxy compounds that are peddled for remediating pitted shafts of some kinds). My own vaguely conceived idea would be to use some type of braze to fill the pits, which would have some bearing strength as well as assuring lube integrity but would not involve as much heat and associated stresses as fusion welding.

Are there fabrication drawings of the WW&F machine? Looks to me like the result of some very careful thinking about what is required for this particular task.

Author:  Aarne H. Frobom [ Thu Aug 24, 2017 9:47 am ]
Post subject:  Re: Turning Crankpins

When we found the engine on display at MSU, Pere Marquette 1225 had oval crankpins, especially the mains. The Southern Railway lent us a portable crankpin lathe. This was rigged onto the face of the drivers, taking extreme care to preserve the throw, quarter, and squareness. This job was successful and the engine has operated well with new bronze bushings since then.

I presume the Southern's tool was auctioned off when the Irondale shop was closed, and I don't know who has it. It had the appearance of being part of a larger machine, maybe a quartering machine. They may have had more than one.

Aarne Frobom
Steam Railroading Institute
Owosso, Michigan

Author:  dinwitty [ Thu Aug 24, 2017 10:16 am ]
Post subject:  Re: Turning Crankpins

I would think any abhorations in the metal would get smoothed by normal operating, pit edges would smooth, even on new engines any roughness might smooth. It seems scrambling up a tool like above would be invaluable. Braze filling sounds like a good idea if thats the good direction, over time inspection may be needed if the filling peeled out.
If wear has cause an oblong shape turning would be needed.

Author:  hadder [ Thu Aug 24, 2017 10:44 am ]
Post subject:  Re: Turning Crankpins

Thanks for all the suggestions. Everyone has brought up good points.

I'm curious about the idea of filling the pits. One of my staff suggested this, but was thinking more along the lines of electroplating. My concern would be, even if you were able to get material to stick (the crankpins are of course impregnated with grease), wouldn't you need to then turn the pins back down again after the addition of new material to renew your bearing surface? And if so, other than maintaining the original diameter, what is gained if they have to be turned anyway?

BTW, the pins are still perfectly round. Not oblong at all.


Author:  Dave [ Thu Aug 24, 2017 11:31 am ]
Post subject:  Re: Turning Crankpins

I used a proprietary epoxy filler made for heavy load and low RPM shafts from Grainger or McMaster, can't recall which, for a similar situation. Small pits do in fact distribute grease as mentioned. Pits with sharp edges which do cause trouble can be smoothed with Time Saver lapping compound in service. Babbitt can be used to build up the bore of the bearing if you do take off much meat. Flap wheels in drill motors do a very nice job of creating general smoothness. A certain amount of noncondemnable out of roundedness is normal after time in service - be reasonable.

It isn't rocket science, your mileage will vary depending on the particulars of your situation, and it never has to be perfect, just good and practical for your purposes.

Author:  dinwitty [ Thu Aug 24, 2017 9:50 pm ]
Post subject:  Re: Turning Crankpins

Your crankpin is hardened metal. a heated metal replacement, make sure the placement is done extremley locally hot then maybe a major splash of water right after metaling. I think a brazing fill may be the best. Your engine most likely will not be operating in real hard core sessions like in its real railroad operations, the only concern I can think of if any pits start any cracking and I think thats a very minimal worry.

Author:  Dave [ Fri Aug 25, 2017 7:14 am ]
Post subject:  Re: Turning Crankpins

No it isn't.

Author:  DRS.GPBensman [ Fri Aug 25, 2017 10:32 am ]
Post subject:  Re: Turning Crankpins

CLIMAX Portable Machining & Welding Systems has available for rent any specialty machines
needed for steam locomotive maintenance.
They build, sell and rent portable lathes (crank pin turning), portable mills (true up frame pedestals, portable facing machines ( steam dome gasket area and cylinder head faces),
portable boring machines (bore cylinders, piston valves, and suspension holes in frames).
The last machine we rented was new and just put into the rental inventory.
They have their factory in Newburg, OR and a field service facility in Cincinnati, OH. and other cities.
They bought Bore-weld a couple years ago and now offer that capability with most of their machines. This would be for spring rigging holes in frames. But not for building up crank pins - that would result in an FRA Condemning defect.
Trueing your pins with your ex-Nickel Plate Road quartering machine would be the way to go; and would require replacement of the rod brass.

Author:  softwerkslex [ Fri Aug 25, 2017 10:37 am ]
Post subject:  Re: Turning Crankpins

What should someone do to avoid this? Should the rods be dropped and the pins greased before storage?

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