[size=6][/size=10]Just curious: how much trouble, time, skill, and expense would it take to convert a largish operating steam locomotive from friction bearing rods to roller bearing rods? Are the parts readily available for common types, or would it be strictly a custom maching job?
Similar question, but what about converting main axle friction bearings to roller bearings?
Thanks!
Dave
Dave,
A question to help you answer your own question…
Why are the main crankshaft bearings and the piston rod bearings in automotive engines still hardened and sintered bronze?
Because the reciprocating forces would destroy a ballbearing or roller bearing.
The actual rollers, or bearing might be able to take it, but the race it rides in would scar.
Think about the force being put upon the rods in your car’s engine, thousands of time a minute…then carry that across to the immense weight and size of the side rods on a locomotive…it would shatter a roller bearing.
The axle bearings on a lot of steam locomotives were roller bearings, all they have to do is support the weight of the locomotive, the suspension absorbs most of the shock from the rails, and you want some play in wheel bearings.
Timken, and National Bearing made, and Timken still makes axle bearings for locomotives and rail cars.
The tolerances (clearances between the rod and whatever it rides on), and the clearance between the hole in the rod and the outer bearing surface is much, much closer or tighter with a friction bearing than you could ever get with a roller bearing, there is only enough “space” between the two for a thin layer of lubricant, something like a few microns, which the rod “floats” on, it never makes true contact with the bearing surface unless you fail the keep it lubed.
You cant make a roller bearing like that, there has to be enough play in the rollers to allow the one next to it to rotate or they bind against each other, which is way more play than a friction bearing has.
Last, note that almost all large engines, or any large machine that has rotating parts, like drive shafts, propeller shafts, turbines, connecting rods, piston rods, crankshafts all use “friction bearings” or block bearings for the simple reason that the tolerances needs can not be achieved with roller or ball bearings.
And not all friction bear
You would need to be able to make the new rods and and crank pins and probably new axles. This would require a big machine shop with very substantial lathes and milling machines. The roller bearings themselves would be either special orders or bearings at the upper limit of normal production sizes.
The bearings would need to be able to take misalignment. SKF bearings had spherical section outer races and barrel shaped rollers to allow this.
The rods used were of a different design, with much larger ends to take the roller bearings.
For roller main bearings, you might need new axles, but at the very least, you would have to press the wheels off, machine the bearing surfaces, fit the roller bearings, the fit the wheels. You would also have to accurately “quarter” the wheels, putting the cranks at exactly 90 degrees.
Think about costs in the order of half a million dollars. You might get change, but you might not.
And as for finding people with the skill, ask Union Pacific’s steam maintenance team. They haven’t had to do all of that yet, but I guess they could.
M636C
Actually, the use of roller bearings on main and connecting rods was quite common on the last generation of steam locomotives.
The following is a quote from “Norfolk and Western Steam (the last 25 years)” by Ron Rosenberg, published in 1973 by Quadrant Press, Inc.
“…the J’s were designed with roller bearings on all loco and tender axles, as well as on the wrist and crank pins and valve gear. Mechanical lubricators were specified to reach 220 points and operate 1300 without replenishment. On extended runs only the roller bearings on crank and wrist pins needed attention at 500 mile intervals. The new locomotives went an average of 238,000 miles before classified repairs became necessary, and drew assingments approximating 15,000 miles per month…”
The last production run of N&W clas A 2-6-6-4’s was also equiped with roller bearings on crank and wrist pins and also set records for performance and reliability.
The first steam engine to have then was the Timken “four aces” #1111. I believe it was used on one of the Great Northern silk trains for a long time. The differences in rods are quite apparent if you look at a picture of the N&W J class side rods. In general the head where the crank pin is inserted is much larger than a standard rod to accomodate the roller beraing (not a ball bearing). This has no effect on clearance as the rod is not thicker front to back just bigger in circumference to accomadate the bearing. The PRR T-1 had this same arrangement. It is interesting to note that the railroads almost universally thought roller bearings were a good idea for passenger equipment but were a waste of time for freight cars and engines and would offer no benefit. One more time they didn;t get the picture.
You can get very tight tolerances – zero lash – with roller bearings, depending on the bearing type and assembly. Most commonly done with paired tapered roller bearings in a single bearing assembly, but also done (e.g. aircraft gas turbines) with single tapered roller bearings at distant locations on a shaft, with clearances adjusted with shims. Very carefully.
That being said, however, what’s the point? As has been noted, if you have good friction bearings, the cost to change over would be very high, and the payback (particularly for an excursion engine) would be a very long time away. A properly designed and maintained friction bearing works just fine!
Why do roller-bearing axles require accurate quartering?
You seem to be saying the 1111 had roller bearing rods. It didn’t, did it?
The quartering isn’t a function of the roller bearings, it’s a necessity of reassembly of the wheelset when one wheel is removed from the axle for any reason. For servicing or replacing the standard friction bearings, disassembly of the wheelset isn’t necessary, it is for placing or replacing roller bearings on the axle.
Dave,
For what its worth,T&P 610 was fitted w/Timken bearings in about 1949-50 and when they moved it to restore it to pull the Freedom Train thru Tx.They were still in good shape and unless they were replaced by The Southern RR they are still in use…I say all this to tell you ,might check the internet to find out the piticulars on what they had to do to change them…Good hunting,Danny
Roller bearings will last almost forever, provided three things: they are properly lubricated, they are never overloaded, and never subject to heavy impact. Violate any of those conditions, and they can and do fail catastrophically, and sometimes very rapidly. In an aircraft engine, a lubrication failure can destroy a bearing (with very interesting consequences) in a matter of minutes. On railroad cars (or engines), a bearing going bad can go from no noticeable problem to no noticeable bearing in a few tens of miles. But properly maintained they’ll go forever. A friction bearing, on the other hand, doesn’t fail as catastrophically – they tend to take their time about it, and give more warning. But they do have more friction (particularly at rest)… you takes your choice.
To give you an idea of the effort involved, UP is in the process of replacing the crank pins on 3985 and they expect to have the locomotive out of service for about a year to do it.
dd
Timken 1111 had conventional rods both when new and as NP2626. It had roller bearing axle bearings throughout.
I think NYC 4-6-4 5344 “Commodore Vanderbilt” would be an early user of roller bearing rods when streamlined in 1934 (?) or so.
M636C
Might be mistaken here, but I seem to recall that the Tennessee Valley Rail Museum shops were doing a boom business rebuilding drivers and rods for museums/ excursion steamers across the country. They might have the answers you are looking for, and I would suspect they also are a little less busy (and costly) than the UP.
Erik
Thanks everyone for the input.
Long and the short of it is that there has been some discussion of roller bearing retrofits, for rods and/or axles, on a recently-restored medium-large loco that has had some rod bearing difficulties. Although I have a mechanical engineering background, I suspect that this issue is so much a function of experiential considerations that I am not remotely qualified to address the practicability, much less the pros and cons, of such a switch, but was only trying to get thoughts on whether it is a realistic notion.
You’ve given me some good food for thought.
Dave
Quartering has nothing to do with the type of bearings used. Quartering is done so that both cylinders won’t be at “dead center” at the same time. Accuracy is important but consistency is much more important. All of the axels have to be quartered exactly the same. That is, if one is 90.5 degrees and the other is 90 degrees and a third axel is at 89.5 degrees you are going to have a failure (perhaps a catastrophic failure) of one or more side rods since the distance between the crankpins will be constantly changing. I don’t want to be anywere near when that happens.
AHA! Only just returning to this post, to find that the issue involves “some rod-bearing difficulties” on a recently-restored locomotive. That may be – imho, almost certainly is – something unrelated to what roller bearings would address.
Dave, since you don’t provide e-mail, this has to start in a forum post – exactly what are the ‘rod-bearing difficulties’ you’re having? If one bearing is consistently running hot, even after careful machining and checking, you likely have either a quartering problem or an axle-alignment problem (presuming you’ve already checked the frame for trueness in all planes, how are your wedges set?)
Roller bearings would be MORE, not less, a liability in such a situation. Note that when a typical sleeve bearing wears, the locomotive can still be run (although with that typical ‘clanking’ sound) whereas roller-bearing failure means immediate and expensive repair. And the permissible error in quartering for rollers is very small – I don’t have figures immediately at hand, but seem to remember numbers involving tolerances measured in thousandths, which measured as arc at crankpin center would require very careful – VERY careful – attention to accurate process during quartering! (As mentioned, it’s the relative precision of quartering for the driver pairs, not the exactness of 90-degree quartering per se, that controls things here).
Roller-bearing retrofits on driver axles are almost certainly not going to be cost-effective, not only for the reason already given (the need to remove at least one driver to R&R the bearings, or alternatively provide split races and cages) but also because the required box will likely be of substantially larger outside dimension than what you’re already running with plain bearings – you might be able to machine out the pedestals (and incidentally fit something like self-adjusting wedges if you don’t have them) but that’s a zany solution unless you already have access to all the required tools and skilled peopl
You know, I agree with what Overmod implied here, without saying it. We’re friendlies, at least most of us, and we might be more help if we knew more exactly what we were dealing with in the way of a problem…