We at the Minnesota Transportation Museum in St. Paul are in the midst of a mechanical and cosmetic restoration of Northern Pacific Class Q3 4-6-2 No. 2156. While this is a cosmetic restoration, the locomotive needs to be able to be moved around the facility from time to time so we do need to do the job correctly. The rod bearings are pretty well shot (as much as 0.125" out of round) and need replacement.

We were able to recast the shoes and wedges with the original bronze which contained 14% lead, but it was nearly impossible to find a foundry that would handle that job due to the very stringent EPA lead reporting rules. No one wanted to "contaminate" their facility.

So the question is, what no-lead or very low lead bronze alloy should we use?

932 (SAE)660 has 1.5% lead and is widely cast. At least in the west not counting California.

Call Horizon Metals Inc. 1245 N. 200 W. Nephi UT PO Box 19 Phone: (435) 623-0963 Fax: (435) 623-1443

They have always done well by me.

CCdW

Chuck,
Magnolia Metals https://magnoliabronze.com/ is where we got a number of pieces for 1385..............mld

Another choice would be C-936. It has 11 to 13% lead. For bearings you would probably buy spun cast tubes and machine them to size. Again Magnolia metals would be a good source. Or you could order the finished bearings from Strassburg Railroad.

American Machinist Handbook Railroad section in 1930 editions call out 80-10-10 Bronze for rod bearings on steam Locomotives that a copper, tin, lead bronze also that is shown on various RR Specs. CDA 936 which is 79-83% copper, 6-8% Tin, 11-13% Lead is about the closest material available in centrifugal cast bar which a lot of people are using for rod brass.
Another suggestion in your situation if you have the skilled labor would be to bore out the old rod brass with at least 1/4" oversize of the pin and then tin bores and using high tin Babbitt pour a bearing then bore 1/64 oversize. Babbitt rod brass would also need to be converted to oil lub. Most steam locomotives around the world used Babbitt rod brass running on oil which operate much cooler than bronze and grease. Pouring Babbitt rod brass bores can also be centrifugal cast.
Dennis Daugherty

.

Its not my engine, but for strictly cosmetic purpose I wouldn't bother with doing any more than cleaning up the brass and pins, lubing them and putting them back together. As Kelly said, .125 is no big deal on a display engine. Magnolia did all of our brass work and we were very well pleased with them. I think the expense could be put to a better use.

After seeing plain bearings stolen out of cars and oak blocks used as replacements, just about anything will work in a pinch as long as it is wear resistant and lubricated well. Kelly, I’m wondering if Nylatron would work here in this application. I’m pretty sure it would be fine for the type of moves the OP is talking about, heck it might even work for slow speed operations. Would I use it on 844 at 60mph? Probably not, but in a museum setting it just might do the trick...comments?

If you're looking to get ahead on the mechanical restoration of this locomotive, this is a good project. If you're just trying to ensure you can safely move it around the yard, I'd think 1/8" wear in the rod bushings is fine and you don't need to replace anything. I'm sure plenty of branch line engines operated with at least that much clearance in the latter days of steam.

I personally witnessed NKP 765 operating with at least 1/8" clearance in the right hand main rod big end bushing in the early 80's. It made a hell of a racket, but it ran excursions at least 2 weekends in a row that way at up to track speed (65 MPH at the time).

.125 is NOTHING for yard movements, or even significant working. Ignore it and get the real jobs done. Use a heavy and water resistant grease to prevent moisture from damaging the bearings no matter the clearance. Concern yourselves more with assuring the valves and pistons are adequately lubricated in their bores, and the journals as well.

Thanks to everyone who has weighed in on this topic. We have the information we need and will proceed.

If this locomotive was on its wheels and the rods in place we would not be asking this question. However, the 2156 has been off its wheels for nearly 15 years. The guys who disassembled the 2156 had their hearts in the right place but did not know what they were doing. And they did not leave any useful documentation behind regarding the dimensions of the locomotive as it was when they started.

As much as we would like to, we don't have the budget to restore the loco to its as-built dimensions. So now we have to figure out what the wheel center spacing was. We must re-tram the locomotive to determine the shim thicknesses for the driving boxes that will put the wheels in the right position. And part of that is determination of the centers of the rod bushings. With the rod-to-rod knuckles severely worn and pitted and the bushings shot it is impossible to determine the spacing required because the spacing between the no. 2 and no. 3 axles can't be accurately measured. So we need to repair the worn knuckle pins and the bushings. Hence the question regarding the proper bronze.

Tram to the frames, not to the rods.

If the rods are egg shaped, have you considered the locomotive was out of tram and/or quarter to start with, and have any assurances the rods were bored to the correct length?

The locomotive was put into the park in the condition it was in when the NP retired it in 1956. Still had coal in the tender. It was worn out then and its components are still worn out. We will tram to the frame using the spec dimensions for the wheel centers to give us the shim dimensions we need for the driving boxes. But we will also get the "as retired" driver spacing from the rods. That will them let us make the decision on how best to proceed. But we do have to make the minimal repair to the knuckles and their brasses.

Should be no problem getting spacing from the old rods using a CMM machine. Half hour and you have your answer. I'm not sure I would have recast shoes and wedges for a cosmetic display, but you're not in any trouble, just extra work.