very rare brass Key 4-10-2 Southern Pacific

[mmagliaro]

Max, my apologies.  I didn't want to disassemble it one more time to make measurements, so I made them with the shell on and thus have a bit of estimation.

But with my caliper, here is what I came up with.  All are rough measurements.

Driver dia = 9.41 mm
driver + flange = 10.58 mm
flange measure by itself, depth = .62 mm
axle dis between 2 axles = 10.89 mm
axle dis from first to last driver = 44.48 mm

Hope that is somewhat useful.

So between any two drivers, we have a gap between the flanges of only 10.89 - 10.58 = .31 mm, or .012"
That's mighty tight.  But like you said, I think these are estimates.  If you divide 44.48 by the 4 gap inter-axle
spacings on the 5 drivers, that's 11.12 mm, not 10.89, and the 11.12 is probably more accurate since it's a large
measure over more distance.  That implies .54mm gap between drivers, or about .021".  That's more reasonable,
allowing for the "wiggle" inherent in mechanisms like this, and room for some brake shoes.

Still, .021" is nice.  That's part of how the drivers end up looking so good together. 

Thank you for the measurements.

[randgust]

As a Santa Fe guy, I have to admit that's still once of the nicest N brass models I've ever seen.   Really impressive and thanks for posting the photos.  But, as  Santa Fe guy, that's worshiping the enemy.....

One thing you never seem to know about brass is how many were ever made.

[spookshow]

I'd be very surprised if there were more than 100 of these things out there (50 "early" and 50 "late"). Total WAG on my part, but based on the infrequency with which the show up on eBay, I'd bet that's not too far off.

-Mark

[Loren Perry]

Yes, many brass steam locos have sprung driver axles, but in my experience those springs are way too stiff to actually result in a workable suspension. Springs are slightly large diameter than the MTL coupler springs, but they are wound out of much thicker steel wire (much, much stiffer than the coupler springs).

I ran into this same problem (stiff springs) back in the 1990's when I purchased a pair of then-new brass USRA 2-10-2 engines. The drivers were all sprung but were so stiff the "working" suspension was useless. So I decided to make my own softer springs by winding some .006" brass wire from Detail Associates around a tiny drill bit so as to match the dimensions of the stock spring. I then tweaked it until the coil spacing and overall length were correct. Finally, a No. 11 blade was used to cut the finished spring to length. Repeat nine times to equip one locomotive.

The result was very successful. The locomotive was then able to operate smoothly over rough track with all axles being in contact with the rails at all times. No operational problems were encountered and the engines ran flawlessly for many years until I eventually sold them.

[peteski]

Peteski- Yes I know that a lot of brass steamers have strung drivers, but I had not see any N scale steamers that had them.
I have two HO brass steamers apart (painting projects) right now. Each one has springs on the drivers. Like you, I think the springs are way too stiff. It takes a lot of pressure pressing down on the locomotive to make the springs compress. They might just as well mounted the drivers solid.  IMO. I might try some NWSL springs to correct.

I don't have too much experience with N scale brass steam locos, but all I have ever worked with did have sprung drivers.  I think the manufacturers do this just because they can (and of course because the 1:1 drivers were all sprung too).  But what's puzzling is why those springs are so stiff.  Since those springs are likely specifically manufactured for each model, they could have used thinner wire to make them softer, to actually have a working suspension.

Maybe the reason those springs are so stiff (to make the wheelbase pretty much rigid in normal operation) is because the designers were afraid that if the suspension actually flexed over rough track, that would make the siderods bind?  But the stiff springs are still there, so the owner of that pricey model can brag to their friends that the loco has a working suspension. 

[woodone]

The only brass loco I had was an Key Challenger steamer.
I had it apart enough to fix the front drive, but never dropped the drivers out, so I don’t know if they were strong or not.
With such small movement up & down and all the slop in the side rods, I don’t think there would be any binding.

[peteski]

The only brass loco I had was an Key Challenger steamer.
I had it apart enough to fix the front drive, but never dropped the drivers out, so I don’t know if they were strong or not.
With such small movement up & down and all the slop in the side rods, I don’t think there would be any binding.

I suspect that your browser keeps auto-correcting "sprung" to "strong" and "strung". 

As far as being able to tell if the drivers are spring or not, even though the range of motion is very small, one can easily tell whether the drivers are spring or not just by pressing on the drivers.  The movement and springiness is be quite apparent.

[Mike Madonna]

I'd be very surprised if there were more than 100 of these things out there (50 "early" and 50 "late"). Total WAG on my part, but based on the infrequency with which the show up on eBay, I'd bet that's not too far off.

-Mark

Mark,
I would agree with that statement. The 3 cylinder was one of the last N scale SP Steam offerings from Key. When they re-ran the MTs (1999-2000), there were 5 versions (the original 1984 run had 4 versions; Shasta, Sacramento, 49er & Valley Daylight). The later run featured the previous four versions and a fifth (and rare) 4-8-2, the MT-5 #4370 "1950s" version. I'll bet there were not more than 100-125 of each....

[JMaurer1]

MRFs did the same thing in HO brass. Back when I was lost in HO, most of my engines were brass (I hated detailing Athearn 'blue box' engines, especially adding grab irons, to make them look 'right'). Drivers were usually sprung, but the springs were so stiff, even using a finger to push up on the driver would only make it move a tiny bit. After checking, my few pieces of N scale brass DOES have springs as well, but short of this thread, I would have never noticed. You would think that if they used much softer springs, the springs might actually allow the engines to run better as they drivers would maintain better contact with the rail (and have better electrical pickup as well).

One of the main reasons I left HO for N was I wouldn't need to drill and add the grab irons in N scale...of course, now people are doing that as well and I hate every one of you who does this (j/k).