OK I’ve got a curiosity question.
Let’s say I have a Rivarossi Cab forward, or a big boy, and I want to change the drivers, how hard is it? Now part two of the question, does it become harder if I want to use larger diameter drivers?
Remember I’m a freelancer so I’m not concerned with the why or the who on this one.
Simply put if I wanted to have a big boy or cab forward with say 80 inch drivers from a GS4 or FEF, could I do it.
Thanks ahead of time.
Simple answer - it won´t work!
Why would anyone want to change the diameter of a signature engine like UP´s Big Boy or Challengerm or SP´s Cab Forwards and GS-4s, escapes my understanding. These engines are clearly not suitable for freelancing, unless you intend to build a caricature of a railroad.
More than drivers would be changed if I were to do a freelance version of the Big Boy.
And also I know that those old rivarossis run pizza cutter flanges, another reason to replace the wheels.
i put new drivers on an old ahm unit i went with rp25 drivers the same diam. as the flanges of the pc ones but it also involves changing the linkage and rods.had no problems other than adapting a new can motor . as a after thought 80 inch drivers might have clearance problems , unless you made a new frame.
If you change the diameter of the drivers, you will have to make a complete new set of valve gear and connecting rods and might have to replace the cylinders. Even if you change or modify some details, that loco will still look like a Big Boy in too small shoes.
Turning down the flanges to a near RP25 profile is certainly the much easier job.
Given the small distances between drivers, it would be major chassis surgery to make this happen; let alone the need to fabricate new linkage and rods to accommodate the longer throw due to the increase in diameter size. You’d also need to requarter the drivers. You should wait till you finish medical school before tackling something of this scope.
Have you changed eras again? I thought you were modeling the 70s-90s now.
Driver diameter is an intrinsic and carefully engineered criteria for the locomotive designers. There’s a delicate balance between all of the factors that get that available boiler horsepower to the rail.
Very true, Tom. The first New York Central Niagara, No. 6000, was built with 75" drivers but designed to accept 79" which were subsequently fitted shortly after construction. In a similar vein, some of the Mohawks were built with 69" drivers but the driving box pedestals were spaced to accept 27" drivers if needed. The later group of L-4 Mohawks were built with 72" drivers and were intended for faster, dual service use.
Sometimes, but not always. The crank pin to center distance will usually stay the same. The Piston diameters can be varied slightly but the stroke will often stay the same.
Quartering should also stay the same, I believe.
Most frequently a smaller diameter driver is applied to locomotives as they get old and “slow down” as many of us old timers are prone to.
Look at NYC’s famous 999 that started life with 86" drivers, 19 x 24 inch cylinders. Toward the end of her career she was hauling milk trains in Pennsylvania with lowered boiler pressure and 70" drivers (same cylinder size).
The next time you have a few extra coins in your pocket take a look at one of the used book sellers, Amazon or Ebay for Kalmbach’s Model Railroad Steam Locomotive Cyclopedia Vol: 1.
I found a nice, used, hardbound copy for under
This is a silly idea.
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The great thing about freelancing is you can use an existing mechanism and change the boiler or shell to make it unique.
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There is no reason to do it the other way.
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I don’t think the others have even given a fraction of all the work involved. You will need to build a new frame. Others have done this kind of thing successfully, maybe you can too.
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But hey… you have a job now… go ahead and buy all the parts and try it out. I don’t think anyone telling you it is beyond your skill set will prove it to you any more than actually trying it out.
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-Kevin
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Rivarossis Cab Forwards are very good runners as is but . . . . any attempt to modify the wheels has been a failure. I gave a set of wheels to an excellent machinist with at least 30 years experience working for NASA machining small parts to remove the large flanges. The wheels looked perfect but they would not work in any Rivarossi frame with out massive derailing. As a result all 19 of my Rivarossi articulateds have large flanges.
I also would like to mention that Rivarossi steam locomotives do not use standard quartering so you must make a Rivarossi quartering gauge for 87.5°.
I have been successful in doing a lot of kitbashing to my Rivarossi articulateds over the last 20 or so years but I’ve never had any luck with any messing around with the wheels. The Rivarossi driver engineering is as perfect as one would want. The only problem with the Rivarossi engineering is by driving both sets of drivers with one driver assembly they have a tendency to wobble, the older and more run time the worse the wobble. My fix for the wobble is dual can motors, that virtually stops the wobble as well as more avail
I think it’s worth mentioning that RDG Casey, who does some of the finest steam locomotive scratchbuilding (prototype or otherwise) I’ve seen online, appears to begin with drivers that are the right size for the locomotive desired and fabricates or bashes everything else around that fixed point-- even the valve gear, if needed. That tells me something about the driver size and their location in the chassis being likely the least changeable component of the locomotive if one wants it to remain a running piece of equipment.
Phil
Make a mental image of the prototypical driving wheel set. Their axles have to be an absolute minimum distance apart to clear for brake hangers, shoes, tire flanges, and in some cases the sanding tubes. Now increase the diameter and what must you do? You must separate those pivot points, the axles, by that much more to accommodate the increased girth and diameter of the larger tires. Now that you have separated them, what have you done to the distance between the crank pins? After all, they, too, revolve about newly-separated axles.
Now you need a main rod that can reach further because the axle with the main crank has been moved backwards along the frame…umm…along with making new axle boxes in the frame because they have to move as much as the axles do. As long as the cranks don’t increase in length themselves, the stroke in the cylinder and on the crosshead will be the same.
If you need a longer main rod, won’t you also need new side-rod linkages because they have to link axles at a certain distance apart? Increase that distance and you will have to increase the pivot points along contiguous rods or along tandem rods.
If the main crank distance extends further from the crosshead, you’ll also have to provide a longer eccentric rod if you don’t move the expansion link and its mounting.
I won’t go on, but hopefully one realizes now that it ain’t so simple.
I get it, it’s no easy feat.
As long as you keep the original drivers with the original running gear in its original frame you can pretty well kitbash everything else on a steamer.
This morning about an hour after my post above I lost a driver on my last build Mel brass frame Cab Forward. The basic engine is roughly 42 years old and it was towing 10 heavyweight passenger cars up a 3½% grade 32’ radius helix. I checked the drawbar on the cars and that surprised me, 3.2 ounces in the helix. That’s well below what I expected.
Because I have a bunch of Rivarossi parts it was a quick and relatively easy fix, took about 30 minutes to remove the trailing pair of driver wheels and slip in a new one (well not new but both wheels were tight on the shaft).
It’s back in service towing my SP Lark passenger cars through my tunnels.
Even with all the hours on my old refurbished Rivarossi locomotives that is the first driver I’ve had to replace. Come to find out they have fluted axles. I’ll experiment using CA as a repair for the dinged one.
This was the
I’m not familiar with Rivarossi, but my one-time experience with swapping wheels would suggest to use new wheels from the same manufacturer.
A long time ago I used the chassis and motor of a Mantua “Little-Six”, an 0-6-0t with uneven axle spacing, as the platform for a scratchbuilt 4-6-0. I replaced the original 52" wheels with the Mantua next-size-up, 62" wheels, and turned the chassis front-to-back to get the correct ten wheeler spacing (axle 1 & 2 closer than 2 & 3).
Once I determined that there was enough clearance for the larger diameter tires, it was an easy, drop-in conversion because the axle diameters were the same (perfect fit in the frame’s bearing) and the original side rods fit perfectly (= to axle spacing).
Jim
As you’ve found out, that’s a terrible idea.
BUT.
What might be doable is to put different “drives” (drivers, rods, valve gear, frame and cylinders) under a boiler. In fact, I still recall Bill Schopp doing an article in RMC where he had a Tenshodo GN S-1 (4-8-4) and a United (?) Santa Fe 2-10-2. He switched the “tops”, and had a GN 2-10-2 and (I guess) a Santa Fe 4-8-4 (with 73" drivers). Or something like that. It’s been awhile since I marveled at the audacity of re-arranging brass engines.
So. Maybe you scrounge up a Rivarossi cab forward. Then you find two matching drives. Since you don’t need to replace 8-coupled drives with the same thing (what’s the point?), that would leave the possibility of having a 4-6-6-2 or 4-10-10-2 cab forward.
The trick with the above is that the length of each of the two new drives has to be about the same as the length of the original drives. The biggest determiner would be driver diameter. For the 4-6-6-2, I figure 80" drivers would work. For the 4-10-10-2, I figure 50". Thing is, no one would have built that latter. It’d be, essentially, a giant cab forward transfer switcher. Not a big need for that. But the 4-6-6-2 might just work out. SP actually had some small versions of tha
Yes of course, I was just wondering if it was possible, it’s not in my immediate project iteniary.
A 4-10-10-2 cab forward sounds cool, I’d make it like the 5000 class three cylinder.
Thanks for the replies.
As noted there are so many variables in trying to do this. Bearing and axle sizes differ for example, although I think most of the old Mantua die cast steamers at least has the same axles and bearings. Perhaps Penn Line/Bowser ditto. But they were not the same as Rivarossi or other makes.
Even if you swap one locomotive’s 80" (or whatever size) drivers for another locomotive’s 80" (or whatever size) drivers there is still the issue that the drive rods may not connect up at the same distance from the center of the axle in both cases, so you may need all new rods including main rod, the valve gear, and list of complications goes on. Plus not all locos with the same sized drivers had, as noted above, the same distance between axles in the frame.
And worm and gear matching is yet another issue.
But there are guys who have swapped driver sizes on commercial die cast steam locomotives and also with brass and done whatever other work is required to make it all work.
There have been alternative aftetr-market drivers purposely designed for particular model locomotives however. Years ago an outfit, cannot recall the name, had a set of spoked 80" drivers that was a drop in replacement for the BoxPok drivers the Mantua B&O Pacific came with, allowing you to either backdate the locomotive or model the engines that mixed spoked and BoxPok’ed drivers.
And didn’t NWSL offer a complete replacement set of drivers for the Rivarossi/AHM cab forward, with NMRA compliant flanges and if memory serves, were at or closer to the actual diameter of the SP drivers, seeing as how AHM/Rivarossi almost always had undersized drivers to accomodate the monstrous flanges? I think it was still up to the purchaser to put a gear on the axle and then successfully re-quarter the geared drivers. NWSL offered jigs and tools to do both tasks but still not something everyone feels comfortable doing, particularly gi
Really? With 50" drivers (readily available from Mantua/Tyco, I think), you’d have a giant hulk of a machine with a top speed of 30 mph*. If you’re lucky.
What exactly is so cool about such a loser locomotive?
Ed
*A steam switcher with 50" drivers MIGHT make it to 45 mph. On a good day. And not worrying about damaging the track. A 4-10-10-2 would have to have heavier main and side rods, because of the great increase of forces through the rods. And that would likely max out the room for counterweights. So you’re getting a poorly balanced steam loco. Which radically lowers the top speed.
You said it not me.
Just pick up one of these and watch the drivers roll.
Leave the engineering and design work up to the “experts”.
http://mrr.trains.com/news-reviews/staff-reviews/2008/02/mth-electric-trains-ho-erie-triplex
Cheers, Ed