Large Scale Central

Connie wheelbase modification

Modeling Motive Power
#1

I have a Bachmann 1:20.3 Connie that has a split gear which I will be replacing.

On my layout I run mostly 1:22.5 scale locos so the layout has a couple of tightish curves and LGB R1 curve turnouts that are fine for them (it was built with that scale in mind) but the Connie just struggles with and cannot get through the turnouts.

Now redesign of the track is not an option because I have claimed all the real estate I can get away with.

While looking at the chassis I had a brainwave and thought I could replace the no flanged wheels on the drive gear axle with the flanged ones from the sound cam axle ie have a flanged/non flanged/flanged/non flanged configuration instead of the current flanged/2 non flanged/flanged one.

My thinking is that the wheelbase will shorter, about a similar length to my side rod diesel (my next longest wheelbase loco), that has no trouble with the curves thus improving its running but not changing its looks that much.

Could I ask anyone who has a Connie to look at theirs and make a comment if they think this is a good idea or am I just dreaming.

Anybody else’s opinion will be welcome as well.

#2

You will indeed reduce the wheelbase, but you may have issues of the rear driver (on one side) dropping “inside” the rail on a curve, and what happens when the track straightens out.

When you have center blind drivers, they are “suspended” between the front and rear drivers, so that is “level” between them, i.e. less likely one of the center blind drivers will “drop down”

When you move the blind driver to one end, then if the loco “rears back” a bit then I believe the problems with the blind drivers increases.

You could try it, but you probably need the track to be very flat and the loco needs to stay “level”, soft springing might mess you up, for example.

Greg

#3

Thanks for the advice Greg I didn’t think of that.

My next bright idea is how about I modify it to a 2-8-2 with a pony truck under the firebox to support the blind driver around corners.

#4

On the 10 wheeler 4-6-0 the center driver is blind and it is also a smaller diameter than the flanged drivers. Check yours, they may be smaller too, hopefully enough to prevent the drop. One could also remove the spring and block the driver up…

John

#5

On making a trailing truck that actually supports the loco… .this does not happen often in our world, it seems to be difficult for some reason.

Greg

#6

I’m not at home to see test the geometry of a 2’ radius curve relative to the drivers on the Connie. My gut tells me you should be fine, as the offset shifts from both blind drivers being offset to the inside of the curve to one being inside and one being outside. The wheelbase is compact enough to where I don’t think you’ll drop the wheels off the railhead. If I recall, Dave Goodson (TOC) said the loco would go around a 2.5’ radius curve with only a modification to the deck plate between loco and tender. A 2’ radius shouldn’t be too much more of a stretch with the altered wheel geometry. I can check when I get home.

Having said that, I think the suspension or wheel overhang would be the least of your troubles. That’s an awfully large loco to try to get around a 2’ radius curve. The overhang to the back of the cab will be dramatic. If you move the flanged driver from the #4 to #3 axle, you’re going to increase this overhang. (I might consider swapping the #1 and #2 drivers instead for that reason.) Also, the tender drawbar attaches to the loco towards the back of the frame. The further the frame moves out from the center of the track, the more askew the drawbar will get relative to the tender, whose pivot pin will be pretty near the center of the track given its proximity to the pivot point of the front truck. That’s going to do two things. First, it’s going to put lateral pressure on the tender as it goes around the curve, especially as it tries to drag a train through the curve as well. That could lead to derailments. You’re going to need a long drawbar to keep the tender from hitting the locomotive as it goes around the curves; probably longer than the stock one. I’d consider mounting it much further forward on the locomotive so its pivot point is closer to the center of the rails. You’ll also need to replace the rear truck with one that has a truck-mounted coupler.

In terms of adding a trailing truck to it, check out David Fletcher’s conversions of the Connie to a K-27. They look great, but you’re making an even longer loco, then, which will only exacerbate the issues relative to getting it around a 2’ radius curve.

To be frank, I can’t think of a reason why this wouldn’t work, but I don’t know that it’s something I’d put a whole lot of energy pursuing. The wheels are easy enough to swap out since they just press onto the axles. Try it, see what happens. The worst is that it doesn’t work, which puts you back where you are now.

Later,

K

#7

I think you will find you will not be able to move the wheels on the third axle. I believe the crank pins are longer to allow the piston rods to fit on as well as the drive rods.

#8

Tony, the crank pins are on the counterweights. I think the wheels themselves are the same, just flanged/unflanged being the only difference.

Later,

K

#9

Kevin, You are correct. That will teach me to engage brain before opening mouth.(http://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)

However, swapping the wheels will require removing the axles from the chassis, will it not?

#10

Yes, but since the drive gear is being changed at the same time, you’ve done most of the disassembly already. It’s just a matter of removing the #4 axle as well as the #3 axle and swapping the wheels when you reassemble everything.

Later,

K

#11

I’m with Kevin. It seems like an awful lot of effort to possibly make a loco that is really too big for your RR get around your curves. You might be better off finding someone to swap for a smaller loco more suited to your RR.