Alco C-855 R-T-R Build – Part 3 – Chassis Prep

This week’s post will be a continuation of my step by step build of an N Scale A-B-A Ready-To-Run set of Alco C-855 locomotives. And this post will be concentrating on the chassis and preparation required to get them ready to be assembled. You can find part one of the build here.

The chassis for the C-855 and C-855B is a Con Cor U50/Turbine chassis and I have three ready for the job.

The first check I always make is to see how they run. These are all in their original state and setup for DC operation. Each ran well in both directions, although they make the higher than normal amount of noise these chassis tend to make. The good news is later on I will be swapping the motors to solve this.

The chassis have lots of parts and striping down each chassis completely will be required as the base metal sections are going to be cut. Removing all the parts will prevent any metal filings getting into the gears and stop any heat which may be generated warping the plastic. If you’re going to be doing this with more than one chassis at a time I would recommend keeping all the parts for each chassis in separate bags or boxes. I use old foil trays left over from baking vegetables, washed up of course.

I would also recommend numbering each chassis. All the parts should be the same in each chassis but over the years Con Cor did make a few changes. Plus the amount of miles each model has done can also affect how the parts fit and run together. A worn part and a new part may not run well together.

The main sections are the top and bottom metal parts and as you can see below with 3D printed extension parts. Note each extension part has an arrow pointing to the front of the locomotive, and the orientation does make a difference.

You should always start with the top section as this will correctly set out the spacing of the two ends once cut.

I have marked the area to be cut out with a Sharpie pen.

The important surface is the step in the frame marked by the red line. The 3D printed extension needs to butt up to this in order to make the chassis the correct length. The area to be removed needs to be 2mm (1/16″) or less from this step. If it is longer the remaining metal will push the extender away and over lengthen the chassis.

As well as the center section there also needs to be some cutting done at the nose. Note: the A units need to be cut differently to the B.

Because both the Con Cor U50 and the Turbine have wide areas under the cabs which extend right to the front of the locomotives the chassis is wider here. But the C-855 does not so the ‘wings’ at either side need to be cut off. Also two notches need to be cut out as show by the marked area below. The nose needs to be 8mm (5/16″) wide, or less, and cut back by 7mm (1/4″). I tend to use the hole in the front left side as a guide, this makes the notches a bit bigger but that’s fine. (Too small and the shell won’t fit).

To cut the chassis I use a bandsaw but this can be done with a cutting disc in a Dremel style tool.

As you can see the 3D printed extension is much larger than the cut out part.

The nose section, for the A units, looks like this.

For the B unit the ‘wings’ need to be cut off only, not notching. You will see this later.

Test fitting the extension you can see the two areas which butt up and there is a small gap where the cut was made which is exactly what is needed.

The three sections can now be fixed together. I use an industrial superglue and a spray actuator as it’s fast and strong but you can use any good strong adhesive as long as it’s not designed to be flexible.

Because there is a gap between the cut face and the metal extender this allows it to be filled with glue.

And that’s it for the top section.

You can see in the picture below chassis number 2 has been cut for the B unit as it doesn’t have the narrow nose.

The second part is the lower section of the chassis. The 3D printed section holds the motor in place and because of the geometry of the part it makes it hard to get it in the right place. But because the top section is already set at the right length we can use this as a guide.

When I marked up the chassis for the photos, as shown below, I actually made a mistake and marked the section too far.

The red lines, shown below, are where the cuts should be made. Basically in line with the lower section. So no dimensions, just follow the existing line.

Once cut the two remaining bottom sections can be bolted to the upper using the original bolts. Don’t worry about fitting the plastic spaces as they will be coming apart again. I would also recommend installing at least two bolts in each end to avoid any rotation.

The lower section will be a tight fit and will take a bit of forcing in but once in the friction grip of the original parts to the new section will hold it in place. I then use a pair of pliers to align the bottom of all parts. Once I’m happy with the position I also fixed it with superglue.

With the glue all set the two newly extended chassis halves can be separated.

The lower section of the B unit also needs an additional few cuts. Most of the way around the lower section is a shelf which the shell sits on. But at the front the shelf is not there as this is where the loco cab is. As the B unit has no cab this shelf will need to be cut out. I place the B unit top section in place and draw round it as shown below.

And just to make sure I fill in the bit which needs to be removed.

Because this is a step and not a through cut I can’t use the band saw for this so it’s back to the cutting disc in a Dremel style tool. The first cut is made vertically down to the level of the step.