GCR Class 5A – running chassis

I managed to sort the crank pins and get clearance. I removed the short 10 ba screw from the rear of the Mundy crank pins on the front axle and then cut the pin back to the boss.I then filed the boss back to approx half thickness and fitted a long 10ba screw through to become the crankpin. A tapped Slaters crank pin now acts as the retainer allowing clearance for the cross heads. I ended up doing a similar but not quite the same exercise on the middle axles in order to get it to run smoothly.
It’s running in on the rolling road as I type.


GCR Class 5A Chassis assembled.

What a difference a day makes (or was it the night off and a bottle of cider?)
Yesterday afternoon I scoured the etches to gather up the 18 parts required to make the two crossheads. As always one of them was quite elusive and took a couple of searches before I found it.

After a little bit of testing to ensure I had them in the correct orientation they were soldered up. They are a very clever design and they were both done in just over an hour without any of the stress of fitting the splasher tops to the J6.

GP Models GCR CLass 5A Crossheads

Following on from this I added the piston rods using some brass tapered clock pins that I bought a while ago. I then assembled the crossheads onto the slide bars and attached them to the motion brackets.
This was followed by the cylinder wrappers and then after cutting short the crank pins I assembled the chassis with the coupling and connecting rods with a view to giving it a test run.

Sadly, this is as far as I got because the Derek Mundy crankpins are so big on the front axle that they won’t clear the crossheads. Although the screw in caps are a reasonable thickness, I don’t think there will be enough meat in them to create the clearance just by filing them down.

At the minute I am pondering what options I have that don’t involve taking the crankpin back out of the wheels. My concern with removing them is getting them back in square without wrecking the wheels.

GCR Class 5A assembled chassis
GCR Class 5A assembled chassis
GCR Class 5A assembled chassis

GCR Class 5A The Chassis continued.

Next up was looking on the etches for all the bits for the cylinders and it was at this point that I discovered a couple more frame spacers that aren’t mentioned in the instructions. Thankfully they are quite easy to spring into place having trimmed the tabs shorter. As I was doing the first one I recalled having to do the same exercise when I built mine (and that was despite having Mike Cole’s build notes which seem to have been lost In the house move). What was more puzzling was where each one was supposed to fit within the frames.
Thankfully all I had to do was look under mine to refresh my memory.
I have highlighted the two in question in the photo below.

GCR Class 5A Chassis – additional spacer behind cylinders.

The one at the rear is mentioned in the instructions and it needs the hole for the brake cylinder to be to the left as you look towards the front of the loco.

In the apologies section in the instructions Garth apologises for there being no brake cylinder included. Having knocked one up from tube/rod etc. it seems that the reason for omitting it is that it interferes with fitting one of the plunger pick ups (and oddly the spacer had the hole for locating the cylinder in a vertical spacer which necessitated fitting a locating spigot in the side of the cylinder. I would have thought it much simpler to have made the frame space deeper with a fold line that would allow the cylinder to be fixed from the top. I am sure there was a reason why it was designed like that but we will never know what it was.

GCR Class 5A Chassis Sand boxes and rear spacer

I consulted with Brian as to whether to add a wiper pickup instead of a plunger for this wheel and his view was that having gone to the effort of making the cylinder it would be a shame not to use it so a wiper it is.

Having sorted the frame spacers and the brake cylinder I moved onto the sandboxes and the cylinders themselves making reasonable progress. All in all a good weekend’s effort.

GCR Class 5A Chassis
GCR Class 5A Chassis – front spacer
GCR Class 5A Chassis Sandbaoxes and Brake Cylinder
GCR Class 5A Chassis – Sandboxes

GCR Class 5A Crank Pins and Coupling Rods

Another good session at the bench on Saturday saw the wheels blackened and the Derek Mundy crankpins installed. I have to confess that I am not keen on them. I am not that comfortable with drilling such big holes in the Slaters wheels with the resulting chances of something going wrong.
I enlarged the holes with the pillar drill and I also used the pillar drill to push home the crank pins to keep them vertical and despite that one of them wasn’t in square and needed a little tweak.

Derek Mundy Crank Pins

Next up was the coupling and connecting rods, there is a diagram in the instructions on how to cut the coupling rod layers to allow them to articulate on the crankpin. Not knowing any better or having enough confidence to do it any differently that’s how I did mine. Sometime later, Steph Dale went to some trouble to post on Western Thunder a “how to” on cutting the rods to show me how to make them articulate as they should.
Having stored this up for a rainy day I adjusted the cuts and made use of a couple of the spare part rods supplied to make them articulate behind the middle crank pin as they do on the prototype.

There is an etched hole in the outer layer (presumably for a dummy pin) I used this to mark up where to drill the rear layer 6mm. Once all the layers were soldered together and cleaned up, I tapped the hole in the back layer 14ba. Then I threaded some .9mm nickel rod 14ba and made a nut from tube files to a hexagon. Once soldered to the threaded rod I was able to use a 16ba nut spinner to tighten it in to the rods making a nice neat articulated joint.

GCR Class 5A Coupling Rods

GCR Class 5A Basic Chassis

Last weekend I managed to get the basic chassis together with the compensation beams.

One thing to note if anyone comes to build one of these, is that all the spring layers go on the outside of the frames or they interfere with the compensation beams. Needless to say, I had forgotten this from when I did mine and the instructions are a bit vague in this area. Which meant that after making a really neat job of fitting them both sides, I ended up taking them off the back and adding them to the front.

The kit comes with one of the frame spacers in the form of a motor mount which I made use of in my original build but I left out because Brian (Wainwright) whom I am building it for, has supplied an ABC motor gearbox. It does mean that I will have to do something about the holes in the frames though.

GCR Class 5A Chassis
GCR Class 5A Chassis
GCR Class 5A Chassis

Great Central Railway Class 5A

In an attempt to get caught up with my backlog of builds I have taken a leaf out of another modeller’s book and have decided to try to build one loco during the week and a second over the weekend. The idea is once I am on top of my back log of commissions, I will build my own stuff on a weekend.

Having made the decision a couple of weeks or so ago, I made a start that weekend on a GP Models Robinson GCR Class 5A. I previously built one of these for myself but finished mine as an LNER J63. Which the Class 5A became, when inherited by the LNER in 1923. This one is to be finished as a GCR example.

Upon opening the box I found that the gent that I am building it for had already supplied a few extras but after examination of the castings bag, it revealed that some of them were quite poor. I Although I replaced a few of the more vulnerable castings like Oilers etc. I don’t recall the castings in my kit as being too bad so I was a little surprised. An exchange of emails later had me placing an order with Laurie Griffin for a few items. The one casting that was in my view poor but not available anywhere as a replacement (that I know of) was the backhead. This is a resin casting and perhaps the moulds were worn from when I got my kit, as mine was perfectly usable.

When I saw the casting I recalled that lurking in a spares box was a piece of brass that I had cut to shape for a round top backhead prior to getting more information and making a second more accurate backhead for a 4mm scale loco around 12 or so years ago. I dug it out and to my delight it only needed a minor amount of filing and a few mm cut off the bottom, to be the right size/shape to replace the resin casting. What it did lack was depth, but that was overcome by soldering a curved strip of etch offcut to the back of it.

This is the original casting which aside from anything else is slightly lopsided.

GCR Class 5A Backhead

This is what I came up with as a replacement which should pass muster in an enclosed cab.

GCR Class 5A Backhead
GCR Class 5A Backhead

Finally a side by side shot for comparison.

GCR Class 5A Backhead