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Terrier Chassis - If at first you don't succeed ...

Ian Morgan



Well, I didn't give up. At the end of the last post, I had the chassis running nicely with the controller wired directly to the motor, but picking up from the rails was less impressive, despite the fitting of the 'Simpson spring pickups' rubbing on all the axles. The chassis was disassembled and re-assembled a few times, to no avail, and another crank pin came loose from a wheel and had to be re-soldered back in. Quartering the wheels was trickier as the motor was now solidly in place, but plenty of trial and error had the chassis running smoothly again each time.


At the same time, I was working on fitting the Dapol footplate to the chassis. As my version of the Terrier has sandboxes above the footplate, the sandboxes below the footplate were sawn, cut and filed away. If the under footplate sandboxes are to be retained, a little must be removed from behind them as the replacement chassis is slightly wider than the Dapol one. The photo shows the Dapol footplate with motor, the footplate with the motor and cage removed, and finally the footplate with some bits cut away to make room for the new motor to pass through it.




I also had to file a little plastic behind one of the front splashers to clear a gear, and a little from the front edge of the cab floor to clear the rear wheel flanges. Other than that, it fits the chassis, but the wheels will not go round because of the steps. I did not want to lose these nicely moulded features, and it seemed like there should be just enough clearance, but it did mean removing the bosses from the ends of the con rods and cutting the crank pins down to the very minimum. The centre cranks are fine, but the wire insulation was not enough to keep the con-rods in position on the short crank pins, so I had to solder washers onto the centre crank pins to keep the rods firmly in place. The loco body fits without any alteration, which was a bonus. There is even room in the tanks on each side of the motor to add some extra weight.


As I was getting no improvement in pick-up with each rebuild, I decided to resort to adding phosphor-bronze wipers bearing on the tops of the wheel treads. I used the remains of the Dapol pickups to produce these, and soldered them directly to the chassis. Again, there was no improvement. It seemed that the wheels just did not want to make good contact with the rails, and the pickups were removed again as they got in the way of fiting the footplate.


So, as a last resort, I followed Jerry Clifford's advice and made up a pair of rail skids. I had a sheet of .4mm phosphor-bronze which I cut and filed to shape, forming two long arms, with a kink near one end, bent to form the skids. I added another 180 degree bend at the other end in order to produce the most flexible springing possible. The ends were soldered to the bottom chassis stretcher plates.





Success. I finally had a chassis that ran slowly and smoothly on my short test track without stalling. I was so pleased, I threw caution to the wind and fitted the DCC decoder. This is a CT DCX75 which stands upright in the cab. It is hard to see it edge on, and will be completely masked when I eventually fit the crew.





The results I have captured on video. Hopefully the photos will explain everything. I will probably replace one of the skids, as the part that touches the rail is a little too short and seems to catch on some rail joints and on points.



Still to do, add couplings, touch up the chassis paintwork, think about adding the brakes, add the crew, then get on with my other two Terriers.

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Congratulations!! It's a great feeling when you finally get a loco to run smoothly and slowly.  So far (on my grand total of 2 locos) I've not had to resort to trying skids, I always thought they would be quite noticeable but I think once the brake gear is on (and they're blackened) they will be all but invisible.


I assume (since it's on Freshwater) that the video shows the loco as fitted with DCC, is there a visible improvement from when it was a DC chassis?  Being an old duffer I'm still a DC kind of guy :-)



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Ian, thanks.


I have been trying to build a working 2mm chassis for 25 years, and finally had success with this one. Lessons learned should make the second Terrier chassis quicker to build. I will also return to my 08 kit and get some turned muffs for it, to try to fix the badly meshing gears that brought work to a halt on it some years ago.


In the video, it is indeed running with DCC. However, it was running very well on analogue, which is what triggered the fitting of the DCC chip. From what I have read, there is little point in converting a loco to DCC if it does not run well on analogue. DCC can give smoother control for a good loco, with synthetic momentum added, but it cannot usually fix a bad loco.


In the video, I am just switching the direction and letting the decoder do the deceleration and acceleration.



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Well done!


I ended up fitting skids to my first loco for similar reasons. That chassis was entirely rigid though. Unfortunately these plastic bodies have so little mass that pick up is a problem. You'd probably find if you added mass it would have worked better, but that getting that mass into the body/chassis would have been very difficult. Everyone I've spoken to who's tried a GWR 0-4-2T has had the same problem. As you say the next one will go smoother.





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