A while back I constructed an early IP Engineering 'Jessie' diesel loco kit (see How I constructed an IP Engineering diesel) but very quickly found that the nylon gears in its gearbox were insufficient for the loads my railway places on it.
A replacement IP Engineering gearbox very quickly wore out and so a kindly fellow modeller constructed a bespoke gearbox for me based around some brass 00 loco gears.
This lasted me a season, and so when I dusted off the loco to resume service this year, I found this gearbox too had succumbed to the dreaded wear. Having had a great deal of success with commercial loco blocks on my other track- and battery-powered models, I cast about for a suitable block to instal underneath Jessie (or Wynford as she is known on my railway). The most appropriate I could find was a USA Trains short wheelbase motor bogie, but after making several enquiries I discovered this is now no longer available. Whereas the wheelbase of Jessie was 60mm, the nearest I could find to this with extended axles for the fly-cranks was the USAt medium power bogie with a wheelbase of 84mm. On downloading the datasheet for this motor block from the g-bits website, I discovered it would fit beneath the chassis, though of course I would have to extend its wheelbase (and also source some longer coupling rods).
First of all, I had to adapt the motor bogie for battery power, by removing the track pick-ups. The base of the block was removed .....
.. and the skates unclipped.
Two screws holding the plates covering the wipers for the axles were then removed.....
...... and the wiring snipped from the motor contacts.
The block was reassembled. The coupling rods were removed from the loco, by prising open the spring-clips.....
...... and then the grub-screws holding the fly-cranks were unscrewed.
The sides of the chassis could then be unscrewed........
....... and the old motor and mechanism extracted.
The motor-block was then test-fitted and the position of the new axle holes marked for drilling. The rear axle holes were retained as these provided clearance fro the switches and charging socket. I also decided to remove the bushes from the axle holes as these were redundant and also reduced the working length of exposed extended axle for the fly-cranks.
To hold the block in place, a U-shaped bracket was fashioned from brass strip and fixed to the chassis. The ends of the bracket passed through the slots for the skates on either side of the block and were bent over to hold the block in place. The fly-cranks were then screwed on to the extended axles .......
....... and the loco was test-run.
I was unable to track down a source of coupling rods with 84mm centres and so these were marked out on a piece of 64thou brass strip and filed to shape in a vice.
The cranks required a little adjustment to ensure they were properly quartered and some more test-running was undertaken with a full load of tipplers up the steepest gradients and around the sharpest curves.
She tackled the gradients without hesitation but there is a noticeable slowing when she negotiates the R1 curves which still exist on my railway. This is presumably a side effect of the longer wheelbase. I am intending to remove all the R1 curves over time and so this is something I can learn to live with.
The redundant holes in the sides of the chassis were filled with epoxy filler, then filed and sanded smooth ........
...... before the chassis was given a coat of matt black acrylic (ordinary black mixed with talcum powder).
The chassis was then weathered with a mix of brown and black weathering powders and given a light coating of matt varnish to seal them.
The loco was then tested once more.