MDC 3tr Shay

Disaster and recovery

January 02, 2006

I temporarily suspended my work on the Shay because I'm also working on a Dutch engine (see NS 7000) and I spent a few days tuning and tweaking the gearing and valve gear of this beautiful, but maybe to American standards odd looking, model.

I had closed 2005 with several running trials and high spirited I took up work on the Shay again in 2006. When I did, it occurred to me that the axle of the top gear was looking rather strange. I disassembled the gearbox to check it out and in the process the axle broke off!!

The broken axle with the universal cup still attached. Note the worn out area of the axle hole in the gearbox halve

On the back side the this hole was still intact, so I could stil use this gearbox halve

The most probable cause was my last running trial. On reassembling the motor and gearbox for the last time I forgot to insert the shim that keeps motor axle in line with the universal. There must have been some pressure on the gear axle causing the plastic to melt. The gearbox halve on the motor side proved to be damaged as well but this wasn't much of a problem. The broken gear however was. Since getting spare parts would take a long time and would be a little complicated I decided to take a long shot and try to fix it.

I bought 2,4 mm round brass. I flattened the broken side of the axle, determined the middle and drilled a hole through the gear. I had to ream it a little but after some trying the gear slid on the brass. Some cutting and filing brought back the axle to size. Sounds easy but it took me an entire day!!

Drilling the hole in the gear was a nerve wrecking accurate job

But it is possible!!

Of course after this the gears wouldn't run evenly anymore. No one can do such a job within the tolerances desired without extensive tooling. So I started tuning the gears again. But soon I realized that the gears slipped, having too much space in between. I turned to my 2-truck Shay kit. And now a little miracle happened. The repaired gears of the 3-truck fit almost perfectly in the gearbox of the 2-truck Shay, a little snug rather than loosely, and vice versa!! So after only one hour of carefully deburring and sanding I had once more a fully operational gearbox that worked even better than before the disaster. The gearbox that remains for my 2-truck Shay needs some attention but I'm confident that I can get it working. Jeff Johnston mentions the miracle of the size differences of the various copies of the Shay. Although the parts come from the same molds they may fit very differently. Well, in my case this was to my advantage: the gearbox in the 2-truck proved to be a little smaller.