Eccentric Crank

Model Railroader General Discussion (Model Railroader)
1

Hi, I have a problem with my 4-4-2 atlantic steam loco. The eccentric crank isn’t spinning like its supposed to. Insead, it stays on one angle and moves along with the connecting rod. Did anyone else have this problem, and how can I fix this?

2

Not sure if I understand your problem. The eccentric crank is supposed to be fixed firmly to the driver and rotate with the driver. The usual problem is the crank coming loose and slipping. The usual fix is either tighten the mounting bolt or use Loctite.

3

I don’t really know how to explain… it can’t be fixed firmly to the driver…if I tighten the screw, it will be pushed on to the connecting rod, therefore move along with the connecting rod and not rotate. And there is nothing to separate the eccentric crank from the connecting rod.

4

I’m guessing now, but I think your model is one by MDC/Roundhouse, no? By “connecting rod” you mean the main rod, right? OK, then, first of all make sure that the motor is not mounted. All mechanism work should be done without the motor mounted, so you can get everything lined up and operating smoothly.

  1. Remove all rods from the drivers and inspect them carefully, removing all flash from the rods and their crankpin holes and especially the flat areas where they mount to the drivers, and rub against the main rod and eccentric crank. Make sure the drivers are correctly placed in the frame, with the insulated drivers on the fireman’s (left as viewed from above with the pilot pointing away from you) side. Oil the axles lightly with a good plastic-compatible oil. Fasten the cover plate down and make sure the drivers rotate freely in their slots. The pair of drivers with the long crankpins is the rear driver set.

  2. Mount the side rods, making sure they also rotate freely on the driver crankpins. Add the screws for the front pair of drivers, firmly, but don’t crank down too tightly on the screws, or you could strip out the holes. Do this on both sides of the engine.

  3. If you have not at this point riveted the valve gear and mounted the crossheads and valve gear to the chassis, do it now. Make sure the main rod is properly fastened to the crosshead.

Note: at this point work on one side at a time!

  1. Rivet the eccentric rod and expansion link to the eccentric crank. Mount the expansion link to the valve gear frame as per the instructions.

  2. Slip the main rod over the crankpin on the rear driver set.

  3. Rotate the driver set so that the crankpin is down (closest to the rail), and the counterweight is at the top.

  4. Set the eccentric crank on top of the crankpin, and screw it down so that the end of the crank is pointed appro

5

whew! thank you for a good question…for just a brief moment i thought you had been talking to my wife, listening to her description of my attitude last week. Eccentric-check; bit of a crank, double check. Smile, don H.

6

Yes, I’m an eccentric crank.