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Making Your Mechanism Run Like a Swiss Watch (Bachmann)

From Joerg Seiler
Wed, 14 Aug 1996

As promised here is the long awaited “What I’ve done with my Forney” dissertation.

Brick’s lamenting that no one has filled the corridors of the HOn30 Mail Car with Forney talk prompted me to spend a few hours last week to start the project.


First I read the instructions thoroughly which is something I usually leave to last,….. makes projects more interesting!?!.

I have set myself up with a small loop of track on a 57″ x 35″ arborite covered desktop that I salvaged from a bunch of junk thrown out at work. On this I have an oval of Kato track. I bought this a while back when my father brought me an n-scale Atlas GP38 that he found at a flea market for $5. The motor was burned out. Not wanting to disappoint my father by telling him I was not an N-scaler I bought the track and got the little guy running. To cut an already long story short, I never thought I’d use it for anything more because I was into HOn30 at the time. Now I’ll use it for Brick’s rail truck!

I use this table top for run-in purposes and as a work table for tinkering with mechanisms, very handy as I can vacuum of the track and clean it thoroughly without having to worry about damaging scenery or missing trouble spots in tunnels. If there’s something wrong with a mechanism, it’s the mechanism not some track problem or dirty rails.

I started running-in the Bachmann 0-4-0 and like the Plymouth it ran a little rough at first. I noticed a slight wobble as well which didn’t please me. I removed the siderods and still noticed the slight wobble. I suggest removal of the siderods for run-in on this mechanism so all other small problems can be cleared up before messing with the valve gear.

I let it run at around 5-6 volts for a few hours and noticed there were no problems with excessive current draw. I use a laboratory power supply providing me with pure DC and a maximum current control. That’s really handy in the event there is a short, the current limiting saves the motors from damage. I strongly suggest a current meter of some sort to alert you to problems. Mine draws less than 100ma.

As the mechanism runs in it will loosen up and start to run faster. When this happens I reduce the voltage to keep the speed down and avert any destructive
heat damage. I always run any mechanisms as slow as they will go reliably when I run them in, and continually reduce the voltage as they become smoother
running. Usually this speed is around 40 scale mph to start and slows down to about 15-20 scale mph. That is without pulse. I do all of this over a several hours on a weekend or weekday evenings. I set the table and power supply up in the living room so I can keep an eye on the patient while it is running. This way I can work/read/relax/model at the same time. I will usually not take a mechanism apart until it has had a good 10-15hrs run-in time, unless there is something seriously wrong with it.

I added a little bit of grease to the worm and gear after the first few hours. I use Labelle #106 as it is the best grease I have found for plastics. I also noticed on the Bachmann mechanisms that the bearings in the motors become tight after prolonged running. I put a *tiny* drop of Remington Rem-Oil on each motor bearing. This seems to do the trick and has worked for both the Plymouth and the Forney Bachmann mechanisms. The speed has reduced dramatically now and the mechanism is running a lot smoother than at first . It does still have that wobble and if I reduce the voltage even further there is a distinct bind every revolution. Time to take the mechanism apart and find the real problem.

To take this one apart all the wheels have to be pulled off. Take out the little screw that holds the wheel pickups on, this also holds the metal plate to the body. I took all the gears and cleaned them completely. I took all the little bits out of the gear teeth by running the end of a toothpick through them. I found no problems with the nylon gears. I also cleaned all the wheels. These have the backsides greased at the factory so they run smoothly against the metal chassis plates. Again I found no problems with these wheels. You can chuck these in a dremel tool by their axle and rotate them slowly to check roundness. There should be no wobble and there wasn’t. So where is the problem? The problem lay with the little metal side plates. The holes had burrs on them and the plates themselves were not quite flat. These plates are punched from sheet metal and therefore have a sharp pronounced burr on one side. I deburred the holes with a large drill bit twirled with my fingers. Always use a drill at least twice the diameter of the hole you are deburring, otherwise the drill will catch and cause
more burrs. Then I lightly ran a file across both sides of the plates to make sure they were absolutely flat.

Now I reassembled everything and tested each gear as I put it in for smooth and easy rotation. I attached the side plates, pickups, and then the wheels, gauged them and again tested for ease of rotation. I did not replace the grease behind the wheels as there seemed to be no need for it after the plates were smooth and flat. Any grease here will only aid in the dust collecting process and that’s not something we intend to do on purpose. The plates are a copper colour after the filing and will have to be blacked again using some paint or a black felt marker. At this point everything should be relatively loose and easy to turn with no binding. It is time to mount the motor. I had to add no shims to the motor as the mesh with the gear was acceptable. Too much space between the worm and the gear make it run noisy and too little will show up any imperfections in the worm and gear causing binding, and due to the extra stress on the motor, overheating and burnout. To get the optimum adjustment I will hold the chassis in my hand while it is running and adjust motor up and down until the I get the quietest sound. This is the optimum mesh for the mechanism. Then shim to keep the motor in this position.

I then ran the mechanism slowly with out adding any grease. Watching to make sure I put everything together right. Then I add a little grease. I add the grease again by holding the running mechanism in my hand and slowly adding the grease to the running worm gear. This will automatically pull the grease into the gear train without getting it all over the chassis. Remember the only place grease does any good is between moving parts, not all around them.

Next come the siderods. Again deburr the holes as these pieces are also punched. Make sure the wheels are properly quartered. Attach the connecting rod between the wheels only, one side at a time and test run to check for binding, then the second side and run and check again. An hour or two of running with the siderods on will not hurt. Then reassemble the cylinder assembly with the remaining rods. Don’t tighten the screws too much here as a little slop is what’s needed for this type of mechanism to run well. Sometimes I will get a little squeak out of the valve gear on my HO locos and will add the tiniest bit of Remington oil only if I have to. Normally I will avoid adding oil to these areas as this is also a dust and lint collector.

I found on my mechanism that the rod end at the crosshead hits the screw on the driver every time it came around. This caused a bit of bumping along the track. I found that the cylinder assembly rotates a little bit on the single screw holding it on. I twisted the assembly a little bit and found a spot where the rod just clears the screw. I suppose if this doesn’t work you can file a bit off the head of the screws. Leave enough there so you can still turn it with the screwdriver.

Mine runs very smoothly now for hours on end at about 10 scale mph with out pulse power. At this point add some cars with a little bit of weight and let the little fella do some work. I used my newly built flat car with the Plymouth on it!

I will later on remove the plastic cylinder assembly and attempt to replace it with a scratch built one out of brass. This will eliminate the bulky look and hopefully produce a less finicky mechanism.

This concludes the first portion of my report and hopefully helps all of you tune your “Swiss watches”. Next time, assembling the basic brass superstructure of the Forney and mounting on the chassis.

Please, all criticism, good or bad, is welcome. Ask questions if you don’t understand something. It can only make me write better articles in the future.

Adios, Aufwiedersehen, Adieu, and happy modeling till next time

Joerg Seiler

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