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Tuning tips for the Bachmann Plymouth

From Jeff, 14 Jan 2005

Hey guys,

Just thought I’d share a few tuning tips that I used to tune my two (new version) Bachmann Plymouths.

I received my new gems from Big Al/B&F yesterday. I test ran the first and was pleasantly surprised at how well it ran right out of the box. For a $25 locomotive and one that has no flywheel, it ran very smoothly with no breaking in.

Being ever the curious mechanic, I took it apart this afternoon to examine “the guts” of it. I erroneously told Al last night that the gear ratio was about 40:1 based on the gear layout on the instruction sheet. Well, upon disassembly I found I was incorrect, or at least the graphic representation of the gearing in the instructions is wrong. The actual gear ratio is about 24:1, which given the small driver size is not so bad.

I pulled the motor out of the frame and reassembled the frame to assess the smoothness of the gears. I noticed a very minor binding in the gear train, so I disassembled the mechanism again to try to find the bind and fix it.

I found that the two “pegs” or cast shafts for two of the gears, that are integral to one half of the frame, had some burrs on their ends. This is a minor problem because the shafts are shorter than the thickness of the gears, which produces a very slight drag on each gear. I removed the burrs on each shaft using a very fine needle file to file a very slight chamfer on the ends of each shaft. You must be very careful NOT to slip with the file and score the shaft!

With that done I looked for more sources of binds and found that the worm gear (the double gear that mates with the worm on the motor shaft) still bound slightly when rotated with my finger. By pressing on the side of the gear I figured out that the gear was ever so slightly catching on the flat surface that it was contacting (the side of the gear). A few careful swipes with the needle file chamfered the sharp corners and eliminated the bind.

The last step was to chuck a stainless steel wire brush in my Dremel tool and polish both shafts and any surface that they run against on the metal
part of the frame. Check the gears on their shafts again to ensure they run smoothly. Mine showed a noticeable improvement in smoothness over the “stock” condition.

I gently cleaned both frame halves and the two gears with some denatured alcohol and a stiff brush, then after blowing them dry, I reassembled the mechanism. To my disappointment the mechanism barely ran. After some troubleshooting, I realized I had re-installed the delrin frame spacers that the coverplate screws into, upside down. This effectively lowered the coverplate, tightening up and binding the axles against the metal chassis.

After fixing the problem, I test ran the mechanism ran better, but still not as well as it did… A little more troubleshooting showed that the bottom cover plate MUST be a little loose to allow the wheels/axles to turn smoothly. So, I tightened the screws up tight, and then backed them off about 3/4 of a turn. Back on the test track and the mechanism ran EXTREMELY smoothly!!! Even at very slow speed. The improvement in running quality over “stock” was noticeable. My mechanism crawls so slowly you can count the ties with ease and no sense of urgency. After a little test running, I
applied some Labelle plastic compatible gear oil (the thicker version). It’s now been running for about an hour at minimum speed pushing a few ore cars and a Minitrains coach with no sense of hesitation or binding.

As a benchmark, I test ran the Plymouth against my LL SW9 mechanism, and the Bachmann Plymouth’s performance after tuning was BETTER than the LL SW9, and that engine was heavily broken in!

Hope that helps…

Jeff

A few more things on tuning the new version of the Bachmann N scale Plymouths…

The gear oil I specified in the last message was Labelle #102 “Gear oil”.

I also used some (lighter) Labelle #108 “Lubricating Oil” for bearing lubrication. I lubed the motor shaft bearings front and rear, as well as lubricating all the axle shafts.

The combination of a better motor, smoother gearing and more weight make this a great running little critter mechanism. I was very surprised it ran as well as it did, and it does it WITHOUT a flywheel!

I encourage any of you guys out there interested in having a good running critter to purchase one (or more) of these locomotives if you haven’t done so already. They are a bargain and great value, and Big Al has them in stock, for a very reasonable price.

On another note… I spent some time looking over my mechanism with an eye toward making it four wheel instead of the stock six wheel. It would be easy to do, but yet it wouldn’t be. To make the conversion, you only need to remove the wheels from the axle gear. Therein lies the problem! The wheel and stub axle are all one unit. Pressing them out would be interesting… The other issue is that the axle rides in the frame/mechanism on the metal stub of the wheel/axle assembly. To make this a four wheeler, you’d have to remove the middle axle, somehow separate the wheels/axles from the plastic gear “muff” (in UK modeler parlance), turn off most of the wheel itself, then reinstall. Not so easy!

For now, I plan to leave mine as 0-6-0′s…

Have fun!

Jeff

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