# Bachmann "Centennial" Mogul gearbox disassembly?



## Tom Lapointe (Jan 2, 2008)

The oldest section of my Watuppa Railway's mainline runs right up against our chain-link fence (in fact, it's supported by it). The adjacent neighbors are people we've known & been friendly with for years.







They have a couple of little girls around 5 ~ 6 years old or so; about a week or so ago, they asked if I'd let them run a train.







I had a lot of equipment out that day, all Bachmann locos; 3 & 2 truck Shays, the 2-6-6-2T Mallet, & my "Centennial" Mogul. Wanting to be a "good neighbor", & figuring whatever I gave them was going to be run *fast, *I set them up with the Mogul on a short passenger train & handed them the wireless NCE ProCab over the fence. As I expected,







for maybe *3 minutes *the Mogul & it's train raced around the mainline (my trackwork is smooth enough that I wasn't worried about derailments) - then it suddenly *stopped. *







Taking the ProCab back, I went over to check the Mogul; & when I tried running it myself, just got a faint "click" out of it, *NO forward or reverse motion, & discovered I could now roll the loco freely by hand *







- pretty sure at this point they split the axle spur gear.









I've currently got the Mogul on the bench, inverted in my home-made loco work stand. The gearbox drives the center axle (which also has the eccentrics for the Stephenson valve gear on it). I've removed the bottom cover plate & have removed the main & piston rods from the drivers; I've got the axle loose but can't remove it yet due to the Stephenson linkages. Unfortunately, this is *not *one of the locos Bachmann has a detailed exploded .pdf diagram on line for yet; I've got the owner's manual but it only shows the major assemblies. Wondering if the drivers are held to the axles via screws under a cap? (& if I get the driver off the axle, is the axle keyed for quartering? - & how do I go about removing the Stephenson gear?).









Advice from anyone else who's disassembled one of these would be appreciated.







Tom


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## East Broad Top (Dec 29, 2007)

Yes. There are caps over the driver centers. Pop them off gently with a small flat-head screwdriver to expose the screws beneath. Pull the screws, and the drivers will slide off of the axles. They're keyed, and slide onto the axle via a plastic hub. Once the drivers are off, you can carefully lift the bearing blocks out of the frame (if you haven't done so already) and remove the Stevenson's valve gear. Do yourself a favor here and get a small clamp or tape or some means of keeping the valve gear and eccentrics together so each side comes off as one unit. It will make reassembly a WHOLE lot easier. Once the eccentrics and valve gear are off the axle, it's just a matter of replacing the main gear. 

When you open the gearbox, count the teeth on the main gear. According to Northwest Short Line, the 4-4-0 and 2-6-0 use a 24-tooth gear (NWSL part #2223-6). However, I've had a number of these gearboxes apart, and I have yet to encounter one that has a 24-tooth gear. They've all had the 25-tooth gear (NWSL part #2226-6; the 2-8-0 replacement gear). Count the teeth and order the appropriate replacement gear. 

*Here's a link* to instructions on Bachmann's web site covering replacement of the gear. (Note: there have been sporadic reports of an alleged virus on B'mann's web site, so if you're concerned about that, use a mobile device or a Mac to go to the web site.) 

Good luck. 

Later, 

K


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## Tom Lapointe (Jan 2, 2008)

Thanks, Kevin!







That's pretty much the information I needed.







The photo link you sent also looks helpful. I'll take your advice on the Stephenson linkages & put some tape or cable ties around them to hold them together before I try removing the axle. I've already removed the tiny screws that hold the gearbox halves together; haven't been able to open it enough to view the axle gear yet, but from what I can see of the intermediate spur gears, they look OK. The journal boxes are loose & ready to be slid out ot the frame (might have to unsolder the electrical pick-up wires from them, but that's not an issue for me). I should add that I think this is the absolute *first *time I've had any mechanical issues with this loco, it's been a reliable runner.









I also think that once I've got it repaired, I'm going to try to program an *upper speed limit







*into the DCC decoder (a Digitrax DG-583S). Come to think of it, that might not be a bad idea for *all my locos. *About the fastest I'll run this engine myself is what I estimate to be a scale *45 mph *(since I use it only in passenger or milk train service). It's not only in the case of kids running it again - I've often had to tell *adult *visitors I've let operate trains (especially the Shays!) to slow things down to scale speed!







*(Gee, can't it go faster than that







*). Thanks again for the help! 







Tom


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## East Broad Top (Dec 29, 2007)

When you get the gearbox apart, look at the main gear. If it's not cracked all the way to the edge, it may be possible to repair as opposed to replace. There's a narrow hub on the gear that's 3/8" outside diameter. If the outside of the gear is not cracked, you can get some 3/8" ID brass tubing and cut two thin slices to use as reinforcement sleeves. Pull the gear, degrease it, and apply some JB Weld around the hub. Slide the sleeves over the hub on either side of the gear, then replace the gear on the axle. From it completely stopping and free-wheeling, it sounds like it's a complete split, though. The gear on my 4-4-0 that was just cracked at the hub could spin, freely, but still had enough grip to where with a light prod would move for a few feet before spinning again. (I just JB-welded it back to the axle without the brass sleeves. Seems to have held up well enough in its own right.) 

With the NWSL Replacement gear, keep in mind that it's a bit thinner than the stock gear (it doesn't have the hubs the stock gear does.) I've heard occasional reports of people using the gear in their 2-8-0s where there's just enough side-to-side play in the gearbox once re-assembled that one of the bronze bushings for the axles come loose into the gearbox. When I did my 2-8-0, it seemed okay, but if you've got some very thin washers with 1/4" openings (mine like that are typically liberated from electrical toggle switches), you might want to put one in there as a spacer. I've not put the NWSL gear in the 2-6-0 gearbox to check on lateral play, but given that both locos (the 2-8-0 and 2-6-0) appear to use the same gear and the same replacement gear, I'd presume the same caveats apply. 

Oh... one more thing... If you've removed the little pins that hang down from the center drivers (pseudo-flanges) because--let's face it--they just get in the way, while you have the axle apart, cut a thin slice of plastic tubing to use as a spacer to reduce the lateral play of the axle in the frame. A Bic pen barrel works well. I think on mine, I cut the slices to a bit less than 1mm each. This keeps the blind center driver from being able to move too far sideways to where it might fall off the railhead when going around particularly tight curves. If you've not had that problem, then you may not need to worry about it. I did it as a matter of course when I removed that "pin plate" from the gearbox, so I don't think I've ever run without them to make any comparison. 

I hear you on the top speed setting. On my railroad, my locos are programmed for a top speed around 30 mph, though anything more than 20 just "looks" fast when it's running in the garden. 

Later, 

K


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## Tom Lapointe (Jan 2, 2008)

Hi Kevin,

Just finished completely removing the axle & disassembling the gearbox a few minutes ago (the advice on the Stephenson gear was well heeded - used very small cable ties around the links, then passed a short piece of wire through the outer washer & eccentric axles holes, twisted the wire ends to hold everything together in the proper order).

The axle gear (which is as you said, 25 teeth) is split in 2 places, 1 split clear to the rim. Another possible fix might be try to weld the plastic back together with a soldering iron, but considering the project this loco is to take apart (& will be to properly re-assemble!), think I'll splurge the $12 + shipping for the new NWSL gear. 

Thanks again for your help. . (Replying from my iPad, so can't get too fancy with fonts & emoticons here!). ). Tom


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