benshell

Upgrading an AML K4

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benshell   

Two years ago I bought an electric AML K4 Pacific at a swap meet, as an open-box item without factory smoke unit or working lights, knowing also that these locomotives are known for running too fast with a motor than can burn out with too much load.

 

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Now this locomotive is finally on my workbench, and the first thing I want to do is upgrade the motor. Greg Elmassian has a documented some possibilities on his site, as well as providing some tips on disassembly which were very useful, however none of his suggestions seemed perfect.

 

The stock motor is a Pittman GM9234S017-R1, 24 VDC, 11.5:1 ratio. One suggestion on Greg's page is a GM9413-2, with a 19.7:1 ratio. This sounds perfect and it's the same physical size, but in studying the specs for torque and current it appears to be a less powerful motor than stock. Perhaps the gearboxes would be interchangeable, since it's the same physical size, but that's a big risk considering the cost of motors and the factory motor isn't exactly ideal either.

 

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So after much research, including other brands and sizes, I've decided to try a Pittman GM9236S020. I found it on eBay for only $30 + $7.50 shipping. It appears to be ideal in terms of the specs: 19.7:1 ratio, speed of about half the stock motor, and about 2.5x the torque of the stock motor. The current requirements are a bit high with a stall current of 9.64 amps, but I've got a 10 amp QSI Titan DCC decoder for it, and the continuous current requirements should be much less, with the sweet spot of the speed, current, and torque chart at about 5 amps: https://www.servo2go.com/support/downloads/GM9236S020.pdf

 

The downside is that this motor is 0.65 inches longer than the stock motor, and I don't think it's going to fit without some additional work. There is a little room between the motor and the backhead (although difficult to measure), but I'm estimating more in the 0.3 to 0.4 inch range. However, I can't see any reason why I can move the motor forward a little. I think I can modify the motor bracket, and cut off a little of the shaft to the axle gearbox which has a universal coupling (and I don't know why, since the motor and axle gearbox are both fixed, unless it was just to made the design of the motor mount easier so it didn't have to align perfectly.)

 

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The new motor will arrive sometime next week, so I will resume work on this then.

 

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Chuck   

Before you modify anything I'd try the motor first and run loco with boiler off. I tried a 19.7:1 motor in the last K4 PS3 conversion I did last fall and the loco was way too slow. Could only get like 60 mph out of it at 30V on track. I stuck with the stock gearing.

 

Changing motor gearboxes is a pia as armature shafts are different sizes where the pinion gear presses on.

 

I've converted 5 of these K4's to PS2 & 3 and only had 1 that ever overheated the motor. What I did was eliminate the weights that are on either side of the motor to allow more air to move around in hopes of keeping motor a bit cooler.

 

Hope that helps a bit.

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benshell   
36 minutes ago, Chuck said:

Before you modify anything I'd try the motor first and run loco with boiler off. I tried a 19.7:1 motor in the last K4 PS3 conversion I did last fall and the loco was way too slow. Could only get like 60 mph out of it at 30V on track. I stuck with the stock gearing.

 

Changing motor gearboxes is a pia as armature shafts are different sizes where the pinion gear presses on.

 

I've converted 5 of these K4's to PS2 & 3 and only had 1 that ever overheated the motor. What I did was eliminate the weights that are on either side of the motor to allow more air to move around in hopes of keeping motor a bit cooler.

 

Hope that helps a bit.

 

Good tips, Chuck, thanks! It's good to hear from someone who's worked on these engines! I did run on DC on my workbench and it does feel really fast. I suppose a quick and dirty DCC install would be easy now that I've opened it up (I don't have a way to run DC on my layout).

 

I do want a lot of power though. I have a long 2.5% grade, and I like to pull long trains. In fact, I've also ordered some additional lead weights!

 

Do you know which 19.7:1 motor you used? If it was the GM9413-2 then it has a no-load speed of 142 rpm, compared to the stock GM9234S017 speed of 424 rpm. The GM9236S020 motor I've ordered is rated at 236 rpm, so I'm hoping it's a good compromise. But in any case, I prefer power to speed, and when I'm running multiple trains on one continuous loop the freight and passenger trains need to go the same speed. (I also don't have any PRR passenger cars yet, so for the time being this will have to be in freight service.)

 

I also thought of one more potential way to fit the bigger motor in there: I'll have to open up the gearbox to verify, but I opened the factory gearbox and there's a lot of extra space! It might be a pain, but I could potentially shorten the gearbox. Machining down the housing would be easy on my lathe, but removing the shafts to shorten them might be tricky.

 

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Chuck   

Ben, I tried a GM9213-2 motor....just something I found on eBay with correct gearing. The motors are serviceable if they have ball bearings. The bronze bushed motors are something else as the bushings are sort of self-aligning and staked into the end covers which makes dis-assembly about impossible...like in removing armature without removing pinion.

 

Be real interesting to see what you come up with! With stock motor I can hang like a .200" thick flywheel on the brush end and the firebox will just fit around it.

 

I don't envy you as those are the worst locomotives to open up...design wise. :angry:

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benshell   

After a nearly two week wait for the new motor (FedEx has seemed especially slow lately), followed by some other priorities, I'm back to working on the K4 for the moment. Today I did a test run with the new Pittman GM9236S020 motor, hooked up to the QSI Titan. Before going through a lot of effort to modify the locomotive and/or motor, I figured I should make sure I'm happy with the speed and power draw of this motor. I used a lot of electrical tape and rigged up quite a contraption, with my multimeter measuring the current. 

 

The test was mostly successful. I'm quite happy with the top speed (maybe not prototypical for a passenger train, but faster than I normally run trains). And the current draw was only about 1 amp, pulling 8 cars on level track. Although I'm not sure I'm measuring the amps accurately, considering PWM/BEMF, however I am using an RMS meter if that makes any difference. If I hold the locomotive back, the drivers just spin, pulling about 1.5 amps. If I also push down on the engine, I was able to see power draw up to 2.5 amps, while the wheels continued slipping. I'm sure I could force a stall if I really tried, but I put more pressure on the locomotive than any amount of weight I could possibly add!

 

The problem today was that at low to moderate speeds the engine wasn't running smooth at all--worse than I've ever seen. I will have to put the engine back on the workbench on rollers and see if I can improve this. I have to admit that I really don't understand motor PID settings at all, so there is certainly room for improvement. It doesn't have to be perfect, but it has to be better than the start you see in my video!

 

(My kids picked the cars--but they are more prototypical for the era than a boiler-less, cab-less steam locomotive!)

 

 

 

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Chuck   

Great news and I'm sure you'll get the decoder dialed in!

 

BTW....Nice looking layout you have there!

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benshell   

I knew it'd been awhile, but I can't believe it's been two months since I've updated this thread! I finally got back to making the new motor mount, and shortening the drive line, so now I'm ready to start reassembling... I did label most of the parts, but should have taken even more photos!

 

Here are photos of making the new motor bracket, and the completed drive line running on analog DC.

 

I started with a big piece of 1/8" steel. The original bracket seems to be brass, but that's more expensive and I want to add weight anyway.

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After some work on the bandsaw and a lot of milling on my LMS mini mill (light cuts in steel), I got the rough shape cut out:

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I did the round part as I often do on the mill, turning the part back and forth using vice grips holding the part over a 3/16" steel rod:

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I used a 4-jaw chuck on my lathe to hold the part for boring:

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I forgot to show the 1/8" slot I milled to make the bend easier to make, and in the right place, but I was so relieved when it worked. I did the same (but 1/4") for the second bend (as I had to drop the motor down to keep the same axial alignment).

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Here's the part test fit to the locomotive once I cut off the excess, drilled holes for the motor using the original part as a guide, and drilled and tapped 4-40 holes. The original is attached from the top, but I've drilled out the frame instead because it's far easier to attach this way. There wasn't room underneath for the screw heads to re-use the front two holes, so I've just used three screws instead.

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Finally, I had to shorten the driveline. Here's the original as I measured it. I found I only needed to cut off about 3/8" even though I moved the motor forward by more like 5/8", since there is a lot of play in the u-joint. and how far it slides onto the motor shaft. It was pretty easy to shorten on the lathe, and re-drill for the set screw in the mill.

 

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All assembled, it seems to run pretty smoothly:

 

 

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I stayed away from this engine with all the comments I heard about it's motor having problems. It is always cool to see someone overcome any issues. It almost seems like it's a part of being in G scale.

Of course there are plenty that just complain. They make posts like these, all the better. Nice work!

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benshell   

Thanks Ray, Chuck, and Joe! You guys all do so much work yourselves with upgrading, modifying, and kit-bashing equipment that you're an inspiration to tackle stuff like this.

 

So this evening I started reassembly and I've got the chassis all back together--gearbox cover, electrical pickups, brake hangers/pads, trailing truck, axle box retaining plates, and lead weights. But then I tested it one more time and it didn't seem quite as smooth. I can't figure out why any of this would affect the motion, as none of this makes contact with the wheels except the electrical pickups and it seems like they should cause consistent drag. It's not that bad though... not compared to my Aristo-Craft Mallet and it still seems to work okay. But, I'm looking for all the performance I can get out of this one. Any ideas?

 

 

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Turn the flywheel by hand while checking the side rods to see if they overly tighten up in any position.

If one does, try taking that side rod off and see if she runs smooth.

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Chuck   

Damn nice machining work! I esp. like the turning the piece in the vice while the mill is running...I never would have thought of that!

 

I've had that same problem before. Mine was once the the bottom "covers" are installed, that compresses the sprung drivers and tightens up tolerances. Adding the power pickup brushes creates drag and the two combined (that is covers & brushes) "tightens" up the drive and exposes all problems. Could be a quartering issue with one axle, or connecting rods not all the same length. Accucraft did have problems with the u-joint design as it's known to bind. I had 1 K4 where if I turned the axle gearbox around it ran great.

 

 

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benshell   

Thanks guys.

 

Chuck, yeah I never would have thought of turning the workpiece by hand with the mill running either, until I saw someone else do it! One of these days I'd like to upgrade my mill to CNC--it's just time and money!--although I'm also partly worried that CNC will make some operations more difficult.

 

Today I removed the side rods, and without them the center (powered) drivers run perfectly smooth. But with the side rods off the other drivers roll smoothly by hand--at least somewhat so--but with the electrical pickups they don't exactly roll freely. And the side rods seem to fit well. But they must be binding slightly somehow, maybe as Chuck pointed out in combination with the pressure from the bottom "covers" being installed things have just tightened up a bit. I don't feel like working on this anymore right now, so I'm going to try and finish reassembling and installing the DCC decoder and see how it runs. Maybe it'll run well enough, and break-in with time as Sean suggests.

 

The locomotive is so difficult to open that I've decided to put the decoder in the tender, with one 2" speaker in the boiler, and a 3" in the tender... only problem is that I forgot about a speakers until a week ago and they won't arrive until Monday. But today I did all the wiring to the tender, so I should have this wrapped up within the next few days.

 

(I'm suddenly motivated to finish quickly because I'm hosting a garden railway open house a week from Sunday for a combination garden railway club and Ford Model "A" club tour. I was just thinking it would be nice to run something new that happens to be a Model A era locomotive.)

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Chuck   

It just might wear in and run great! 

 

Model A club tour & garden railway open house...sounds like fun! :) 

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I've always wondered if MTH has their side rods so loose on purpose to help with things like this?

I got an O scale Sunset Niagara that had an axle slightly out of quarter. Being a novice, I enlarged the side rod hole to help the engine run smoother at slow speeds.

It would have been better to fix that axle. I took the quick way out. It's still not perfect.

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benshell   

Hi everyone, I've been behind on the updates here, but the story continues...

 

I (barely--the night before) finished installing DCC for my June 25th open house and (mostly) put it back together to run. I ran the locomotive a few times around the track, pulling 10 cars. It was running well, except that the chuff sync was WAY off (I accidentally calibrated it for 4x the correct number of chuffs!), until it slowed to a stop! Looking into the engine from underneath, it appeared that a wire had gotten twisted around the motor shaft. So back to the workbench it went.

 

Over the next couple weeks I opened it up again, did a better job with my cable management, fixed the chuff issue, thoroughly tested on rollers, and then fully reassembled. I also added more weight. Last weekend I tested again, pulling 18 cars quite well (no wheel slip). I was about to take a video, when, once again, it slowed to a stop and wouldn't budge! :(

 

This week I've disassembled again... more than ever before... and found the motor shaft complete frozen in the gearbox bushing. I've never seen anything like this. First I tried using my lathe chuck + vise grips and I could barely turn the bushing, but couldn't remove it. I ended using my 1 ton arbor press and it was really tough to remove! I did some polishing of the shaft in my lathe afterwards and there are some pretty big scars left (picture shown), but the bushing is free now.

 

However, I don't want this to happen again. I texted a machinist friend today and he said it was lack of lubrication. I did lubricate before I reassembled the first time, but I was running the engine pretty hard. Clearly I need to do something to solve this, so with my friend's advice I've ordered a Needle Roller Bearing, part # HK0509, with 5mm ID, 9mm OD, 9mm width. Next up, I will have to make an all new bushing to fit this bearing.

 

I do enjoy the challenge of doing stuff like this, but I keep thinking the project is almost done! My USA Trains Big Boy runs so smoothly and pulls so well (that's my reference point) and I just really want another steam locomotive that's comparable (but smaller and easier to carry!).

 

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I'm sorry to see that you had this trouble.

I have been leaning towards the use of roller bearings in more apps. I love them in the trucks of cars as it helps the engines that have to work out in the elements. I believe that even though these are models, they still endure some heavy work loads. So adding bearings just makes sense to relieve the engines of extra work. I imagine that in the summer heat, more stuff can go wrong. We sit in a chair in the shade, unaware of how hard these trains are working as they labor around the yard.

 Anyways, great work and thanks for sharing! I still wish I had bought one of these.

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Chuck   

Needle bearing in there will be great! Glad to hear that the open house/ car show went smooth!

 

I have a USA SD70 that was doing about the same thing...that is 1 drive would start squeaking. Take it apart and oil the armature shaft support bronze bushings and it would stop for about 3 hours then start squeaking again. Make a long story short I had to polish the armature shaft & extended armature shaft/ drive shafts, lubricate and now all is fine...I hope :mellow: 

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benshell   

Chuck, I will have to take a look at my USAT SD70s... I think one of them has also starting squeaking. Thanks for the suggestion!

 

Joe, that's my thought as well. There are a lot of forces at work here, and if my motor alignment is even a thousandth off (likely!) it would have made this problem worse. I'm hoping roller bearings help.

 

I wish I could say I finished the roller bearing assembly and tested this weekend... but just machining the bearing housing took all my limited shop time. I guess I also took the time to draw up the part in 3D and make a drawing (attached as a PDF), using Autodesk Fusion 360. I've been learning this program lately and I've been really impressed. Now I just need to press in the bearing and install. I guess I'm a bit hesitant on pressing in the bearing as there's no removing it (at least without destroying the part). I also realized that the bulky size of the new bearing housing is going to interfere with some supports for the electrical pickups. Oops. I guess I have another modification coming up.

 

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K4 Bearing Housing.pdf

 

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benshell   

After a month off for traveling and insanely hot weather making work in the garage/outside miserable, I'm back with some exciting news and a video to share! I pressed in the rolling bearing and reassembled, and the K4 is running smoother than ever! But just in case, this time around I didn't test run first... I took this video on the very first loop around the track with the new bearing! 20 cars was no problem until the entire train was on my 2.5% grade... then I had to lighten the load to 16 cars. I could probably add a little more lead weight to improve traction, but I probably won't bother for now. I just wanted another smooth running steam locomotive that could pull a decent train, and I feel I've reached that goal now. Also, it's running at top speed, which is about 20 volts DCC. A prototypical passenger train should run a little faster, but this is faster than I run most of my trains so I'm happy with the range. I guess the next step is getting PRR heavyweights. I'd been on the lookout for Aristo-Craft cars, but at this point I'll probably wait for the new USA Trains heavyweights. In the meantime, the K4 will be engaged in frequent freight service.

 

 

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