benshell

Upgrading an AML K4

8 posts in this topic

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.

 

IMG_1018.jpg

 

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.

 

IMG_0273.jpg

 

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.)

 

IMG_0274.jpg

 

IMG_0275.jpg

 

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

 

Share this post


Link to post
Share on other sites

Great work Ben, I look forward to hearing how things progress. :)

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites
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.

 

IMG_0286.jpg

Share this post


Link to post
Share on other sites

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:

Share this post


Link to post
Share on other sites

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!)

 

 

 

Share this post


Link to post
Share on other sites

I wonder if the meter is showing where the voltage drops on the layout slightly (current goes up)? It seems like it is touchy to that?

Share this post


Link to post
Share on other sites

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

 

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

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now