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Author Topic: Steam loco 4-8-4 rebuild  (Read 1546 times)
crosswire

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« Reply #15 on: May 06, 2021, 08:43:09 AM »

The 2nd motor did not have caps.

When I disconnected the caps on the 4-8-4 motor, I only disconnected the cap wiring soldered to the motor frame. At this point, I could try removing the caps entirely.
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rbturner

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« Reply #16 on: May 06, 2021, 09:33:17 AM »

If you took the caps out of the circuit then I don't imagine they are causing the issue.

Back to the drawing board.

Did you check stall current at any point in this operation?
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crosswire

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« Reply #17 on: May 10, 2021, 09:40:09 AM »

The DCS52 reports amps at the control station to JMRI. When on the upgrade, train motion stopped, but drivers turning, the reported amps are 0.4 to 0.5. The decoder in the loco is rated at 1 amp.
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rbturner

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« Reply #18 on: May 10, 2021, 09:54:23 AM »

While watching the ammeter on your command station, what does it read when the loco does its random stops?

Back to what Jeff said about the decoder going into thermal shutdown, I would run the loco and pay close attention to what current it is drawing. If it is near the one amp rating of the decoder before it randomly stops then it would appear there is something causing current draw to increase.

It would then be binding maybe.  Very weird issue for sure.

The only other thing I have heard of causing stuff like this is when another throttle has the address of the loco in it and the two throttles fight over control.
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crosswire

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« Reply #19 on: May 13, 2021, 09:12:43 AM »

With this one loco running, the ammeter reads about 0.4 to 0.5 amps just before a stop. There is a time lag between the ammeter updates of a few seconds, due, I suppose to the time lag incurred between reading the current at the DCS and then displaying the reading on the laptop screen. During the stop, the ammeter reads 0.2 amps which seems to be the background load with no locos running. While this loco is stopped, the headlight is still getting power. The only time the ammeter reads close to 1.0 amp is when four locos are running.

I did read that loosening the screws that hold the frame, that holds the drivers and the trucks in place, helps the loco run better. I did try this with some success; so, I took the next step and removed the screws entirely. The loco did run much better; especially, on the curves. Better meaning the drivers slipped at a faster rate than before on the upgrade, but 4 cars was still the limit.

This particular model of the 2-8-2 has brake rods and shoes, attached to the frame, that drop down between the drivers. It is possible that the drivers, when under load up the grade, are rubbing against these rods and loosening or removing the screws holding the frame allows the rods to move out of the way. Needless to say, testing this would require the permanent removal of the rods and I am hoping to avoid that as I doubt I could ever get all eight of the rods glued on again.

As for the throttle, I only have one DT and it has not been plugged into the LocoNet while testing this loco.
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rbturner

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« Reply #20 on: May 13, 2021, 09:56:04 AM »

I would think if it is binding that is causing the loco to stop you would see increased current draw. You say it doesn't so I don't think that is the issue.

I have heard about and done the screw loosening thing with some success. Usually I will investigate what the cause is and file away some material to make it run well with the screws just snug; not honked down like the factory does.

I am stumped as to why the loco just randomly stops. You have swapped the decoder and have the same issues which makes me believe that the issue is in the loco which you have pretty much proven is OK.

I don't remember if your loco uses an 8 pin plug for the decoder install. I am wondering if it does, can you install the dummy plug and run the loco on DC to see how well it runs? Can you detect any slowing or other issues? I am wondering if it could be something funky in the motor.

The other thing that I would try is doing Internet searched for similar problems. This has helped me on more than one occasion.

Please, keep us posted as to what you are doing. These issues and their resolutions help the rest of us keep them rolling.
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crosswire

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« Reply #21 on: May 14, 2021, 09:07:08 AM »

I did not know that installing the dummy plug would reset the loco to DC. I will try that.

I had three of the 2-8-2s, one had a non-functional pancake motor and I gave up trying to fix that that one. the second loco had a burnt motor and that is the one we are working on. The third loco is still DC and I have run that one. It has the same motor and gearing as the one we are working on. It does not randomly stop or cause track faults, but has the same problems negotiating the 2% grade. It does not have the brake rods that the the second loco has.

I did notice, while checking the brake rods, that the drivers wobble a bit more on the second loco, the one we are working on, than on the third loco. The quartering seems OK, but maybe the driver shaft journals are worn and that is causing binding.

The new motor for the second loco was sold as being for a Niagra and came with suppression capacitors. It had the same dimensions as the old motor, but came with a flywheel and a different main gear. Due to space constraints in the chassis, I had to remove the flywheel. I installed the main gear from the old motor on the new one and the motor and complete loco bench tested OK. However, when I put the loco on the track and tried to run it, the random stops started.

I have not yet removed the caps, but will try to get to that today.
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rbturner

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« Reply #22 on: May 14, 2021, 10:45:48 AM »

I am glad that you are making some progress.

Something else I got to thinking about. What address are you running the start and stop loco on? I am NO DCC guru but have read about some addresses causing issues with the DCC 'wizardry'. Of course my old brain doesn't remember what these numbers are/were but maybe try a decoder reset and running it on #3.

I recall you were using Digitrax decoders and I believe to do a reset you program CV 8 to #8.
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crosswire

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« Reply #23 on: May 15, 2021, 08:44:19 AM »

When I replaced the motor, I had to modify the motor mounts  a bit. I found that the new mount had come loose and allowed the motor to lift a silly millimeter or so in forward, enough to disengage the gears allowing them to bind tooth to tooth and stall the motor. In reverse, the geometry of the gears pushed the motor back into place, so the loco seemed to operate much better. The random stopping problem appears to be solved. It is just regrettable that the loco is such a poor performer on a grade. Oh well.

rbturner - Thank you very much for your assistance with this problem. The answer was binding; I was looking in the wrong place.
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rbturner

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« Reply #24 on: May 15, 2021, 09:32:23 AM »

It sounded like binding but when you mentioned it was now running OK forward I figured we were barking up the wrong tree.

Glad you whipped the problem. Also nice to see you report what the problem was. We all learn by these things.
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crosswire

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« Reply #25 on: May 17, 2021, 08:27:45 AM »

Both the DC and the DCC 4-8-4s that I have are, apparently, weak pullers. By contrast, a Bachmann 2-8-2 and a Rivarossi 2-10-2 that I have can each pull 11 hoppers and a caboose up the same grade; albeit, with drivers slipping, but they make the grade, NPI. Maybe the difference in driver size or weight distribution causes the difference.
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jward


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« Reply #26 on: May 17, 2021, 09:25:10 AM »

My experience has been that a good, well designed diesel right out of the box will outpull most if not all steamers any day. I have several diesels, including the Bachmann FT and GP7, that will pull 20 cars up a 4% grade while my best pulling steam, a ROundhouse 2-8-0, can only pull 12. But still, I would have expected a 4-8-4 to do at least as well as the 2-8-0.
« Last Edit: May 17, 2021, 08:22:14 PM by jward » Logged

Jeffery S Ward Sr
Pittsburgh, PA
crosswire

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« Reply #27 on: May 17, 2021, 03:01:21 PM »

May be the 4-8-4s came in sets and are not the same quality as the non-set locos. These locos do not have speed or pulling power. I would have thought these locos would have had one or the other. The 2-8-2 pulls well and is one the fastest locos I have; just the opposite of the 4-8-4.
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rbturner

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« Reply #28 on: May 18, 2021, 07:21:06 AM »

Regarding pulling power; have you looked at the lead and trailing truck's downward pressures? I have also seen tender drawbars that lifted the rear of the loco. But I recall you saying that this isn't the case here.

I have seen some steam locos that had too much spring, downward pressure on the lead or trailing trucks that lifted the drivers a bit.

I don't recall right off how these are made so there may be no springs at all.
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crosswire

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« Reply #29 on: May 18, 2021, 08:03:50 AM »

Both trucks have springs; however, I did try running the loco with the trucks removed, no change in operation. I did try more weight and traction tires, but this improved traction enough that the drivers stopped slipping and the motor stalled.
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