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Discussion Boards => HO => Topic started by: crosswire on April 22, 2021, 01:29:28 PM



Title: Steam loco 4-8-4 rebuild
Post by: crosswire on April 22, 2021, 01:29:28 PM
Hi,

I have a 4-8-4 that needed a new motor, DCC conversion, and traction tires. I have all the work complete and the loco works great in reverse. However, in forward, I get numerous track shorts on the DCS52 command station. Monitoring volts and amps in the DCS with JMRI, no low voltage or over current is indicated.

The loco also runs well on level track, but not forward, and not upgrade. I tried changing the decoder with no success.

Any ideas about what is going on would be appreciated.

John G.


Title: Re: Steam loco 4-8-4 rebuild
Post by: RGW on April 26, 2021, 07:08:37 PM
Do you have a way to run it on dc with out the decoder. This way you can check to make sure it is not some mechanical problem. For example something in the valve gear. I have had many problems only to find some thing simple like a tiny part or screw binding .

Help this helps


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on April 27, 2021, 08:46:10 AM
RGW, thanks for the suggestion, I can give that a try. All this work changing and removing decoders is great practice on soldering. But, I certainly need that anyway.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on April 27, 2021, 02:49:55 PM
Going, back to the original question, restated, concerning multiple track faults: can an overloaded motor cause a track fault even if a volt meter shows 13.8 volts and the ammeter shows 1.4 amps on a DCS52?


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on May 02, 2021, 09:37:10 AM
After a complete rewire, most of the track faults have stopped; however, sometimes the loco just stops at random locations for no apparent reason and will not respond to commands even though the headlight indicates the loco has power.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner on May 02, 2021, 10:00:21 AM
A couple of thoughts;

sometimes a headlight, which only requires a minimal amount of current to operate will work fine while the motor which requires maybe a half an amp will not run.

This reflects a questionable connection between the wheels and track.

When there is  a wiring fault someplace a voltmeter may still show voltage present but not 'enough' current available to do any work.

I know you have re-wired recently so we'll assume that you whipped any wiring issues but maybe there is still some oxidation on the rails/wheels.

Hope this helps.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner on May 02, 2021, 10:13:44 AM
I forgot to ask if you got the loco to run OK in forward?


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on May 02, 2021, 10:44:45 AM
The loco runs forward ok, although 4 passenger cars or 5 freight cars up the 2% grade is the max it will do. Seems strange to see a 4-8-4 with an 8 axle tender barely making the grade with 4 or 5 cars. Oh well. This is with clean track, clean wheels and a lube job.

The problem now is the random stopping and related loss of control. The loco will make several circuits of a loop and then, just stop in no particular place. The fix is also random; sometimes, initiating a track fault near the loco will clear the problem, sometimes changing to a different loco on the DCS52 and then, changing back clears the problem, and sometimes waiting overnight does the trick.


Title: Re: Steam loco 4-8-4 rebuild
Post by: jward on May 02, 2021, 11:39:22 AM
This sounds like a decoder going into thermal shutdown. It;s the decoder's way pf protecting itself from heat damage. WHat decoder did you use? Apparently, the motor is drawing more current than the decoder can handle. This and the sluggish performance of the motor lead me to believe you have a bind somewhere that is making the motor work alot harder than it should.


Title: Re: Steam loco 4-8-4 rebuild
Post by: RGW on May 02, 2021, 01:21:49 PM
This was my thought. If the is a mechanical problem it can cause a  electrical problem. Just curious  did you say the engine was running at 13 volts this seems high to me as at full power with a train  the drivers should be slipping or the motor will start running hot.

Just a thought. However I have very  little DCC experance my self.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner on May 03, 2021, 09:47:02 AM
Crosswire, it's hard for us to really help you because we are not onsite to see the goings on.

It sounds like you have a real stinker of a problem. I wonder why it isn't pulling better?

Something that I just thought of and maybe you already checked this; but I have run into poor pulling caused by the tender, lifting the rear of the loco up.

Is there any chance the drawbar or wiring is binding any at all? This can lift the rear on the loco up and kill traction.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on May 03, 2021, 11:28:41 AM
Thanks to Jeffery, RGW, and Bturner for your questions and suggestions, all good points.

I did remove the traction tires to allow the drivers to slip and the motor to keep running. After about 30 minutes of running with 4 cars and the drivers slipping, the motor was barely warm.

If I remember correctly, the 13 plus or minus volts is what JMRI reports as track voltage at the output terminals of the DCS52, not the decoder output voltage.

The decoder is a Digtrax DH165A0 mounted in the boiler, so no wires to the tender to lift the rear of the loco. The tender attaches to the loco with a vertical pin on the drawbar that fits into a transverse slot in the rear of the loco. This pin was too long and was causing the tender to derail. The pin has been cut off and no longer interferes with either the loco or the tender.

As for mechanical binding, there are no unusual noises or "jumpy" operation and the loco runs like a rabbit on a 2% downgrade, even with 8 cars attached, so I would not expect any binding.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner on May 04, 2021, 10:21:45 AM
I re-read this whole post and the only thing I can come up with at this point is to wonder if maybe you have a funky decoder.

I put a Digitrax sound decoder in a loco once that did the same thing as you described. The engine would run fine then slow down and stop.  Then it would take off again. I considered it being a thermal shut down but the locos stall current was tested prior to the decoder install and after the install, track current was monitored with a meter. Current draw remained well below the decoder's rating.

You mentioned replacing the motor. Did the replacement by chance have noise suppression capacitors on it? I have read that the caps can affect the decoder's back EMF feature and they recommend you remove the caps from the motor.

Obviously none of this would affect the pulling power.



Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on May 05, 2021, 04:06:00 PM
The decoder was changed to another DH165A0; the problem persisted. I installed the used decoder in another loco, which has not experienced any problems.

The motor does have RF suppression capacitors, which may explain why the various changes I tried to CV 57,56, and 55 had no apparent effect. I did disconnect them at one point when the loco had traction tires to see if they had an effect on the motor performance. As you mention, this had no effect on the pulling power.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner on May 05, 2021, 08:28:36 PM
Did the motor in the #2 loco that got the first decoder and ran fine have the suppression caps?

I am guessing not and would think the thing to do is cut them off of the 4-8-4 and see what happens.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner 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?


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: jward 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: rbturner 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire 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.


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on June 13, 2021, 09:09:28 AM
I am still working on this loco and have eliminated or corrected all the suggested problems. I have discussed the decoder and its tuning with the folks on the Digitrax forum.

However, the performance problems remain.

Bach Man - is there a possibility that the original motor, 1999 or 2000, had different specs than the new Niagara motor I purchased for this loco?

Thanks,

John G.


Title: Re: Steam loco 4-8-4 rebuild
Post by: the Bach-man on June 13, 2021, 10:53:59 PM
Dear John,
This loco has undergone continuous upgrades since it was introduced decades ago.
The latest motor is very likely improved since 2000.
Good luck!
the Bach-man


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on June 14, 2021, 09:32:32 AM
Thanks for the reply Bach Man,

So you are saying the new motor should perform better than the old one. Does this mean that the new motor should have the same or better torque output and the same or better rpm range? I have looked for these specs and could not find them.

Regards,

John G.


Title: Re: Steam loco 4-8-4 rebuild
Post by: jward on June 14, 2021, 10:02:05 AM
Keep in mind the motors would not be the only improvements made over the years. The drive train may be improved as well, with unnecessary friction engineered out of it. AS I've mentioned before, I have several Bachmann locomotives that will pull at least 20 silver series freight cars up a 4% grade with 18r turns.
 


Title: Re: Steam loco 4-8-4 rebuild
Post by: crosswire on June 15, 2021, 08:52:52 AM
Jeffery,

Hi jward,

I also have some locos, by Bachmann and others, both steam and diesel, all of which have been converted to DCC by me, that can pull cars over the 2% grade on my layout. These locos include one Bachmann 4-8-4, converted a couple of days ago. However, the Bachmann 4-8-4 under discussion can barely pull itself a 4 cars over the grade.

The question is why not this one? The chassis, drive gearing, and running gear on both 4-8-4s are the same vintage; thus, any recent upgrades to the running gear do not apply. The only difference is the motor. I am waiting for Bach Man to advise if there have been any rpm or torque changes changes to the new motor. He did indicate improvements had been made, but did not indicate if the improvements made changes to the motor torque and rpm ratings.

The primary drive gear on the NIagara motor is much smaller in diameter than the older gear. Assuming the gear changes did not affect the final speed of the locomotive; either, the motor rpm and torque had to be changed or the intermediate gearing was revised.

I choose the Niagara motor for my upgrade as it was the only one I found that was the same size as the old one. I could not find any torque or rpm specifications for either motor, so I took a chance that the Niagara motor would work. If this was a bad decision, I would like to know, then I can put this loco on display.

Thanks for the response,

John G.