GP40 Smoking Motors & Debilitated Wheels

Aristo GP40 problems - Smoking motors & Debilitated wheels!
Ted Doskaris
January 31, 2010
Rev. GE-B

December 28, 2011
Rev. GE-C; corrected semiconductor stale link, added replacement motor material, added videos

October 11, 2017
Rev. GE-C1; repaired broken links, including embedded video

May 7, 2020
Rev. GE-C2; repaired broken link

As of this writing I have accumulated 10 Aristo-Craft GP40 locos. I got most of them in 2008. I did get an additional Rock Island GP40, road number 395, late in 2009, and in year 2011, I got the fourth Rock Island road no. 378 unit and then one BN unit.
I like the GP40s as they are nicely detailed locomotives, and when I first operated them they ran well, were very quiet, and drew little current.

For an overall description, see  Aristo-Craft GP40 4 axle locomotive vignette .

However, as time progressed problems started to arise. One of them developed total motor failures - which makes one wonder if and when some of the others may eventually do the same.

Since I currently have about 52 various locos (50 Aristo), many are not run that much until some passing in time. Also, being distracted for the last few years on house construction projects has delayed train running some, too.

For those GP40s I have with enough run time, they suffered from degraded wheel surfaces adversely affecting track power operation. But run time on these was only within about 100 laps on my under house layout - having then noticed wheel problems.

The following is a description of the problems:

Motor block shorted power pickup wires:

Rock Island GP40, road no. 392

The GP40 motor block has four wires with two black wires dedicated for power pickup originating from the wheels that contact the rails. The motor block wires pass through a rectangular slot in the loco's chassis. The chassis is plastic, but the interior upper part includes a long metal channel.

When the truck pivots, the motor block wires can rub on the metal edge of the slot within the upper part of the loco as shown below:

This resulted in smoke and melted insulation as the conductors within the two black wires apparently made contact with the metal that shorted the power picked up from the wheels.

Ultimately the 10 amp fuse was blown in the Aristo track side Train Engineer receiver that is used in my under house layout.

(By happenstance, the loco's Poly fuses were of no protection as the truck with the shorted wires was not in their electrical path for this circumstance.)

Though the slot in the metal section is larger than the plastic slot - a good thing - it became evident that this is inadequate to prevent the wires from abrading as I found the metal edge to be rough to the touch.
When the wires move back and forth against the edge as the loco truck pivots it's only a matter of time that they are sawed through. Depending on how the wires may be dressed, it would seem other locos that have the same type design for the slot opening would be similarly jeopardized.

To prevent the wires from abrading again, I used duct tape wrapped over the edges of the slot as shown below:
A more professional fix may be to use something like "cat track" to surround the edges.

Other Aristo locos may have a similarly designed slot, so it is advisable that the Aristo factory employ a similar preventative measure around the opening.

Failed motors:

I typically run two or three locos coupled together to pull a train on my under house layout.

In the case of two relatively new Aristo Rock Island GP40s, I had two of them running together pulling a train from time to time.

Since I have about 50 locos, the run time on many of them is not particularly much even though I may have had some for a long time.

Anyway, the Rock Island loco previously described with the shorted power pickup wires eventually suffered from two failed motors in rapid succession. The motor blocks actually emitted smoke as they drew excessive current!

At first impression one would think it had to do with the shorted power pick up wires, but this was not the case. If anything, shorting the power pickups would somewhat emulate what the over voltage protector IC provides in the way of protection by shunting current around the motors.
In this regard, the GP 40 includes a "surface mount" IC device (SMA33JC Transient Voltage Suppressor) in each motor block on the underside of a little circuit board. See below picture.

The SMA33 TVS device specs. include a nominal breakdown voltage of 33vdc and maximum surge current of about 8.5 amps. For direct download of 1SMA5.OAT3 Series data sheet that includes the SMA33 device, click on  On Semiconductor company data sheet.

I moved the failed loco to my loft test track area to do an evaluation.

My test track apparatus includes an MRC brand Control Master 20 regulated power source for the Aristo-Craft model ART-5401Train Controller having a "speed" knob for its output control. Also, included in this setup is an analog ammeter to monitor current. The MRC power source includes a mode switch for "Nudge" and a switch for "HO/N" or "G scale" voltage values. The "Nudge" function is meant to provide a pulsed output for improved slow speed loco control. Since Aristo's Train Controller intrinsically operates with Pulse Width Control (PWC), it is meant to provide for this. So I always keep the "Nudge" function in the OFF state. Thus, the MRC only serves to provide a regulated flat line DC voltage to the Aristo PWC Train controller.

Having electrically isolated the trucks from the rest of the loco, it became evident the motors had failed in of themselves.
Shown below is the truck all by itself resting on a wood block with power connected along with oscilloscope probes on each of two electrical leads.

Shown below is the Aristo-Craft Train Controller with Pulse Width Control (PWC) that I purposely limited its voltage output at about 10 volts.

The oscilloscope display below shows the Aristo PWC waveform with its voltage peak to peak value, pulse duration and rate of occurrence as applied across the motor.

The analog ammeter shown below can't follow the PWC waveform as seen on the 'scope - so it "smooths" its reading to steady amount of lesser value than what would be a peak current draw during the pulse time. Even so, the current reads an excessive 2.4 amps with the truck wheels suspended in air and slowly turning!  

If left in this condition for very long, the motor would become hot and start to smoke.
I later isolated the motor all by itself, and it made no difference in its ill performance.

As to why the motors failed, it seems the windings likely shorted, but what would have caused this to happen is undetermined at this time. The shorted power pick up leads previously described cannot cause the motors to fail.
It's possible to speculate that the motors suffered from a manufacturing quality issue, were the wrong ones installed by the factory, or not made to the proper specifications. In any event, an incoming inspection process common to many companies would be expected to catch these issues before product reaches its customers.

Shown below are some pictures depicting the rear motor block assembly and its failed motor:

With the motor separated from the gear boxes, a closer look at the parts is afforded.

As shown below, note what looks like excessive lubricant on the face of the motor with some evidence of carbon. It may be that the excessive lube managed to get inside the motor on its brushes. Whist this may cause the motor to form carbon deposits and operate poorly, I would not expect it to cause excessive current draw.

Note the hex drives meant to penetrate the gear boxes are on either end of the motor. Shown below is a view of the rear of the motor.

As can be seen in this example, there is less lubricant on the rear hex drive when compared to that of the front hex drive.

To Aristo's credit, they sent a "call tag" for the motor blocks and returned motor blocks with working motors. Aristo indicated they had to order 2000 new motors, so understandably it did take some waiting, but given a commitment to such quantities I must not be alone with failed motors. Aristo has explained that many of the motors they ordered are also to be used in motor block assemblies to be sold to customers.  

A video is available that compares a "good" and "bad" Aristo GP40 with respect to current draw (about 20 minutes).
Given the length of time it may be preferable to view it after seeing the remainder of this article.
Title: Aristo GP40 Loco Current Draw Comparison Test Using Train Engineer & Tek 2465A Scope
(Note that I misspoke near the beginning of the video as to the oscilloscope model being 6465A; the Tektronix'scope model number is 2465A.)

The video below is also about 20 minutes, title: Current Draw Tests on Aristo Supplied GP40 Replacement Motors When in the Trucks

The later part (at time 16:42) of the above video includes a description about replacing the original motor with a new motor.


The New GP40 Replacement Motors
(for Rock Island GP40, road no. 378)

When I first received Rock Island GP40, (road number 378), this unit immediately exhibited excessive current draw, though it did not suffer from a complete smoking failure like road number 392 had done as previously described.

In order to isolate which of the two motors (maybe both) is faulty, the trucks can be removed and operated independently so current measurements can be made.


Since Aristo-Craft now has GP40 dedicated replacement motors in-stock and available, Navin of customer service at Aristo sent two new replacement motors for me to install. Even if only one motor is bad, a matched set of the same production run is preferable to assure they have like kind operational characteristics when installed in the loco. This section will describe what is involved when replacing a motor.


Original & Replacement Motor Comparison

The following pictures will serve to compare measured dimensions of the original and new replacement motors:


Replacing the GP40 Motors

Given the measurements and how they impact fitment, the only issue I found to be of concern is the slight increased length of the new motor as the following pictures will illustrate for the R & R of a motor:
First, disassemble the truck / motor block.

Once the motor is extracted with enough wire lead length from the plastic cradle, unsolder the motor leads from the motor lugs and set aside.
The picture below shows how the new slightly longer motor won't fit in the cradle:

The motor will fit when the cradle is modified as shown below.

The wires from the Transient Voltage Suppressor over voltage PWA are then resoldered to the new replacement motor's lugs, and then the motor with gear boxes is to be seated into the modified cradle as illustrated in the following pictures.


GP40 Wheel Spacing & Lateral Axle Displacement Fix

Lateral axle displacement is the amount of distance the axles are allowed to move from side to side in the motor block.
By necessity the Aristo long, rigid wheel base 3 axle prime mover motor blocks require a notable amount of lateral axle displacement in order to negotiate curve tracks to avoid wheel binding on the rails. However, the 2 axle motor blocks, like used in the GP40, do not.

Thus, during operation, the GP40 motor blocks having excessive axle displacement can result in walking of the axles such that the gears are in a less than optimal mesh contact within the gear box - thereby, risking failure under load. Moreover, the displacement is pronounced enough such that coupling to cars may be problematic should the loco "walk" to one side or twist about its axis - particularly when using Kadee couplers.
Placing a 0.032 inch thick Nylon washer having a quarter inch hole over each axle stub will limit the axle movement to a reasonable amount.

Note: To avoid having to remove wheels to install a Nylon washer on an axle, the washer can be half split with a pair of dikes, allowing it to slide over the axle; however, once it's on the axle, it must be flattened out.

A video serves to demonstrate the GP40 axle displacement issue (about 5 minutes, selectable in 720P). Given the length of time it may be preferable to view it after seeing the remainder of this article:
Title: Aristo GP40 Lateral Axle Displacement Issue / Fixes & Kadee Coupler Performance

Wheel problems:

GP40s within a 100 laps around my layout

The plating wears off the loco wheel treads very rapidly resulting in excessive electrical arcing and black carbon and / or copper oxide deposits on both the rail head and wheel tread surfaces.

The below picture shows a close up example of the back deposits embedded in the area of the wheel tread's pealed-off plating!

The train cars I have do not include plastic wheels - only metal wheels, so plastic is not part of the deposits. So the combination of carbon and copper oxide - resulting from electrical arcing - along with whatever dirt, etc. constitutes debris picked up from the rail heads.
The retention of all this collected debris on the surface of the wheel tread is exacerbated by the vacated plating establishing uneven surfaces or crevasses, either from the plating wearing away or pealing off.

Progressive degradation results as the wheel surface worsens from all these factors - serving to further increase the tendency for more electrical arcing as less and less electrical contact area between wheel and rail is available; thus, resulting in more debris on both the wheel and rail head - repeating the cycle of events until the loco completely stalls for lack receiving power. I found that cleaning the wheels helps only for a short time as debris is quickly re-collected.

It got so bad that the loco operated in a jerky fashion and finally stalled as it became insulated from any power pickup from the rails!

To illustrate, I placed a machinist scale touching against the stalled loco's wheel and rail in an attempt to provide a current path ....

... and sparks resulted (shown below) as the loco jerked into operation for a split second.

Removing wheels from an Aristo "prime mover" diesel type motor block:

If you have a set of replacement wheels, the following describes an example method for properly removing the wheels.

For the GP40, the truck / motor block can be left in place as there is no need to remove it; however, the side frames must be removed. They are held in place by 3 small vertically located screws for each side frame.  The tops of screws that attach to the motor block "fingers" can be seen in the below picture.

With the loco securely placed upside down, remove the 2 small screws in the lower part of the side frame. The upper most screw only needs to be backed out so it can be left in place. The side frames can then be withdrawn away from the motor block.

WARNING! When removing the wheel/s do not attempt to pry them away from the motor block as you will certainly damage the gear box half shaft retaining mechanism.

The wheels are held in place on a tapered axle hub with a small screw and external tooth lock washer.

A wheel puller should be used to remove the wheel/s. In so doing, do not completely remove the screw that retains the wheel but back it out some so as to leave somewhat of a gap.

Though there are various small wheel pullers made or self made ones, I use a Craftsman brand automotive battery terminal puller having spring loaded jaws that just happens to be ideal in size and shape for pulling the wheels.

By opening up the jaws just a little, the puller can be slid over the upper part of wheel then downward until it is about even with its center.
(If you try to open the jaws all the way and approach the wheel head on, there is not enough room to do it this way.)

The Craftsman puller happens to have a conical like recess on the end of its rod / shank that is ideal for enveloping the head of the wheel hub's screw so when tightened down it won't slide off.

Once the wheels are removed, you can see how the axle hubs have a taper to them.

Replacement Wheels:

Not all Aristo-Craft diesel wheels are the same. The example shown below on the left is the ART-29130 replacement wheel meant for the motor blocks used in the likes of the FA1, RS3, U25B, RDC, Eggliner, etc. locos that have ball bearing axles.
The intended Aristo brand replacement wheel to use on the GP40 appears to be part number P29355-22. The GP40 wheel is shown on the right in the below picture.

If you attempt to use the ART-29130 wheel on the GP40 or any other diesel "prime mover" era gear box loco (e.g. SD 45, Dash-9, E8/E9) it will wobble (along with changed back to back spacing) as the wheel differs in its hub taper and, also, does not include the ridge on its backside hub area.

Though you can arrest the wobble by mounting the ART-29130 wheel on the newer prime mover axle as RJ Deberg has done by jamming down the hub screw against it, this is not best practice to mismatch the axles and wheel tapers and certainly not the intent of the design.

For a video demonstration by Greg Elmassian of wheel wobble, see the You Tube link below for topic:
'Difference between Aristo-Craft "prime mover" wheels and "2 axle style" wheels'

At the time of this writing, the Aristo online store shows the P29355-22 at the price of $12.00 for a single wheel for the diesel prime mover type locos.

On the other hand, the Aristo online store shows the ART-29135 at a price of $17.00 for a pair of wheels, and these are assumed to be the wheels for the diesel prime mover type locos. So the pair is the better value.

Aristo has yet to publish an "Exploded Parts Diagram" for the GP40 that would show definitive part numbers, but the diagram for the SD45 that uses the same wheel (at $10.00 each) identifies it as ART-29355 - or is it P29355-22? What adds to the confusion is the Aristo parts diagram for the Dash-9 (that also uses the same wheel) describes part number ART-29355 for the entire 3 axle motor block assembly at $95.00.

Moreover, the aristo-craft on hand in stock list shows "ART29355 MOTOR BLOCK 3 AXLE DIESEL (EA) 153.00" ($153.00) as of this writing.

So the ART-29355 must be the entire 3 axle motor block.


My experience with Aristo standing behind their product is a good one as in the example described of my failed Rock Island GP40 that was addressed with replacements motors or motor blocks.

Thus far, of 10 GP40s, two of them had failed / bad motors. (If statistics were to remain the same, that means about a 20 % likelihood of a bad loco - or about an 80 % chance of having a good loco.) That said, I think folks that may experience the same ill fortunes as I have should be taken care of by Aristo, particularly since they have an initial resource of 2000 new replacement motors to draw from if need be.  However, the outstanding issue that remains to be resolved is the wheel quality.

Since the wheels used on the Aristo GP40 two axle motor blocks are shared with Aristo's 3 axle motor block locos (SD45, Dash-9, E8/E9), one would expect them to share the same problems as previously described, too!
To wit, my SP SD45 has the plating significantly worn off some of its wheels - mostly on the rigid axle of each of its motor blocks.  In this case the center axle's wheels.

Note that subsequent production runs of SD45s have the rigid axle moved to either end of the motor block with it finally being placed at the location nearest the pilot ends of the loco.

However, since the 3 axle motor blocks have more wheels available for power pickup from the track rails, these locos seem a bit more forgiving. That said, my SP SD45 has now become intermittent in operation, too.
Though it took a much longer time for this unit to become debilitated compared to the GP40 examples, it may be that the Aristo factory wheel quality has degraded, too, since the SD45 was made in prior times.

This has become a significant dilemma to confront. Though Aristo may be able to supply replacement wheels, it seems using them would likely be no different in quality than what is on the GP40s as previously described!
Moreover, at the present time aftermarket wheel suppliers such as NWSL and Gary Raymond no longer make / choose not to make / or don't make a diesel SD45 / GP 40 loco wheel.

I know that some folks will suggest using battery power as an alternative, but I don't choose to do this for operating multiple locos pulling long heavy trains; aside which, battery power is not germane to this discussion other than to ascertain if loco wheels have their plating worn off when not being used to conduct power from the track rails.

More to the point, it is a reasonable expectation that good wheel quality be a given for any manufacture to provide to its customers - particularly since track power products are the typical standard offering. In this regard, Aristo-Craft for a short time had offered stainless steel wheels sold only with a 3 axle motor block assembly (having the correct hub taper intended for the GP40 & SD 45 axles) at a good price, but some folks discovered the shorter flanges were problematic on less than ideal layouts.

I had built to spec. stainless steel wheels custom made by Datum Precision.
The flanges on these wheels are, also, shorter at about 0.080 inch deep, but they work well on my very level suspended under house layout and my outdoor layout.


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