USA Trains F3 A/B Unit Experiences & mounting Kadee Centerset Couplers

USA Trains F3 A/B Unit Experiences & Mounting Kadee Centerset Couplers
Ted Doskaris
Initial Release, A
April 18, 2019

May 4, 2019, Rev GE-B  Added video of 61 car train



Shown below is a USA Trains 1/29 scale EMD F3 A and B unit set having been fitted with body mounted Kadee "G" scale centerset AAR "E" type knuckle couplers in 3-D printed coupler boxes. The A unit nose now includes an operational Kadee centerset coupler in place of the factory dummy coupler.

Note that the locos' coupling distances are more prototypical being closer together than factory, and they are intended for operation on 8 foot diameter or greater track curves. (For layout operation on "S" bends having diverging opposite directions, a straight track section about the length of the longest car should be used there between.)


This vignette (article) is fairly large with 80+ illustrations along with descriptions that include many issues aside from mounting couplers. Directly accessible (clickable) contents are listed below.


Coupling Distances
Couplers & 3-D Components
Diaphragm Preparation
CamPac Component Installation
Non Coupler Issues:
Dismantling Loco
Cab Removal
F3 A Unit Nose Door
Chassis & Fastener Issues
The "Wet Noodle" chassis
Stiffener Plates
Optional Current In Rush Resistors
Wheels, Axles & Traction Tires
Motor Block Axle Replacement

Miscellaneous Items:
A Unit Nose Door
A Unit Windshield & Windows in General
A Unit Windshield Wipers
Side Screens
End Cut Lever & Bumper
Rear Light
End / Rear Hoses
Roof Fans
Exhaust Stacks

CamPac Stress Test Video

Obtaining CamPac Products





At this writing, factory new F3s seem to be in short supply, at least until USA Trains can produce more that is supposedly in the offing along with what has been purported to be a new evolutionary F7 offering!

Consequently, the F3 A and B unit, followed by another A unit to be described were acquired used but in very good condition; however, cleaning and some repairs were needed along with restoring a few missing parts, making some improvements, and of course, some minor modifications to accept 3-D printed coupler boxes that I (Ted Doskaris) developed in concert with Colin Camarillo, who has the 3-D printer and software expertise to implement them.

Borne from working on the used units, there are a number of ancillary issues & fixes also to be described.


USA Trains markets and packages the B unit in a set with the A unit - apparently the only way to obtain a new B unit.

The A unit can be obtained individually to complete AA set or an ABA set

First to be described pertains to the coupler boxes.

Shown below is the 3 unit F3 ABA set together fitted with body mounted Kadee centerset knuckle couplers in the 3-D printed coupler boxes.

The A units coupled nose to nose, shown below, are also operationally functional.

Operational capability with all 3 units coupled together is down to 8 foot diameter curve track.




Coupling Distances

Illustrated below is a coupling distance comparison - factory vs. locos equipped with CamPacTM 3-D printed coupler boxes fitted with centerset couplers from the Kadee 907 kit.

With the shorter coupling distance, a slight air gap with diaphragms reduced to 3 flutes was chosen for operation when locos are going in and out of tight curves.

Though it would seem with the excessively long factory coupling distances and 6 flute diaphragms meant to touch would seem to work, I found evidence of cracking damage on a used F3 that likely resulted from binding during operation in & out of curves, particularly in the presence of outdoor UV light rays that do not help for longevity.

Shown below is a modified and repaired diaphragm (USA Trains did not have a new replacement in stock.)

Comparative coupling distance measurements are shown in the following illustrations:

The original factory distances are shown below.

When evaluating the F3 for the closer fit distances, I took into account other locos and rolling stock, including the Aristo-Craft E8/9 that has a factory 3 flute diaphragm and was refitted with Datum Precision metal coupler boxes with Kadee centerset couplers for closer coupling distances, too.

When determining coupler alignment positioning to the standard (Kadee 980 gauge), the height of the F3 is examined to see if should be corrected if too far off. The factory height of the F3 is very close to the prototype in spite of its tiny, under scaled, wheels as can be seen below.


Couplers & 3-D Components

The CamPac 3-D printed coupler boxes and mounting pedestals are the same but configured differently for installation on the F3 A & B units as illustrated below. Note the A unit pilot end is different when compared to the end of the loco or B unit.

As shown in the illustration above, the box can be premounted on the pedestal, except at the pilot end of the A unit because it may be difficult due to its confined opening where the pedestal is best mounted on the chassis first.

The boxes are optimized to use the coupler from the late version Kadee 907 kit, not the old predecessor 789 kit - with differences shown in the illustration below.

If using the introductory version 907 kit, the coupler shank hole is to be slightly enlarged to somewhat emulate the late version so it won't bind on the box pivot post. This could be done to the old coupler from the 789 kit with its even smaller shank hole, too.

Note: When assembling the coupler, springs and lid on the CamPac BoxTM, two screws must be used to hold the lid in place - required for operational stress. Should the coupler not freely swing side to side, the screws can be slightly backed out one at a time, and / or the coupler shank surfaces may need to be burnished.

Diaphragm Preparation

To facilitate closer coupling distances, the diaphragm on the end of the A unit and both ends of the B unit must be shortened. Alternatively, the diaphragm can be removed and discarded - a practice done by many prototype railroads.
The diaphragm can be removed without taking off the car body shell, but it can't be readily reinstalled that way.
Illustrated below is a method for removing the diaphragm without taking off the body shell.

To remove the diaphragm with the body shell off is illustrated below.
Note that the end door is to be removed. It's held in place by wedge action that fits into corresponding slots in the body shell end bulkhead. (Other body shell side doors employ a like kind design.)

To install the diaphragm would be in reverse order to that shown above.

To install the diaphragm, it's a given to take off the body shell to gain access to its interior - described in "Dismantling Loco".

When choosing to keep the diaphragm, it is to be modified as illustrated below.

Advisory: When installing the diaphragm on the body shell, first seat it in the door opening surrounds, and then install the door at its hinge side first whilst holding in the diaphragm on that side to keep it from being pushed out - illustrated below.

Advisory: Both the door hinge side and opposite side small wedge may need a little more than finger force to install them - in which case a light tap with plastic mallet buffered with small wood stick may be helpful.

CamPac Component Installation

A guide has been published in PDF format, available on Colin Camarillo's Web site, that describes what and how is to be done to install front and rear CamPac coupler boxes and their pedestals, title:
"Installation Guide, USA Trains F3 & CamPac Components"

To Summarize:

Before installing the CamPac box with centerset coupler on the F3 A unit, its pilot needs to be slightly modified (notch to be cutout below bumper).
Illustrated below is a before and after comparison with coupler installed and "dressed" cut levers.

Without coupler, the cutout (0.820 inch wide notch) is below the bumper as illustrated:

Illustrated below is detail to be cognizant of when installing CamPac components.


Illustrated below are installed CamPac components.


The following includes a little more information that may be helpful to know whether or not employing CamPac components:

More about F3 A unit Front Pilot:

If only desiring to separate the body shell from the chassis, the pilot with coupler can be left in place on the chassis.
However, because the pilot requires slight modification when mounting the CamPac BoxTM with centerset coupler, it's best to remove the pilot to make it easier to work on. The factory coupler & mounting pedestal (or other aftermarket parts) must be removed, too.

The USA Trains factory default coupler mounted on the front of the A unit is an ornamental "dummy" coupler that can be removed with or without removing the pilot from the chassis.

The difficulty is that the dummy coupler is fastened with a screw from the underside of its mounting pedestal, so it can't be taken off by itself, thus, the pilot would be prevented from being removed. This is further complicated due to the confinement of the pilot's knockout plug - illustrated below.


The solution is to first unfasten the pedestal from the chassis so that:

(A) The pilot could be collectively removed from the chassis along with the coupler & pedestal

OR when the pilot is left in place, push the pedestal with its coupler forward and manipulate it so that:

(B) The knockout plug is freed from the pilot along with the coupler & pedestal - sometimes that may not be easy to do!

OR when:

(C) The cut lever hooks become disconnected from the oblong on the coupler's knuckle. In this case the coupler with pedestal can be turned 90 degrees and wiggled up & down through the confines of the knock out plug & pilot whilst being withdraw in the direction toward the fuel tank.

See illustrations below.


F3 A End & B unit Coupler:

Removing the factory coupler and its mounting pedestal (or other aftermarket parts) is needed to accommodate CamPac components or may be needed for other reasons.

The USA Trains factory default coupler mounted on the end of the A unit, and on both ends of the B unit, is the hook & loop coupler which can be removed with its pedestal from the chassis.


Cut Levers

Pilot Cut Levers:


After the modified pilot and CamPac components are installed on the F3A, the cut levers can be "dressed" as shown in the example illustration below.

The dressed cut levers bear a reasonably close resemblance to the example prototype shown below.


Units' End Cut Lever & Centerset Coupler:
The F3 A end and both ends of the F3 B typically will need to have the cut lever "tweaked" to allow the once mounted CamPac BoxTM centerset coupler to freely swing side to side without interference and for the coupler to best align with the Kadee 980 gauge - described in the illustration below.


Non Coupler Issues:

Dismantling Loco

Screwdriver Type Needed
To separate the body shell from the chassis, a long, narrow shaft, Phillips #1 screwdriver is needed to get around various parts, some at slight angles, and yet be able to engage the Phillips head screws that fasten the body shell because the screws are within narrow recessed pockets that extend below the chassis surface.

An example Steelman brand chrome vanadium magnetic screwdriver set at reasonable cost purchased via is illustrated below.

Truck Sideframes Stirrups
To get to the chassis fastener on the A unit's nose (or to make it easier to get to some other fasteners) one of the truck's sideframes can be removed and set aside with its electrical wire still attached. To gain access to two of the screws that retrain it, the hanger stirrup can be removed and later reinstalled - Illustrated below.


Chassis Fastener Locations
The chassis to body shell attachment locations are illustrated below along with method to lift out the chassis. Note the pilot and couplers are shown removed, but could be left in place. Ladders can, also, be left in place.

Caution: When lifting out the chassis, it's very much a "wet noodle" - excessively flexes , so it's helpful to lift at the end truck, too, so not to risk breakage. This can be mitigated by adding stiffeners - described later.

Electrical slide switches with embossed functional identifiers are located on the chassis between the front truck and fuel tank at the same place for both A & B units.


Advisory: To avoid having to remove the unit's end brake hoses, its protruding mounting prongs (pegs) can be cut as illustrated below.

The separated F3 A & B unit body shells from respective chassis are shown below - exposing these example early units' internal circuit boards.



Cab Removal

Illustrated below is how the cab assembly with engineer and control stand is withdrawn from the body shell. Screws are not used to retain the cab.


F3 A Unit Nose Door

The small door on the front of the A unit appears to be designed to be opened, however, the mechanism that allows it to be like a plug type door is not too conducive for use.
Moreover, the bottom of the door could noticeably protrude out. It seems the factory is aware of this in that masking tape is sometime applied across its interior side to keep its outside flush with the loco's nose. Over time the tape comes loose. If using tape, black electrical tape is a better choice, but cutting a small piece of rubber can be used as illustrated below.



Ladders do not have to be removed when separating the chassis from the body shell, however, they may become dislodged during handling. Their removal / installation is illustrated below.



Chassis & Fastener Issues

Factory screws with self tapping tips are threaded into the body shell posts that would not have been prethreaded when assembled by the factory. Substitute screws can be obtained trough if screws are lost or to replace factory screws with more desirable self threading type screws with pointed tips - illustrated below.

Illustrated below is a measured comparison of the factory and Uxcell replacement screws.


Because the chassis is very flexible (likened to a wet noodle) it could assume a warped attitude if not properly installed. This affects how body mount centerset couplers align as intended with the Kadee 980 coupler height gauge.

This is a subtle condition, so it's important to assure all body shell smaller diameter posts seat into the chassis's recessed posts, and be aware of a potential problem when using screws to refasten the body shell to the chassis.
Particularly, the holes that should be screw clearance holes in the chassis recesses are too small such that when attempting to thread screws into the mating body shell posts may cause the two to not fully seat, or when tightening to seat the posts together could risk stripping out the body shell - illustration below.

Note: It's preferable to use the Uxcell (or equivalent) pointed tip screw fasteners in prethreaded holes to help avoid cross re-threading.

The "Wet Noodle" chassis

Chassis flex is very noticeably pronounced to the point of being disconcerting when removing it to the extent if it could break! The weakest point is in the center where the large center hole compounded by where factory notches are on the side sills.



Stiffener Plates

An example remedy for the flexible chassis is to use steel stiffener plates that also adds about one pound of weight that will be described. An upper and lower plate serves to clamp the chassis's mid section, thereby, stiffening it at its weakest area.

Note: If desiring to use a speaker in the fuel tank, an alternative to the stiffener plates is to use Dave Stubbs' 3-D printed enclosure which will serve to stiffen the chassis, although the factory circuit boards are done away with since Digital Command Control (DCC) circuitry is employed in this example. This is described by Greg E., subject title:
"F3 DCC install" (Scroll down to "Speaker Installation w/ 3d printed enclosures" Using Dave Stubbs' speaker enclosures".)


The stiffener plates are cut from 3 foot long steel flat bar that was obtained from Home Depot.

The upper plate with dimensions is illustrated below.

Note: It's preferable to drill & tap the center hole as shown above to accommodate an extraction loop that could be removed then reinstalled for when separating the chassis from the body shell - described later.

The lower plate that is to reside in fuel tank side of the chassis with dimensions is illustrated below.

The upper plate must be insulated at either end to avoid electrical short circuiting circuit boards that it will be placed under. Shown below is using thin ABS plastic obtained for TAP Plastics.

The ABS material shown above may no longer be available, but a thin gauge polycarbonate substitute obtained from TAP Plastics can be used as shown below.

Once the glue dries, use the metal as a template to drill the holes through the plastic.

Example plates weight is shown below.


Extractor Strap

With plates installed on the loco, the large hole in the chassis center is covered so it can't be used to put a finger through to help lift out the chassis from the body shell. To remedy this, an extractor strap can be made from scrap flexible plastic that may be found in the TAP Plastic store discount bin - example shown below. (Formed into a loop allows one to put a finger through it)

The strap is placed over the lower stiffener plate hole, and the #6-32 screw would go through it, and thread into the upper stiffener plate then tightened serving to hold the strap and both plates in a clamping fashion on the chassis.

Optional Current In Rush Resistors - Applicable to Track Power

Adding a 1 ohm resistor in series with each motor is mostly applicable for track power users to mitigate wheel pitting when operating with pulse width modulation (PWM/PWC). George Schreyer investigated this issue in great detail that seems to be more at issue with type of electric motors USA Trains uses.  See George's Web site section on Wheel Pitting.

The trade-off of adding resistors is to slightly slow the loco's speed. Since the F3 seems to run a bit fast for my tastes, I found this not to be objectionable - even desirable - since the F3 can be a better speed matched when "MUing" to a USA Trains SD 40 or an Aristo-Craft FA/B1, RS3 and even a GP 40.

Resistors used were sourced from China at reasonable cost via - shown below

The two 1 ohm, 10 watt, resistors are installed on the upper stiffener plate.

As shown below, the resistors are located to be clear of the plate's center hole. The holes in the resistor body ears can be used as a template to mark the plate for drilling & tapping #2-56 mounting holes.


In the example shown below, the wiring was done with matching connectors so the motors can just be unplugged from their factory receptacles, and then the resistors plugged in between.
(Only one of the two wire leads for each motor will have a resistor mate to its connector; the other lead is connected straight through.)

Installed end to end at connectors is about 9 inches apart

Stiffener Plates Installation

A stiffener plate is installed on each side of the chassis. The longer plate with insulators on each end is to be placed under the circuit boards over their mounting posts on the interior side of the chassis. Hence, three circuit boards with their fasteners must be temporally removed - illustrated below

If employing current inrush resistors, they will be clear of the remounted circuit boards


If using a sound speaker or other electronics in the fuel tank area, small hole/s for connecting wires can be drilled in the area of the stiffener plates as illustrated below.


Once the upper plate is installed with the circuit boards refastened that will keep it from moving around, it will become evident from seeing the illustration below why it's preferable the upper plate center hole is made with threading for a #6-32 screw rather than relying on a screw with a nut.

Note: If using a speaker in the fuel tank, the #6-32 screw can be installed (sans the extractor strap) to clamp the plates together between the chassis knowing the upper stiffener plate won't move around. If access to the interior is needed sometime in the future, the strap could be reinstalled to facilitate separating the chassis from the body shell.

Loco Weight

Stiffener plates installed in the loco will add about 1 pound.

The resulting weight of a completely assembled F3 A unit is shown below.


The resulting weight of a completely assembled F3 B unit is shown below.



Wheels, Axles & Traction Tires

Wheels with rubber treads are known as having traction tires.

Many USA Trains locos utilize wheels with traction tires on one axle in each truck, including the F3. Traction tires afford notably more grip benefiting a light weight loco. However, when the loco is powered and possibly stalled from an obstruction on a layout, the motors are in jeopardy from being damaged. Also, when "MUing" the F3 with other locos that have a lower speed characteristic, the motors will tend to draw more current than desired. Moreover, for track power users, locos employing wheels with traction tires will forego power pickup points from the railheads from the wheels on these axles. Another issue with traction tires is their affinity to pick up dirt or/and the rubber deteriorates so that a sludge is deposited on the rail heads - electrically insulating the track. To mitigate this, power pickup slider shoes are included on USA Trains locos.

As an alternative, all metal wheels will be more forgiving, even when adding a reasonable amount of weight to a loco to improve traction because they will more readily slip or spin when the loco is obstructed or overly loaded. Also, two additional pairs of power pickup points per axle will be afforded.
Depending on layout track work, some folks may have trouble with the slide shoes having mechanical interference and resorted to eliminate them, so replacing axles having wheels with traction tires with metal wheels may be desired depending on specific conditions or needs.
In the event a train needs more capability to pull it, do what the prototype railroads do and add another loco/s.

Aside from being under scale, another issue with USA Trains loco wheels is their inherent tendency for the plastic axle to split at one or both ends. This malady has been prevalent for many years and persists to this day!  A failed F3 axle is illustrated below.


Whilst USA Trains typically has replacement axles available for purchase (and one wonders how long it will take to fail!), a split axle is reparable in most cases. A fix using metal tubing has been known and used by many folks for a long time. Namely, repair collars (aka, sleeves) can be cut from a brass tube and slipped over a split axle. As a pre emptive measure, some folks will put the collars on a newly purchased axle to prevent it from splitting.

An example K&S Precision Metals 10 mm x 0.45 mm wall thickness brass tube, #9828, that I had obtained from ACE Hardware is used for the repair - Illustrated below.

Note: Repair collars made from K&S Precision Metals #9828 brass tubing having a 0.45 mm wall thickness when put on the plastic axle will fit in the motor block - whereas, a thicker wall may not.

When using a tubing cutter, the collar's end residual ridge must be cleaned up and tapered to facilitated installation. An alternative method to use in place of a file from that previously shown is illustrated below.


Wheel Installation on Plastic Axle

Two methods will be described. Both methods are similar in execution:

Method 1 without needing specialized or dedicated tools, and
Method 2 using Eric Reuter's excellent 3-D printed jigs. These can be printed using Eric's downloaded files if you have access to a suitable 3-D printer, or you can purchased the printed jigs from Eric.

The following illustrations show available jigs:

The triangular jigs are used for pulling wheels from the plastic gear. User supplied #10 screws and nuts will be needed when using these.

The jig below will be used for installing wheels on the two axle loco plastic gear axles.

Method 1, No special tools:
Without having specialized or dedicated tools, a technique for installing wheels on the repaired axle will be shown.

First, start by minimally inserting the wheels' stubs in the plastic gear's axle - illustrated below.

Then press on the wheels - illustrated below using a drill press.
(A vise having a 3 & 1/2 inch to 4 inch or greater jaw opening could be used, too.)



Method 2, Using Eric Reuter's Jigs:
Eric's jigs are excellent for making convenient wheel installation, not only for pressing them on, but the wheels are correctly gauged in the process, too.
A technique using Eric's 3-D printed Jigs dedicated for installing wheels on the repaired gear axle will be shown.

Whether or not choosing to prep the wheels as shown above, press the wheels on with the gear in the jig - illustrated below using a drill press. (In place of a press of some kind, a vise having a 3 & 1/2 inch to 4 inch or greater jaw opening could be used, but jig disks with hole for the axle tip, or substitute, will be needed.)




Motor Block Axle Replacement

An example technique with respect to axle replacement in a motor block can be deduced by examining the illustration below.



Miscellaneous Items:


  • Some of the items that follow may have been previously described and shown but are again presented for convenience.
  • In some cases, the body shell will need to be removed to gain access to the interior.

A Unit Nose Door
The bottom of the door could protrude out. The factory often uses masking tape applied across its interior side to keep the door's outside flush with the loco's nose. If the tape has deteriorated or no tape was used, black electrical tape can be used. Alternatively, cutting a small piece of rubber can be used as illustrated below.


A Unit Windshield & Windows in General
Windows often come loose when handling or can fall within the loco over time. Illustrated below is an example method for fixing the windshield. The same method can be used for port hole windows in both A and B units.



A Unit Windshield Wipers
Windshield wipers are very small and may be broken when handling. Installation of a replacement wiper is Illustrated


Side Screens
Side screens are prone to distortion when the loco is handled with fingers in that area or may bulge out, sometime owing to temperature changes. An example bulged side screen remedy is illustrated below.


End Cut Lever & Bumper
The A unit rear or B unit end cut lever is factory fastened to the chassis with plastic eyelets that are "mushroomed" over with heat on the body shell. If too thick, they may present some restriction if removing the chassis. When using CamPac BoxesTM fitted with centerset Kadee couplers, the cut lever typically must be bent to not restrict swinging of the coupler. Also, the long rectangular bumper tends to come loose and can be glued in place. See below illustration.



Rear Light
Both A & B units employ a rear back up light that is enable by a slide switch grouped with other switches on the underside of the chassis. The light is retained on the interior bulkhead with factory masking tape that can lose its adhesion over time, and then the light can fall within the body shell. The tape also serves to retain a piece of reflector foil. Illustrated below is a repair remedy.



End / Rear Hoses
There are two groups of 4 hoses that may become loose or need to have their mounting prong (pegs) trimmed off so not to be a restriction when removing the chassis - illustrated below



Roof Fans
Each of the 4 roof fans is a module assembly. The fan assembly can come apart and fall within the loco. Illustrated below is an example repair method.


Exhaust Stacks
The loco comes with 2 metal and 2 plastic oval shaped exhaust stacks from the factory. The metal ones are preferable when using the smoke units owing to heat and the fluid used. The exhaust stacks are slightly tapered from top to bottom and may fit into their respective roof recesses too loose or not fit being too tight. Illustrated below is a method for attaching loose plastic exhaust stacks so not to fall out when handling the loco.


CamPac Stress Test Video

See video of a long 35 car train with body mounted Kadee centerset couplers being pulled by a USA Trains F3 ABA set.  The 3 locos are fitted with CamPac BoxesTM having Kadee centerset couplers.

The more modern and mostly 50 foot type longer cars on this train may not be prototypically correct for the era of the F3 locos, but their collective car weight of about 125 pounds resulted in a draw bar pull approaching 5 pounds is to be appreciated.



See video of a longer 61 car train with body mounted Kadee centerset couplers being pulled by USA Trains F3 ABA set (but having to add a GP7/9). The 4 locos are fitted with CamPac BoxesTM having Kadee centerset couplers.

This train with mostly 40 foot type cars is more prototypically appropriate for the era of the F3 locos. The collective car weight on this train is about 170 pounds.




Obtaining CamPac Products

CamPac 3-D printed products, including F3 mounting pedestals and coupler boxes designed to accept Kadee centerset couplers, are available by contacting Colin Camarillo via his Web site.






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