Athearn blue box locos need

Athearn blue box locos need the motor isolated from the frame first.  You need to remove it and cover the frame it sits in with electrical tape.

Current draw in many is ok but really old Athearn maybe not.    I think the idea is you measure the stall current and it is within the rated max current of the decoder it's ok 

Digitrax used to make, maybe still does, a decoder for Athearn blue box locos.

Ernst Gearing!

Back when we wanted the engines to crawl because the motors would cog too much.  Most Athearns with the GOLD sided motor will work just fine with most decoders today.  As for the gearing, I afraid that in my experience they will have to be brought back to stock gears to reduce the friction on the drives.  The few I had with Ernst gears just would not run well with DCC.  To much drag on the drive train was the culprit.  I returned them all to stock gears, tuned up the drives and re-installed the decoders.  I had much better luck this time with slow speed control as the drives were free rolling. ( The Ernst gears did not allow my trucks to free roll).  Now as for installing DCC in the older Athearns, there is a vast amount of videos on the internet on how to do it.  Use the search function on this site and you will get plenty of information.

  https://forum.mrhmag.com/post/dcc-conversion-of-an-old-athearn-locomotive-12209457

https://forum.mrhmag.com/post/athearn-blue-box-and-dcc-12188183

Here are a couple to get you started!

The blue box locomotives and the Protos are worth the time.

Especially if you like to tinker a little.

This  is a good article and outline of motor isolation and truck wiring.

http://www.mcor-nmra.org/Publications/Articles/Athearn_TuneUp.php?fbclid=IwAR1y6_vRCNabtbX8Yp2Ol_E1OntPIdXQjYUGf6n7G8VXGxNRSmzAcf-b_oY
 

The way I happen to have developed is to either use Kapton tape to tie a Decoder Buddy to the top of the electric motor.  Then I can add a 21-pin decoder from any manufacturer, sound or no sound, stay alive or no stay alive, a lot of lights or maybe a headlight and an back light and learn what works for me.  The Decoder Buddy is a very versatile decoder holder that allows you to change decoders very easily.  It also organizes the installation of a decoder into a neater package for a better chance of a successful DCC installation.

This one is waiting for a decoder and then to the layout.

If you would like to watch a very fine installer in action Larry Linger, Solo Contracting on YouTube is the guy!

Here’s one to get you thinking about the proposition.

Enjoy!

  "As for the gearing, I

I had the same experience with Ernst gearing. The extra friction canceled out the low speed gearing advantage so the stock gearing ended up running better at all speeds.....DaveB

If you can change gearing...

...then you can easily change out the decoder. I always like to direct people to  TCS' website, because even if you don't use their decoders, they still have very good advice for all sorts of decoder installations in locos.

Just to restate what was said

Just to restate what was said above.

I'm assuming we are NOT referring to the rubberband drives.

If these engines are from the 1980s or newer with the gold flat can motor and brass flywheels, then they will be 100% fine to convert to DCC unless the motor itself is damaged.

If it's the Steel flat can, or the round motor that forced the over wide shells, then it's a definite maybe and you need to test the stall current. Personally, I'd swap out motors for anything older than a gold flat can. 

I can't speak to the gearing, but it sounds like others know the deal and have given the needed advice.

I'm assuming we are NOT

I'm now 62 and while I have heard of rubberband drives, I've never seen them.  They must be really old!

Yeah, the gold motor blue box should be fine with decoders.  I think it's the older motors that may pull more amps and need to be checked.  Even the first 2 runs of the LL Proto 2000 Alco PA's pulled high amps so it isn't just old Athearns.

Adding sound

If you have any interest in adding sound to a Blue Box, check out this article from MRH:

https://forum.mrhmag.com/magazine-feedback-was-ezines-891776

For just adding DCC and LED's, you might find this article useful:

https://forum.mrhmag.com/magazine-feedback-was-ezines-891776

I'm now 62 and while I have

I just turned 46 and I see them all time time at Shows and in Donations to the club. I believe Athearn stopped using them in the 70s. 

I have a rubberband drive RDC. My plan eventually is to convert it somehow to a standard drive.

Rubber band drives

My first HO engine was this  Athearn GP7 with rubber band drive.That was 1957 and these models were pretty new at the time. They retailed for $7.95 IIRC. Mine has been converted to a later gear drive.If I ever build another HO scale layout I'll add DCC and sound to it.....DaveB  

Old athearn s to DCC

C’mon - no remembers the rubber band Hustlers that could hit 400+ scale mph on a straightaway? As a kid my rubber band F7 was my best engine for going over my grade made from stacked books. Geared engines were too heavy and pushed the fiber tie flex track down. Would NOT convert them to dcc as replacing would be cheaper and way better!

isolate the motor, add DCC,

isolate the motor, add DCC, done

To isolate the motor from the frame do the following:

After disassembling the drive shaft system from the motor/flywheel assembly, remove the motor from the frame stripping it down to the 2 brass clips holding the motor together.  Carefully holding the motor together swap the top and bottom brass clip.  With the brass clips swapped, you can reinstall the motor in the motor mounts and notice that the bottom clip no longer makes any electrical connection to the frame.  The motor is now isolated.  If the 2 "fingers" in the top clip now interfere with the installation of the decoder, they can be mashed back into the brass clip with pliers, or cut off with flush cutting nippers.  There is no need for any insulating tape on the bottom of the motor.

The rubber band drive

We’re call Hi F or something like that.  Over that last fifteen years, I fixed up dozens of these engines.  I also sold bands separately and they sold consistently.  I stopped because I have focused on more modern engine repair.  I’m sure there are people who still run them.  The bands have a limited life, so your always needing to change a band or two.  
the motors fit third and the later round jet motor have stall currents approaching 3 amps.  Early in DCC days there were decoders that would handle this.  However, you need to consider this because these motors pull around 1 amp with a nominal train load.  This plays havoc with a DCC current budget that is around 5 amps per district.  The older gold rectangular Athearn motors are much more workable.  Their stall currents are around 1.5 amps and the nominal train load current draw is around 0.6 amps.  The later high performance & Genesis motors run about 2/3 of these values for reference and those come regularly are used with DCC engines.  
As others have said, the Ernest gears were a solution for the round black jet motor mentioned above that had a starting speed around 25 SMPH and a top speed of 200.  They also had the power to deal with the extra gear load.  The later motors will not tolerate that much internal shaft drag.  I have measured an engine only current level of 0.8 amps with these gears.  With a nominal train load the motor will be operating uncomfortably close to the stall(max) level.  Motor will be generating a lot of heat and will likely not last long.  Lots of reasons to go back to the conventional gearing.  The DCC module will give you better speed control without the power loss.

As has been indicated, lots of how to posts on line & on you tube.  
have fun.

I'm 77 and I remember Rubber Band Drives

Jim, your just a kid. 

My first HO locomotive in the mid 1950's was a Lionel knockoff of the Athearn Hustler powered by rubber bands. The shaft from the motor had a plastic sleeve for the rubber band.   I later had Athearn F units with the slightly rough plastic axel drums for rubber band on the trucks. How these engines picked up rail power, I can't remember. They went like bats out of hell with little speed control. 

Now if you remember the early X2F coupler....

Rubber band drives and the discovery of girls put me off model railroading for a while. 

Modifying Athearn "Hi-F" GP9

I have an Athearn GP9 with the rubber band drive, with the older motor.  It worked okay, as long as the rubber bands didn't travel off the end of the drive shaft.

Just for the fun of the challenge, I am attempting a major refurbishment, including a new motor (from Micro-Mark), new shafts, and most importantly, redoing the truck pickups.  The wheels were isolated from each other, making contact with the truck side frames.  The side frames were isolated from each other, with one side having a wire to the motor, and the other side making contact through the truck pivot and the frame.  I am adding a second wire for the other side.  The leads for the new motors are isolated from the frame.

And if it works, I just might add DCC, a low end unit.  I don't care all that much about exact engine sounds, for my purposes, a diesel is a diesel.    Bells and horn are adequate for me.

  "Just for the fun of the

I think the key to improvement in performance would be to add a secondary reduction of about 3:1 to slow down the speed range. Some kind of jackshaft shouldn't be too difficult to construct....DaveB

Old Athearn...

Old Athearn ran many a' mile on my layouts of yore.

My first Athearn was a rubber band drive Santa Fe freight F7 purchased in the mid-60s. Not impressed. First geared Athearn was their SW in Santa Fe "Bookends". Loved that little switcher. From there on out I was an Athearn customer that covered most iterations of their drives. The move to flywheels was a BIG DEAL. I had some older Athearn w/flywheels that ran surprisingly good.

Once Kato hit the market (late 80s), and Front Range came out with their scale hood width GP7/9 (late 80s/early 90s?), my Athearn purchases dwindled. Stewart/Kato F's did them in. I never purchased another Athearn locomotive product until late last year when I purchased a Genesis Frisco GP7 w/TS2 off a friend. It's a fine engine that runs/sounds superb.

Good memories concerning Athearn's old stuff... but I don't wax nostalgic enough about them to warrant obtaining examples.

DaveB: Your Zebra Athearn GP looks pretty good!

Andre

Stewart/Kato F-units are

Stewart/Kato F-units are still my goto. Excellent generic detail, incredible drivetrain and easy to DCC.

Stewart/Kato F-units are

I agree.  Even though my Stewart F's don't have as much detail as my Genesis, they are solid and super smooth operating. And why somewhat generic, Stewart did offer 4 phases of F3's, 2 phases of F7's and one phase of F9.