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How to make your Athearns run!

Posted by on Jan 30, 2015 in Miscellaneous, Tony's Tips |

“Detailed analysis & instructions for making your Atherns run.”
by Moe Mechling

I always thought that the gods of remotoring were wrong. I said before I spent a wad on motors, let me strip a loco and see what is wrong. The motor out-used .3A. That meant 1A was in the gear train. The motor draw wasn’t too bad, it could be better. I tore it down, cleaned and beveled the commutator and smoothed it up. I put a .015 KD washer on the shaft, reducing the end play to .010. I could have balanced the armature but didn’t. It drew .2A, which was within acceptable range and 1.2A in the mechanism. Now I knew it was in the mechanism, and no motor change could improve it. I worked on worm end clearance, bearing fit to the metal frame. Just checked everything for several hours. Head scratching. Then I got sore and finally I found a piece of heavy SQ plastic, took the bottom cover off, and ran the loco. I couldn’t believe my eyes. The idler gears under worm and between drivers would fly back and forth on the shaft. The casting taper and the taper inside the gear opposed each other. Assembled that way to cut down play. Each time they came to the end limit they cocked sharply and buried their teeth into the other gear roots making a bind. That’s eight times an axle revolution. I found out that the casings had different shrinkages depending on the operator’s dreaming, the bosses shoe or quitting early for a hot date. First I matched the gear taper to the stud taper. Then the two axles were put in and two KD washers and gear on the stud. The combination will vary; two .015 or one .015 and one .010, or two .010’s. The idea is to get both idlers as near to level with the drive axles in the stud side of the case. Put one washer on top of the idler stud and close the case. Too tight, put an .010 washer on top. The case held closed, the gears should roll over smoothly, with just a hint of side play. Checked with a feeler gauge it should have .004″ to .006″ clearance. I put the cases back together and it drew .25A!! Fixing that gear box assembly reduced current draw by .95A, and 1.05 over all.

The total cost was 13 washers @ about $0.26. The new Athearn mechanisms have straight posts and gear bores but still need one .010 washer and motor end play checked. The old wide body F units need worm end play checked. This needs .004-.006 end play. I would tend towards .006 for the worm.

The final problem we didn’t find until we put the receiver in the rear loco and pushed a dummy ahead with the sound unit. We hit blank sound over some switches and double crossovers. I found out that the metal interior side frames holding the wheel bearings had some kind of coating on them. Where the brass rivets crimped through they didn’t always make contact. They are also almost impossible to solder as is. I took my flexible shaft with a SQ ended carbide 3/32 moto tool burr and ground along the inside of both rivets out about 3/16″ and the joint to the motor pickup. Then I sweat the three joints using Burnley soldering paste and 2% LMP silver bearing solder (Radio Shack) the crook in the pickup is sawed off the tab, ground, and tinned. A gold-plated .1 socket for motor harness is sweat on each truck. This makes for easier maintenance and the harness is fit with .1 Micro plugs to motor and receiver. On the newer Athearn mechanisms there is a different set up. The outer pate, plastic plate, and pickup are riveted together and you must solder outside and the pickup plate inside the case.

The bottom motor retainer and spring clamp, pickup we hammer the springs back up flat, solder the plug in front of right side and put 2 pieces of plastic 4 mil. electrical tape inside the frame.

The final problem was torguing or twittering while running with the worm cover on the rear truck. Measure the space between this and frame. Subtract about .005 as ACC has thickness. It will fall in the .015-.020 range usually. Crown the pieces; cut off lengths and glue to the bolster top. This eliminates the problem and gives a three point suspension for track deviation.

To vent the body we use etched fans. Soak them in acetone to remove from the backing tape. Cut them to dia and we use a domed watch or clock glass to put the curve in. The cast fan on the body is drilled and cut away to the last ring next to flange. The fan blade ends are cleaned away with a graver leaving a flat ledge. The grill inserted and glued in place.

On the side screens we use alum fence wire often cut on the diagonal etc. The corners are drilled as shown with a #1 counter bore in a pin vice. One end is worked out; the other end freed. Trend Lines has a .010 x 40T saw blade that cuts on the pull. Saw sides free, stay in back from the edge a bit and trim with a knife and 4 cut 6″ flat hand and jewelers files. Use a vernier to get length and height even. Mark this down. Taper or bevel the inside edge. Make a dummy plug of .040 ABs plastruct. Measure the wire x 2 usually, .030, and make a plug .030 smaller than the hole. We record the hole size and loco. Set the jig on a wire rectangle. Bend the sides up with a 6″ model rule, crimp the corners with pliers and nip off the corners with scissors. Roll the rough corner with a rule and trim sides and end to the jig thickness and remove the screen pan. Push the pan in from the shell from inside use a rule to get outside flush. Check inside that no wire sticks out to short the receiver and ACC in place. Blot excess with squares of “Bounty” kitchen towel. We do this all before super detailing the model, after learning the hard way. Had a whole box of spare parts.

About 90% of Athearn frames are bent from casting and shrinkage. It’s easy to spot. Put a finger on both ends of the shell and if it rocks up and down, it is bent. When you strip the chassis out to work on the mechanism, put a wood block under the end and tap with a hammer to straighten each end. Let it sit on the tank. Check with a straight edge.

We saw the coupler tabs off the frame and build up the shell inside for the coupler pads. Using #5 KD’s almost exclusively. Especially if a snow plow is on the front. The rear pad is too low for #5 and too high for #7’s, about .020 off.

“Toot toot”
“Mocn3” Mechling
NMRA 2711