For those of you who would like to reduce the speed of your diesels made by Mehano, and then sold by AHM, IHC, Model Power and some others to a more realistic speed, NOW YOU CAN!![:D]
These steps show how to reduce the speed using Kato worm gears.[:D]
UPDATE: While I was working on my Atlas HO 8-40B today, I found that the size of the Atlas worms is identicle to the Kato worms. The part number for the Atlas worm is 850318[:D]
Step 1: Remove the truck retainer on the top of the truck using a small flat-blade screwdriver. Then remove the truck. (Sorry about the fuzzyness of the first couple pics. They’ll get clearer later)
Step 2: Remove the truck sideframes/wheel and gear retainer from the truck by un-snapping the front latch with a flat-blade screwdriver, pulling the front of the piece down, and then sliding it off the coupler retainer.
Step 3: Unlatch the gear retainer on the side of the truck by un-snapping two latches on the other side of the truck, and then sliding the retainer off. Once the retainer is off, remove the white nylon worm gear from the truck.
Step 4: Remove the bearings, washers and shaft socket from the Mehano worm. Put the parts onto the Kato worm. Be sure to put the rear bearing on so the square end is on the
Hey another Idea to use. Nice post on sharing ideas Darth SF. Ive been doing the Ahm/Riva loco’s for years, remotoring is big improvement on the steam. Thanks for the info.
dingoix, they run between 150 and 170 scale MPH with the factory worm.
Kato doesn’t list the worms seperately on their website for some reason, so you’ll probably have to call or e-mail them to order some. One thing that’s even weirder is that they do sell the bearings for the worms on their website.[%-)]
Great piece!! You should submit as an article to one of the mr mags.
A bit more technical comment:
The Mehano worms are double lead, the Kato worms are single lead…
The is a replacement of the worm, not the worm gear.
The original gear ratio in the Mehano drives is 8.5:1 (2:17 double lead worm with 17 tooth worm gear). With the Kato worm, it becomes 17:1.
This will also work on some Bachmann GP9 models, some Mantua F7 and GP20 models.
Another low cost method of reducing the speed of these locomotives is to use the Mabuchi motor Mantua used in thier last F7 and GP20 models. It is a low speed motor with a skewed slot rotor. Combining the Mantua Mabuchi motor and the Kato worm will provide scale speeds in the 40 to 50 mph range at 12V. This is probably the same motor as "the silver open motors " that DSF referred to above.
I do know that the spiral gears are called “worms”, but there are some people and manufacturers (like Athearn) that call them “worm gears”, so that’s why I said that.
I believe the motors in the Mantua diesels are can motors, like the ones IHC uses. These same low RPM motors were also used in Walthers diesels. The silver motor I was talking about has a large round hole on each side of the silver part (black with AHM diesels), an exposed commutator and a 3-pole un-skewed armature, which gives them terrible low speed control. They also have the name “Mehanotehnica” printed on them, which is Mehano’s original name.[^]
Thanks for that calculator![:D][:D][:D] Now I can actually figure out how fast something’s going![:D]
With the Kato worm, they go 68.44 scale MPH. If everything is adjusted right, the lowest speed should be around 3 scale MPH. (I can’t test the low speed right now. I had to take the Kato worms out because my SD80 wanted them back [:D])
With the Mehano worm, the speed is actually 136.89 scale MPH, which is still pretty darn fast for a freight diesel.[:0]
Looked at the exploded diagram. It only shows the worm as being with the bearings, joint and worm/truck retainer. The part number for that whole set is 961500 and costs $4, but there may be a way to get the worms alone. Maybe you could buy two sets to repower one engine and sell the bearings, joint and retainer on eBay, or keep them as spare parts.[:D]
I’m sorry, but that’s all the info I can give you.
Just a note that there is a possible drawback. The double lead worms of the original can be reverse-driven, the Kato single lead worms cannot. What this means in operation is going down a moderate to steep grade with a decent load of cars, the cars can “push” the locomotive with a double lead worm to go faster. A single lead worm with any longitudinal play will “buck” as the limits of the play are reached when the train pushes the locomotive. It looks like the installation was designed to combat this problem by ensuring the bearings are tight in the gear box through the addition of plastic bars.
As long as the longitudinal play of the worm is kept in check, the slower speed running is a huge benefit. Thank-you for sharing, I learned a lot.
Unfortunately, the current draw of an electric motor changes significantly with the load. This means that the voltage drop across a resistor in series with the motor will also vary with the load. This will make control difficult.
A better solution would be to use a fixed voltage drop with diodes. For example, a 1.5V constant voltage lighting unit drops 1.5 volts from the supply to the motor. Add another unit in and you have reduced the max voltage available to the motor from 12 to 9 V. And the first 3 volts of power pack do not go to the motor - it goes to lighting units. If your motor normally starts turning at say 3 volts from the power pack, it will now take 6 volts to make it start. When your control is at max, the motor will see 9V instead of 12.
