The standard Heng Long metal gearboxes can be very noisy and sometimes prone to stripping a gear, this is a brief HOWTO improve them by shimming and bedding them in with grinding paste.
First off remove your gearboxes from your tank - see other posts on opening up and removing tracks / drive sprockets.
Undo the screws holding them down (usually 3) and remove from tank hull after unplugging the motors.
Remove the motors from the gearboxes by removing two screws in the end of each motor by putting a long thin pozi or cross head screwdriver through the holes in the opposite side of the gearbox. NB If you have older boards with soldered motor connections you may need to do this before you can remove the gearbox from the tank.
You should now have a pair of gearboxes like this
- twogearboxes.jpg (59.62 KiB) Viewed 3861 times
To undo the gearboxes you need to remove two screws on the bottom and two screws into the braces on one side
- screwpositions.jpg (40.84 KiB) Viewed 3861 times
Screws removed
- screwsout.jpg (38.57 KiB) Viewed 3861 times
And separate the side from the gears
- separated.jpg (41.74 KiB) Viewed 3861 times
As you can see the gears are touching each other due to the amount of play in the gearbox
- gearstouching.jpg (55.23 KiB) Viewed 3861 times
Take the gears out of the bearings ready for shimming
- gearsremoved.jpg (45.77 KiB) Viewed 3861 times
Place 4mm brass washers on the shafts on alternate ends to shim the gears
- washersinplace.jpg (57.71 KiB) Viewed 3861 times
And re-assemble into the gearbox bearings
- gearsbackinplace.jpg (55.46 KiB) Viewed 3861 times
Replace the gearbox side and re-insert the screws - if the gears bind it may be necessary to add washers to the braces, I use 3mm brass washers just because I have them available.
- bracing washers.jpg (44.93 KiB) Viewed 3861 times
You can now see there is good clearance between the gears with the washers on alternate sides.
- washersandclearance.jpg (50.31 KiB) Viewed 3861 times
Now its a matter of using grinding paste or other mild abrasive (toothpaste has been used) to smooth the gear teeth where they mesh, put small amounts of paste on the gears and attach a drill to the output shaft, run the drill alternately forwards and backwards for about 10 minutes which should be enough to smooth the gears where they mesh, once complete, strip down, clean off the grinding paste (I wash with paraffin) and reassemble with your chosen grease for lubrication.
Hope this is helpful.
