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Discussion Starter #1
Hi Guys,
I am putting together an Aurora MT chassis from parts. I have noticed a problem which may be unfixable, but I want to check.

The gear train binds up; not every revolution, but frequently. In fact, if I put the car on the track it will go a few feet then stop and you can hear the electricity humming in the motor. When it's free, it's nice and loose. But there is a spot where it binds.

All the gears look okay. So I looked at the gear plate and see that the idler gear meshes very deep into the armature pinion gear, but barely reaches the rear driven gear. I have tried other idler gears, as well as trying this idler gear in another gear plate. The problem lies in this particular gear plate.

The obvious fix is to change the gear plate, but before I do that, I want to see if this gear plate is salvagable. My only option seems to be opening up the idler gear hole so the idler can move back a little. Any other ideas?

This is a Magna-Traction chassis, with a large hole gear plate. The idler gear is plastic.

Thanks...Joe
 

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Nip the offending gear stud off and attach the gear with a screw in the new location
or just reduce the size of the stud itself, front edge and rear edge, (now eye shaped)
to allow that gear to float forward and back without allowing side to side movement?
 

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Discussion Starter #3
Completely cutting off the gear stud may be the only option to make this gear plate useable, and if that's the case, the gear plate is junk. Making the gear stud into a "eye" shape wouldn't allow the gear to move back and forth since as long as there is one full length radius line left on the stud, the gear can't move.

I guess I have never run into this before, although until today I never bothered to check the gear mesh under a magnifying glass on any car (and still haven't checked all but one or two others). The binding comes from the fact the idler gear meshes so deeply into the armature pinion that it occassionally binds. The gear stud must be off center - that is the only explaination. The fact the idler can't reach the driven gear means something is wrong.

Thanks...Joe
 

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I think it's probably junk unless you redo the idler post as suggested.

A couple of things you could try just for grins:
1) reduce the od of the motor pinion gear by sanding it down. Remove idler and just rev the motor while holding fine sandpaper to the OD of the pinion gear. This will take off some of OD and might make it mesh better.
2) replace the 14T with a 12T 'hop-up' gear (but if this works, you've just geared-down the car so it'll go slower (but more torque!)). If you can find a 13T gear it might be ideal but no idea where you could find one of those. Maybe RT-HO would make one for you but he does not list it online.

Good luck.
 

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Discussion Starter #5
I think I discovered the problem and the gear plate should be salvageable.

I noticed the rear gear was a little loose, so I tapped down the rivet just a bit. This reduced the amount of "play" in the rear gear and also brought it closer to the idler (now it can't get cocked off-plane), enough so that the mesh is acceptable. I was surprised this worked, but it did.

Before I did this, I could turn the rear wheels and the rear gear would slip on the idler, only occassionally meshing. After tapping down the rivet, the mesh is much improved. Still had to change the idler as it meshed too deeply in the armature pinion, but I had a few extra lying around.

Followup question - if the rivet is too tight, how do you loosen up the rear gear without breaking something?

Thanks...Joe
 

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07-05-2012, 11:49 AM
LDThomas

The problem is...
The rivet holding the cluster gear is probably not fully seated. (I have had several of those.) The fine pictures provided look to me like the rivet is sitting a bit high. That allows the cluster gear to slide up and away from the crown gear. If you can pull the cluster gear up on the rivet, you will need to seat the rivet so that it holds the cluster gear in the proper location and re-set the rivet.

.
 

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The backyard mechanic in me says gently slide an exacto knife between the gear and top plate, just once on each side of the gear, and watch yer fingers!
 
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