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I am going to replace the front and rear bearings. It seems I need to pull the idler gear first, in order to remove the drive gear from the end of the armature shaft.

Anyone with experience working on these? Am I going down the right path?

Post Title edited for clarity on what engine and motor this is.

Last edited by S Rice
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Some pictures to illustrate the problem.

The Schematic Drawing shows the two bearings I am replacing. The Gear Picture shows the drive gear and idler gear. How do you separate the drive gear from the armature shaft? There isn't enough clearance for me to get a gear puller on the idler gear, and with the idler gear in place there is no way for me to get one on the drive gear.

I have thought about using a wedge to insert between the armature coil and where the rear thrust bearing is, but I am worried that will damage the winding.

Any input is welcome.


Images (2)
  • Schematic Drawing
  • Gear Picture

The motor has a splined shaft securing the gear.  I have removed the brushplate, staddled the armature in a vise supported by field windings, then used a drift smaller than the shaft to drive the armature out.  

Why do you think you need to replace the armature bearings?  The idler gear generally wears out before the motor bearings.  Just pry the idler out with a small screwdriver.  Replacements are available from

Thanks Jon,

I originally posted the symptoms and observation in this post. And then after reading this one about a more modern pulmor motor (vertical, not horizontal), I realized my sounds were were very similar.

I decided to take a second look at my motors, and when I put it in the cradle inverted, the front motor made the noise 100% of the time after about 10v. There is a lot of play along the axis (side to side since it is horizontal), and laterally (nearly contacts the field, but not quite).

Further, when holding the motor vertically out of the engine, the armature for the rear motor spins freely for a second or two when spun by hand. I can even achieve this by using my thumb to spin the idler gear and the armature spins smoothly for a second or more. The front has a "wobble" that dampens and kills all rotation almost instantly after i finishing spinning.

Based on that, I assumed one of the bearings might be worn.

I can see my thinking on removal was backwards. I was worry about removing the gear from the splines, it never occurred to me to drive the shaft through. Based on that its easy enough for me to build a saddle and use press it out.

And yes - Jeff is the best for parts. I bought my bearings and other parts from him. I will always check him first.

**** - even if I am wrong, I love doing new things and learning. Should be fun.

All right - I expected that drive gear to be hard to get off, but even using my rivet press I can not get any movement. Anybody have an opinion about liquid wrench or other penetrating solvents (operating on the assumption there may be some oxidation/corrosion but I certainly dont know that for a fact). Or for that matter, other suggestions about how to free up the drive gear off of the splines on the end of the armature shaft?

This is only a guess but after removing the two 6-32 brush plate screws and brush plate put the two screws back in making sure the are sticking out far enough to rest the motor on them in a vertical position. Now use a small punch to drive the armature shaft thru the drive gear. Looks like that should free the armature from the motor housing.

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