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Centurion Rotax Starter Question


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I just rebuilt a Rotax starter for a Meteor engine, but not successfully. One of the brush springs is weak so there is lots of sparking when I test it unloaded. The rotor spins very quickly unloaded and has quite high vibration so I think the brush is bouncing on the commutator.  I can see signs of previous overheating on the insulating disk the brush assemblies are mounted on at the weak brush on so I suspect that brush assembly overheated in the past and softened the spring. I can reduce the arcing by gently pushing down on the brush with my finger. I have moved the spring end to the furthest "tooth" on the brush arm to get the maximum tension. 

The brush assembly can't be removed easily because the starter end cover and casing are integral. So to remove the brush assembly, you have to remove the field winding assembly. And it doesn't want to come out. 

Unloaded, the starter pulls about 35 amps. Loaded, I would expect it to pull 150-200 amps, so I suspect the bad brush would arc so much, the starter would fail. 

Anyone have any suggestions? 

Also, the two terminal studs are not marked for polarity. The nameplate says the starter runs CW.  And it does, regardless of how I connect the power. So I assume reversing the polarity reverses the current through the field winding and the armature, which cancels the effect. Can anyone confirm terminal studs can be connected either way? The manuals I have have no comment on this. 


Edited by sexton
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  • 1 month later...

Yes I had the starter completely dismantled. It doesn't surprise me it vibrates when spinning unloaded, water had got in and caused some rusting of bearings and gears. We don't need a working spare right now so I'll keep it for parts. 

Thanks for the confirmation on the polarity.


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