The Cessna 120-140 Association Forum

Now and again I get a problem with my Delco generator... It stops working because of brush deposits on the commutator.

I clean it off and all is good again.

The brushes have quite a lot meat on them, but the contact end is now curved to the same profile of the commutator... Should these be re-profiled to form the 45deg angle of a new brush or do they just need replacing or is there something else going on?

7698 wrote: ↑Sat Jun 01, 2019 2:43 pm...the contact end is now curved to the same profile of the commutator...

That's normal. Now maybe they won't continue to wear as much.

I know this may seem like a Dumb question. (Which I'm good at) But,
How do you "clean" the commutator?
And, BTW, John C is right.
Steve.

5099 wrote: ↑Sat Jun 01, 2019 10:20 pm I know this may seem like a Dumb question. (Which I'm good at) But,
How do you "clean" the commutator?
And, BTW, John C is right.
Steve.

I clean it up with scotchpad which works fine... However, I seem to be doing this quite frequently so think that there is some breakdown in the brush material... or perhaps its just normal, but I dont here the alternator users doing the same..

7698 wrote: ↑Sun Jun 02, 2019 11:26 am I dont here the alternator users doing the same..

Is the commutator smooth? If not, you can smooth it with crocus cloth. Are the insulators sticking up between the segments? If so, they need to be cut back so they don't contact the brushes.

The biggest differences between the generator and alternator is the generator brushes carry the charging current whereas the alternator brushes only carry the exciter current and the generator brushes make and break between segments whereas the alternator brushes don't.

Hi John,

Everything is pretty smooth... Had some 400 emery cloth around the commutator a while back.

Just wondering if the blast cooling tube plays any part in the material pickup problem? Its not connected to anything as there is no fitting on the baffles in my set up...

Could it be getting too hot and the brush material starting to get sticky??

7698 wrote: ↑Sun Jun 02, 2019 1:05 pmJust wondering if the blast cooling tube plays any part in the material pickup problem? Its not connected to anything as there is no fitting on the baffles in my set up...

You really should hook it up. The generator doesn't have a fan so, absent the blast tube, there is no airflow to cool it.

Could it be getting too hot and the brush material starting to get sticky??

No, they're not made of anything that would melt at normal temperatures. Sticky material might be from the windings of the generator, in which case fix the blast tube sooner. Otherwise, look at the generator oil seal.

Thanks all,