Starter Motor Issue

[John Cornforth]

Hi

I think starter brushes are often a copper/carbon mix, possibly copper plated on the outside. The resistance will be lower than carbon only.

The dust you have removed may have been partially shorting the segments, or maybe dismantling and reassembly has improved the contact pressure. Glad you are now sorted.

[Dave Mann]

    That brush looks to be well worn here's a new brush Graham.

[Graham Barker]

Hi Dave,
Thanks for your photo.  My camera angle is a bit misleading.  There is quite a lot of useful depth of brush left, although not as much as yours.  The brush has seated at a bit of an angle but has worn itself to sit nicely on the commutator at that angle.  Nice to know that someone else has the same type of brush.
Regards
Graham.

[Jeff Taylor]

Graham, in my almost 50 years messing about with Morris cars particularly 1930's Morris 8's, these copper compound brushes appear to be universal in all Lucas Starter Motors of this era. Purely carbon brushes are only used in their Dynamos.

[Graham Barker]

I guess that copper is needed for the heavier current that occurs in starters.

[Dave Mann]

    My friend is having starter problems with his standard RN saloon, I've rebuilt two starters and both fail to start a cold engine so I've lent him one of my starters which I know is good. I've got one of his motors back and the photo shows burn marks on the commutator this is on a 6 volt car. He has replaced all the starter cables with nice new big ones, has anybody any ideas as to the cause of the failure to turn over a cold engine and the burn marks?

[andrew34ruby]

Would it have benefited from some running with no load, to 'bed in' the brushes? With no load it would spin faster, so less current.

[Steve Jones]

Don't know why it won't turn over the cold engine, Dave, but I had a starter at one time that developed similar burn marks. Have to confess it was my fault as I'd let the brushes run down to the point that the steel brush holder was touching the commutator resulting in signficant arcing that burnt the commutator. Didn't do anything to it other than basic cleaning up and a pair of new brushes and it continued to work fine for years after (and still does as far as I know).

Steve

[Dave Mann]

He reported that my good motor isn't any better so after checking the shaft wasn't bent I fitted his motor to one of my engines and it ran perfectly on 6 volts. I conclude that a previous owner has built up the ring gear by welding and some of the teeth are oversize, a problem I came across some years ago.

[Dave Mann]

I was partly right, the previous owner had a new ring gear fitted about 30 years ago when he rebuilt the engine since when it was never run unfortunately it was the wrong ring gear, it had the correct number of teeth which were 0.040" too wide and 0.060" too shallow.