Joined: Aug 2017 Posts: 622 Threads: 19
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Location: Hampshire UK
I'm dredging my memory a bit here, but I recall that the "earthy" starter brush connects internally to the starter body via a riveted connection. Its not impossible for this to look OK and be nice and tight but have corrosion under the mushroom head, which raises the resistance of the connection. Bear in mind that starters can draw hundreds of amps and you need to keep resistance extremely low if it is not to drop significant voltage.
The only way to reliably test such a low resistance is to pass a known medium current through it, say 5 or 10 amps, and measure the voltage drop with a sensitive voltmeter. A car battery in series with a spare headlamp bulb will make a crude current source.
I resorted to soldering a copper link across one riveted joint, to save taking it apart.
Joined: Oct 2017 Posts: 1,536 Threads: 55
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Unlike dynamos starter commutator segments are not under cut.
Joined: Dec 2017 Posts: 1,160 Threads: 68
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Location: Nottinghamshire. Robin Hood County
Car type: Austin Ruby Mk1 1935
Dave could you enlighten this dumbo on what is meant by under cut in relation to dynamo commutators .
Thanks.
John Mason
Would you believe it "Her who must be obeyed" refers to my Ruby as the toy.
Joined: Oct 2017 Posts: 1,536 Threads: 55
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After skimming a dynamo commutator the insulation between the commutator segments is cut down for which I use a modelling saw.
Joined: Apr 2018 Posts: 192 Threads: 76
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Think I'm about to give up on this.
I've now thoroughly cleaned up the commutator and fitted the new brushes but there's been no improvement in the motor at all.
Runs smoothly enough but with no real power so I suppose it must be an electrical fault but I've not been able to find much in the way of an "idiot's guide" to checking this out.
I assume there should be continuity through the field windings and they shouldn't be down to earth. I haven't tried to check this but if it were the problem then would the motor work at all?
I seem to recall that each segment of the commutator should be connected to just one other so I guess I could check this although again I'm not sure exactly what I'd learn from it.
Do the new brushes need to "bed in" or am I clutching at straws?
Just getting really annoying that I don't feel I really understand what issues I'm looking for.
John.
Joined: Aug 2017 Posts: 1,539 Threads: 61
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I had a similar experience so gave up and adapted a modern starter to fit
Charles
Joined: Aug 2017 Posts: 1,658 Threads: 23
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Location: The village of Evenley
Car type: 1934 Austin Seven RP Deluxe
I’ve just had exactly the same issue as yours John, Motor spins, but has absolutely no grunt to throw the Bendix in.
The front plain bearing was a bit slack so I’ve machined up a new one. The new brushes, I have bedded in by wrapping the commutator with 150 grit wet or dry and spinning it to get a good connection. I have also thoroughly cleaned everything including the oil on the Bendix, which i’m Sure didn’t help, replaced the broken Bendix retaining clip and carefully filed the copper connection, which was burnt, on the starter switch for a better connection.
If you can be patient while I wait for my neighbour to lend me his heavy duty jump leads, I’ll let you know if it works!
If it doesn’t I’m going to do a full and detailed electrical check (my neighbour is an electrical engineer, so i’ll Ask his advice, from a safe distance of course) to see if there’s something inherently wrong and report back either way.
Don’t give up, there c@nt be much simpler than a starter motor...can there?
Joined: Aug 2017 Posts: 1,031 Threads: 54
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Location: The delightful town of Knaresborough, North Yorkshire
John P, have you tested the motor on the bench yet, completely away from the car?
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John
Just reading again your dilemma.
I have a question for you, are you sure the battery is OK ?
As it only reads 6.2 volts it sounds below par.
I am deeply suspicious of your battery, if it has just been charged and stood for 12 hrs it should read about 6.4 volts.
Have you the means of stress testing it or have you got six volt battery which definitely OK to try ?
I hope this does not stress you further.
