Author Topic: Quality of Carbon brushes?  (Read 1121 times)

Offline LJ.

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Quality of Carbon brushes?
« on: 17.01. 2013 10:28 »
How do you know if your dynamo brushes are of the correct hardness? Is there a 'penknife scrape test' one can do or do you just have to fit them and either, expect to have to clean them regularly if they are too soft or suffer arcing (spelling?) if they are too hard?

I am finding my M21 60 watt long dynamo is having to be regularly cleaned and its becoming a nuisance. I've often wondered about cutting up some old brushes from burnt out motors that I have. Has anyone done this? Success?

And who reliably sells *Good* long lasting brushes if home made ones are not the way to go?
Ride Safely Lads! LJ.
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1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
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1961 BSA A10  650cc Golden Flash-Red

Offline a101960

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Re: Quality of Carbon brushes?
« Reply #1 on: 17.01. 2013 11:48 »
L.J.

You need to buy from a dynamo repair specialist.  Dave Lindsley, Tony Cooper, and Sean Hawker are just some of the suppliers that spring to mind. A rough test to determine if a brush is to soft is to try writing with it. However also be aware that there are some brushes around that are to hard. I don?t know how you can test for that.

John

Online bsa-bill

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Re: Quality of Carbon brushes?
« Reply #2 on: 17.01. 2013 12:05 »
not sure how a brush can be too hard John unless it gouges out a track in the slip ring in which case maybe it's more the spring, however as usual I look forward  to being informed
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline a101960

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Re: Quality of Carbon brushes?
« Reply #3 on: 17.01. 2013 12:36 »
Bill,

There are degrees of hardness due to the manufactoring process. It is a complex business (baking time, pressure, and formulation). There was aproblem a while back where grooving happened due to hard brushes. As ever the problem lies with where the parts are sourced from. Some classic bike spares suppliers are not always technically aware. I agree with you that spring pressure could be an issue.

John

Online metalflake11

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Re: Quality of Carbon brushes?
« Reply #4 on: 17.01. 2013 15:15 »
 Brushes that are too hard are also too brittle and tend to fracture. I have no idea how to test for that, other than some sort of crush test on a random brush in a batch they are making?
England N.W
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Online bsa-bill

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Re: Quality of Carbon brushes?
« Reply #5 on: 17.01. 2013 19:49 »
Thanks guys, the grooving I had thought about but not heard of any cases, brittleness now that I had not considered
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline BSA_54A10

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Re: Quality of Carbon brushes?
« Reply #6 on: 17.01. 2013 23:39 »
Bosh brushes are too hard for Lucas magnetos.
Found that one out the expensive way.
Brushes that are too soft will wear quickly and leave a lot of graphite dust inside the maggy so you will be forever cleaning it out and putting up with misfires due to arcing.
Bike Beesa
Trevor

Offline wilko

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Re: Quality of Carbon brushes?
« Reply #7 on: 18.01. 2013 22:07 »
Why aren't Bosch brushes too hard for Bosch maggies? 

Online bsa-bill

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Re: Quality of Carbon brushes?
« Reply #8 on: 19.01. 2013 11:29 »
Quote
Why aren't Bosch brushes too hard for Bosch maggies? 

Could be down to the springs Bosch use Wilko and the material in the slip rings,  not trying to causes an international incident but the most trouble I ever had with sparks was with a Bosch distributor on a Ford Fiesta, under warranty the garage had three goes to cure it (poor performance , missing ), I (I take a bow at this point) eventually suspected the thing was moving in the clamp, so five minute with a file to enlarge the gap in the clamp and it was cured.
All the best - Bill
1961 Flash - stock, reliable, steady, fantastic for shopping
1959 Rocket Gold Flash - blinged and tarted up  would have seizure if taken to  Tesco

Offline BSA_54A10

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Re: Quality of Carbon brushes?
« Reply #9 on: 20.01. 2013 11:47 »
Lucas slip ring contacts and commutators are softer than Bosh ones.
Lucas springs press harder than Bosh ones.
Horses for courses.
Hard brushes pressing against hard contacts will run for longer before needing replacement
Bike Beesa
Trevor