Dynamo stopped working (due to dirty armature)

[KiwiGF]

Here's a 'lesson learnt" of......... "don't miss the obvious"  

Whilst running in my newly built bike it got dark and I found the charging had stopped at some point, so I lost the lights 20 mins after turning them on. I ended leaving the bike at my brothers and borrowing a car to get home

During the rebuild I had put new bearings in the dynamo, cleaned it all up, and it tested out just fine on the bench using a drill to spin it and a mechanical regulator connected up which charged a 6v battery and ran a headlight bulb at the same. I fitted the dynamo and a DVR2 unit....and the charging was fine...at least for some of the 600 miles of running in  

Before giving up and borrowing the car I tried the test of joining the field and armature connections together and started the engine, but the dynamo was not generating any volts between the connections and earth, so I concluded the dynamo was at fault and I was not going to be able to fix that at my brothers place.

So, after going the get the bike the next day (in daylight) I removed the dynamo and this is when things got "interesting". Joining the connections and spinning the dynamo using a drill it would generate up to 16 volts whilst lighting a 12v headlight bulb eg the dynamo seemed fine.

The dynamo would also run fine as a "motor" when connected to a 6v battery and the resistances of field and armature all measured OK.

The PROBLEM was that it seemed to me that the dynamo needed too many revs from the drill to start "self generating" almost like there was not enough "residual" magnetism in the field coil.

Anyway, after much messing about with the wires under the dynamo's cover (as I thought they must be shorting to earth) I fixed the problem by CLEANING the armature and brushes and on the bench it started self generating at a much lower rpm.

The armature did not look that bad and I've no idea why the armature had got dirty at all, within 600 miles of it being cleaned during the rebuild, but that cured the problem and the charging is working fine now.

If it happens again at least I will know what to do to fix it, and I will then get new brushes as maybe they have degraded in some way.

In other posts people have had problems with having to reflash the field multiple times to get the dynamo to work, but I wonder if the issue they had was actually a dirty armature?

[muskrat]

G'day KiwiGF. When you say armature I think you mean the commutator. Was it dirty from carbon? The brushes might be past their use by date.
I rebuilt the dynamo on the '51 thirty odd years ago, that's the last time it has been looked at (apart from a belt conversion 5 years ago). I need mine to be good to run the 12v electronic ignition and halide headlight.
 The only things in there that can create dirt are the brushes or if the armature rubs on the field coil (loose screws).
If it happens again in a few hundred miles I'd replace the brushes. Glad you got it sorted.
Cheers

[KiwiGF]

Yep muscrat yr right i meant commutator but i could not spell it 

Yep black carbon and i think ill get new brushes as you made me realise in 600 miles there should not have been ANY wear on the brushes so they must have gone soft or something

Thanks for yr help!

Simon

[bikerbob]

Another reason could be that you are not making the dynamo work hard enough. A good number of years ago when I restored an A10 I had the dynamo overhauled but after less than a thousnad miles it stopped working. I went back to the chap who helped me and he told me that a dynamo needs to work hard by that he new that I was only riding during daylight and not using the lights at all. He advised stripping the dynamo down cleaning the commutator up then rebuild it up and when out riding during the daytime put the lights on for at least 50% of your journey and you should have no further problems. I did as he suggested and that dynamo ran for a further 15 years without any further problems.

[wilko]

Hmmmmm....? I haven't worked hard for years now but still here!

[KiwiGF]

Hi biker bob ill give that a go ...at least ill know if the dynamo packs up again before i need it to be working!

I got it back on the road today after 2 months waiting for parts for the gearbox etc great weather and dry roads now up to 750 miles on the new engine but yet had to take the primary case off afterwards but that might turn out to be a plee for help n the gearbox/primary section......the primary chain keeps getting too tight

[bsa-bill]

.the primary chain keeps getting too tight

interesting - chains do stretch but not often shrink so something is moving
 2 obvious ones would be the gearbox and/or the rear wheel

[metalflake11]

Usually the primary chain tightens because the drive chain is too tight, and it is dragging the gearbox backwards.
 I am assuming that you have set the free play at the chains tightest spot in the first place?

[Triton Thrasher]

.the primary chain keeps getting too tight

interesting - chains do stretch but not often shrink so something is moving
 2 obvious ones would be the gearbox and/or the rear wheel

If the gearbox is not held securely, the rear chain drags it back, overtightening the primary chain.

It's good to have a gearbox adjuster on the drive side. Also, do the final adjustment of the primary chain tension by having the pivot and the sliding stud half-tight and making the adjuster force the gearbox forward. Then tighten the studs. That way, the adjuster is holding the gearbox forward.

[iansoady]

Also, do the final adjustment of the primary chain tension by having the pivot and the sliding stud half-tight and making the adjuster force the gearbox forward. Then tighten the studs. That way, the adjuster is holding the gearbox forward.

What he said. People usually take up a bit of slack in the primary and then tighten everything up - this allows the gearbox to move back slightly creating the problem.

[muskrat]

 ??? ??? We got two topics mixed up here. From bsa-bill on it's the primary topic.
Cheers

[bsa-bill]

We got two topics mixed up here

More a case of progressed from one to another as KiwiGF introduced the chain problem, proves us guys can multi task see