I've just noticed what I am guessing is some pitch type insulation substance leaking out from the dynamo. Same end as the mag points. Obviously I am going to have to check it out, but before I start taking it in to a specialist for it to be sorted has anyone had this problem and what is likely to be the cause? I dont want to be taken for a ride by the repairer telling me it is something far worse/costly than what it might be. And conversely I dont want to fobbed off with some quick fix if it is likely that something more serious is the prime fault. Any suggestions? cheers.
Duncan

Hi Duncan..There is no 'pitch' inside a dynamo or anything directly compatible to that material.
Original windings are shellac coated and there are the carbon brushes. Also, in a WD dynamo the brush end casting has an oiled, oilite bush fitted, not a bearing. So, breakdown of the shellac, carbon dust from the brushes and oil/bronze from the bush may be combining to produce the effects you have.
If the problem is recent it may be that the dynamo is overheating if it has a fault...or that your regulator has a fault causing the dynamo not to 'cut out' when the battery is fully charged and there is no other load on the circuit.
Alternatively you may have a battery fault..The small lead acid batteries frequently fitted these days accumulate sulphates on the plates when left standing for long periods. If this occurs they will not hold a charge and the dynamo will charge continuously as if the battery was 'flat'. It is not designed to work like that and running at constant load will cause it to overheat..If you are UK based I can do the dynamo for you if required and you will only get what you need..However, if the dynamo has a fault and is an old one you will probably need most of it
. The field coil windings rarely fail and can be reused if undamaged, but most other components usually require replacement. Most providers don't do repairs as such but overhauls..they have learnt the hard way that if a dynamo fails after a repair, even if the fault is not related to the repair, the customer will always regard it as down to the repairer. Consequently most are not keen on returning a unit with a high content of worn/used parts in it..I learn't a long while back with engine work that saving money for your customer can be an expensive exercise, as I am expected guarantee the performance of the resulting job. As a result I build engines etc. to a specification, not a price, though I don't set out to 'fleece' anyone....Ian

email (option): ian@wright52.plus.com

Hi Ian thanks for the prompt and informative reply. 'Pitch' was the best description I could come up with for what the stuff looks like and as I've never had one of these to pieces I just assumed that old Joe Lucas stuff might have had something along those lines as insulation. Yes, I would agree that overheating has been the cause although I wasn't aware of it when las t running but will check when I take it out again. I think I can rule out sulphates on the plates as, although I have small battery of the type you mention, it seems to give sterling work even when the bike isnt running so I dont think it is duff (yet). I will read some books then check out the regulator as best I can to see if that is at fault. It is an old, maybe original, unit so it is perhaps overdue for giving up the ghost! PM sent.
Duncan