Dynamo mounting

[John B.]

Engine 1948 G3L. I have the dyno. off at the moment to try and breath life into it! The inner chaincase has where the shaft intrudes a 1 5/8" plain hole. No seal of any kind is evident tho. there are three 1/4" holes surrounding the main hole. Whilst on subject the dyno sprocket has 17 teeth as does the drive one behind the main primary drive. The chain has 47 links ( with, obviously a crank link in it). Does this sound normal? I had no charge from dyno. (E3.AR. A05-1). Now off machine and cleaned up brushes ect. it does motor when connected to battery as prescribed in Lucas notes. BUT in opposite direction to arrow, eg clockwise from drive end! Reversing battery polarity has no effect, still goes clockwise.Any comments about this? Thanks John B.

[Groily]

Need to swap the brushes round, or the field coil wires John, but not both or you end up where you started.
It can run whichever way at whichever polarity you select, regardless of arrows etc.
The sure-fire way to get the right rotation and the right polarity while it's off the bike is to motor it from a battery earthed the way you want, while seeing it go the way you want it to. Motoring it sets the polarity, gives you visual proof of which way it wants to go, and also proves that it does actually turn.
Motoring is, however, an imperfect test because simple inertia can make the thing skate over a dodgy winding. A better test it to apply some load - like a headlight bulb - and see if it lights up. To do which, bridge D and F terminals at the dynamo, connect bulb between bridge wire and earth (see loads of posts here), rotate dynamo the right way in drill or whatever. (Battery-powered ones often don't go fast enough, but a mains-powered one will.)
As you'll see in the Lucas service notes, it's not a great plan to re-set polarity by pressing the cut-out when the thing's hooked up (although it does the job) - far better to polarise directly from the battery to the F terminal. That way, you don't stress the insulation etc of the armature. But not necessary at all if you've set it up by motoring and have tested it for output under load.Edited by - Groily on 17 Jul 2011 6:15:31 PM

[John B.]

Thanks Groily will give that a try as soon as poss. John.

[wilko]

Report back immediately. I love dyno talk. It's quite satisfying getting one to work without the expense of a rewind.

[John B.]

Right Wilco and thanks Groily. Bin out and swopped brushes. Amazing , it runs right way now. AND......... have lots of volts on my super moving coil volt meter. Only thing is can,t check it under load like wot you recommend because would you believe it, my dear wife won,t go the 30 yds through the rain to my shed to help me hold all the bits together!. Still looking very hopeful. John.

[wilko]

Get her to use a brolly and hold the light globe and wires!I'm sure it will work.

[Groily]

Lots of volts is probably good John - I also bet it's fine now. No need to importune the Dear One probably!

[John B.]

Thanks chaps, yes it lit up both part of a stop tail bulb like Christmas. Could probably put a prop on it, mount it on the roof and heat the house. John.

[laxy]

Hi John, when refitting the dynamo to the bike the chain must be endless.The primary and dynamo chains pass very close to each other and if they kiss when the engine is running.............

[John B.]

Hi Laxy, it is endless but has this curious little crank link making it 47 links. I just wondered if this was a standard feature.Both engine and dyno. sprockets on mine have 17 teeth. Have seen,on e-bay, engine sprockets with 21 primary drive and 21 dyno. drive teeth for sale. This set up would need a longer chain, and it would speed up the dyno? John.