Dynamo issues

[AndrewM]

I've been recommissioning my 1946 16M over the past few month, but have been putting off doing anything about the dynamo until last. I've failed to see any sign of charging on the ammeter whenever I've started the bike, and assumed that the problem would go away either when I flashed the dynamo or replaced the regulator with a solid state reg.

A couple of days ago I flashed the dynamo based on the best advice on here and from the supplier of the solid state reg. So I'm pretty sure it was done correctly. No difference on the ammeter when running.

Today I swapped over the regulators. Still no difference on the ammeter.

The ammeter appears to be working as it shows a negative current flow when I turn on the parking lights, and a greater negative current when the headlight is turned on.

So, what is my next step in diagnosing the issue? Or should I just assume the dynamo needs refurbishing and pull it out. Is there any other possible fault I should be looking at? Possible bad connections? And if so, how to track them down?

Should mention that I know the field coil was replaced in 1995 when the bike was restored, and the bike hasn't done much mileage since. So while that is 28 years ago, at least the field coil isn't 76 years old.

[SPRIDDLER]

To save typing out the various test procedures have a look at the link below which is well written and practical.

https://www.matchlessclueless.com/electrical/lucas/

[clive]

I put the dynamo back in my twin last night after having to replace the armature. Finally started the bike and was disappointed to find no sign at the ammeter of charging even blipping the throttle, was about to pull it all out again when I thought to turn the headlight on. Sure enough at tickover a discharge but up the revs a bit and the ammeter returned to zero, the battery was fully charged hence no apparent charging when no power was being drawn. So I proceeded to fit the cap (its a twin so you can do this it situ) and checked the charging, nothing. Cap off again and I realised that I had just caught one of the brush wires pulling and reducing the tension of the brush contact. More careful placement of the wires and cap and charging returned. Tricky stuff electricity even at 6 volts.

[AndrewM]

Thanks Spriddler, that's just what I needed.

[AndrewM]

I've gone through the dynamo diagnosis steps on the Matchless Clueless site with the following results:
1: disconnect green and yellow wires from dynamo, jumper the two sockets together and measure voltage between these and earth at engine idle. Results: zero volts
2. remove jumper and measure resistance between F terminal and earth. Result 2.8 ohms
3. measure resistance between D connection and earth. Result 4.7 ohms
4. reinsert jumper between F and D terminals, hook up a lightbulb between terminals and earth with bike running. Result, no light, clearly zero volts

So dynamo appears completely dead despite reasonable resistance values.

I thought one possibility might be broken brush connections, so I took the cover strap off and confirmed that there appear to be no broken connections to the brushes. However I am concerned if I disassemble in-situ any further to get a closer look I won't be able to get it back together.

So it looks to me like I need to remove the dynamo from the bike, but how the hell do I do that? I took the outer chain case off to look at what is involved and was horrified at the magnitude of the task. Is it possible to remove the dynamo on this bike without removing the primary chain, clutch and inner chain case? Is it possible to get the dynamo out the other side by taking off the primary chain and moving the gearbox rearwards?

Looks like a mechanic's nightmare to me, advice would be welcome

[SPRIDDLER]

Chill, Andrew. Removing the dynamo is simple with very little dismantling. It helps to remove the primary chain but no more is necessary.
In short, you remove the dynamo sprocket and withdraw the dynamo to the k/start side of the bike. No need to disturb the rear chaincase or clutch parts.

A first check would be to see if the brushes are in contact with the armature and move freely in their holders.

[AndrewM]

I'll take your word for it, but it sure doesn't look like it will come out that way. Anyway, I'm going to reassemble everything for the time being and do without the dynamo for a little while, I've got a good battery and LED lights so can do without it for the time being, particularly as its summer here.

In the meantime I will probably order this complete repair kit https://www.rexs-speedshop.com/product/ ... 30-20017a/ and get it shipped to Australia, and get my workshop set up to do the Dynamo refurb properly. Can be a job for winter.

[SPRIDDLER]

Hmm, perhaps I've brain fog, but this is the dynamo on my '47 Ajay and although it was a long while ago I don't recall having to remove the rear of the chaincase (but it's possible I'm confusing it with my '54 model ) .

Dynamo 47 Ajay.JPG

[ajscomboman]

You're not wrong Spriddler, all dynamos on singles are removed from K/start side and nothing more than the sprocket and chain needs to be removed for it to be extracted. Bit of wiggling might be required to line up the alinement bracket (if it's got one fitted) with the small slots on the engine plates All the drive side and rear chaincase remain intact.

[AndrewM]

Thanks for the confirmation gents, I was getting a bit concerned at the prospect of having to remove the clutch and inner chain case. Will get myself prepared and will try to do the whole thing fairly quickly in a few weeks time.