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Request for advice on dynamo fitting problems

BlackLightning998

Well Known and Active Website User
VOC Member
Afternoon all,

Before commencing major surgery I thought I'd check if anyone has come across this problem before.

I have a made up dynamo which came on my bike when I bought it, it has a lucas shell grafted onto a Miller drive end. Thus gives you the slightly higher output.

I've just got it back from being rebuilt totally (I burnt it out) so it has a new armature shaft.

When I fit it all back together I can only get the nut half on the end threads.

The PD16 sprocket carrier is tight on the end of the armature shaft - so tight that my sprocket puller wont budge it back off. However there appears a bit of space behind it, between the PD16 and the bearing housing on the dynamo end. It looks to me as if the PD16 and the armature shaft are not compatible and the PD16 needs to move up the shaft a little to enable me to get three more threads on the end and secure the nut.

Comparing the distance from the dynamo bearing plate to the end of the threads on this dynamo and a spare that I have they are about the same - so it is unlikely that the problem is a short armature shaft.

(I know about the tab washer and drilling and wirelocking the nut too).

Has anyone come across this problem before and have any suggestions for me before I start surgery - I'm thinking that the PD16 needs to be eased to allow it to locate further up the armature shaft to give me the clearance I need. Looking at it, this will bring the sprocket central on the chain run and so position it properly too.

Any thoughts or advice gratefully received.

Many thanks

Regards

Stuart

PS The PD16 is the actual one I used on a spare Miller Dynamo that I borrowed and have been running with in the interim - it went on properly to the right place and I got the nut fully on as expected. So that might sugegst the PD16 is OK.
 

Len Matthews

Well Known and Active Website User
VOC Member
Stuart. it's quite normal for the threads on a Miller armature to be too short to get a full nut on. One solution is to take a normal 3/8" BSF nut, put in the lathe and turn off approx. half the hexagon so you are left with a 1/2" dia. spigot that will pass through Drive Plate PD17AS, the centre hole of which will have to be opened out to 1/2", then secure with Series D lockwasher,PD?
which already has a 1/2" dia. hole. This way the retaining nut will occupy more threads on the armature.
 

BlackLightning998

Well Known and Active Website User
VOC Member
Hi Len - which is the better solution?

Hi Len,

Thanks for your reply.

Would you think that the idea of recessing the nut in the centre of the drive plate is a better solution that easing the PD19 to sit further onto the armature shaft in order to expose more threads?

If I go the recessing route I think I will then need to mount the dynamo with a gap from the primary housing in order to have the sprocket sit dead centre on a run of the chain?

Cheers

Stuart

Stuart. it's quite normal for the threads on a Miller armature to be too short to get a full nut on. One solution is to take a normal 3/8" BSF nut, put in the lathe and turn off approx. half the hexagon so you are left with a 1/2" dia. spigot that will pass through Drive Plate PD17AS, the centre hole of which will have to be opened out to 1/2", then secure with Series D lockwasher,PD?
which already has a 1/2" dia. hole. This way the retaining nut will occupy more threads on the armature.
 

nkt267

Well Known and Active Website User
VOC Member
Hi Stuart.My belief,as I do not own a twin I cannot say that I know these parts,is try modifying the cheap and easy to replace items before looking at the more complicated and expensive bits..John
 

BlackLightning998

Well Known and Active Website User
VOC Member
Here's a picture of the problem:

Evening All,

Following on from Len's experience and advice I've been looking at my dynamo problem again. When I fit it all up right now, with the dynamo sitting up tight to the primary, the sprocket just touches the front face of the centre span of the chain - so it needs to go back by 1/16th (or thereabouts) to sit centre span, moving the dynamo back off the primary face. So I could do that by moving the dynamo back 1/16th or perhaps by moving the PD16 up the armature shaft 1/16th by easing it - however as you'll see from the picture there is more than a 1/16th needed to get the nut to sit home on a full thread. I have the clearance inside for the PD16 to go up the shaft and still remain front and proud of the inside of the primary - so the oil thrower will not foul.

Also following John's sensible logic, I only plan to modify the sprocket carrier (PD16) the drive ring and the nut - so nothing too disaterous to replace if it does not work.

I therefore deduce that to solve the first problem I have identified (can't get a full nut on) I would need to do both, move the PD16 and also the modify to have the turned spigot and recess for the nut that Len describes.

The drawing envisages having to have the dynamo off the primary as it offers three standard thickness's of PD19 spacing shim to slip on the end of the dynamo before it meets the primary cover.

However by moving the PD16 I will remove any forward play movement on the dynamo - i.e. if I then bolt it all up and have got the measurement wrong, then I risk the sprocket fouling the rear edge of the centre chain span and having no free play to move it forward.

I'm leaning towards having both done - and if I get the measurement wrong then I simply fit a new PD16 and I'm back to where I was, but with a recessed nut I have best chance of getting a secure fixing with loctite, a tab washer and perhaps even the mod of lockwiring the nut to a allen screw placed into the hole in the sprocket with loctite and filed off flush on the back face. By having both done I maximise my chances of getting a full set of threads through the nut.

Call me paranoid but I have heard of a few disasters with the nut coming off causing a chain lockup, snap and exit through the crankcase/primary cover. I was taught to get a full sets of threads through the nut - or risk a problem.

Any further thoughts or advice on the attached photograph or my notes above would be most gratefully received before I start work?

Regards all,

Stuart

Hi Len,

Thanks for your reply.

Would you think that the idea of recessing the nut in the centre of the drive plate is a better solution that easing the PD19 to sit further onto the armature shaft in order to expose more threads?

If I go the recessing route I think I will then need to mount the dynamo with a gap from the primary housing in order to have the sprocket sit dead centre on a run of the chain?

Cheers

Stuart
 

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bmetcalf

Well Known and Active Website User
VOC Member
I use a ring of adhesive-backed closed cell foam to seal that face, which also spaces the sprocket more central on the chain. I know that it has been said that the now-sealed space is there to let the chaincase breathe. If you want some of the foam, I can send you a piece.
 
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