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Lucas C40 dynamo


Colin Lindsay
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Can anyone confirm that there's no spacer or other attachment between the C40 dynamo body and the fan? My original fan has worn oval and on sourcing a replacement, the fan sits below the key on the drive so that there's nothing preventing it from rotating, unless it's just a matter of tightening the pulley so hard that it locks the fan in place? I don't want this one wearing away as well, but none of the diagrams I've found online so far show anything else. Second photo shows the fan in place and how far below the key it sits.

IMG_0417.jpg.061075406b494e06e3be73da1b1ce646.jpg  IMG_0418.jpg.ff89689a1728945fdcad085425b1e31a.jpg

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Colin there is indeed a spacer. It goes on first sliding over the key, up against the bearing inner race. Then the fan goes on with the blades facing the dynamo and positively located on the key. Finally the pulley the right way round so that the nut and washer clamp the whole lot in place...

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Ok so bought two... and they don't fit. Well they do but when fitted they foul the key on the drive, plus if I remove the key and slot them on they also seem to space the fan very far forward - a much bigger gap than I've seen before. Summat ain't right here...

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The spacer is sliding right along the shaft and up against the bearing inner race? It should enter into the end bracket and just protrude enough to allow the key to fit. It does require the bearing to be hard up against the shaft internal shoulder - could the rotor have moved inwards somehow? 

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On 22/09/2021 at 20:40, johny said:

could the rotor have moved inwards somehow? 

That's possible, but it's one of those tight-fit bronze bushes on the pulley end that cannot be removed once pressed into place (I think they're NLA anyway) and there does not seem to be any untoward movement.

The old spacer was right into the case:

IMG_0476.jpg.326275c6e033038dc43c81ad757e5cdb.jpg

The new spacer is deeper but still not deep enough to hold the fan into the key; first photo is where it needs to be, second is where it actually sits:

IMG_0475.jpg.e56a7dee048f1405a785378ebf5157da.jpg IMG_0474.jpg.46719c7d90599a1beb496bcc534023d8.jpg

There's no movement on the rotor at all when pushed or pulled. I may try to push the rotor bearing upwards back into the end plate in case it has moved outwards, but there may be wear through time and rotation that won't be overcome easily.

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Have you tried the key in place as it should have a curved base so that it actually extends beyond the end of the slot in the shaft. This may make it long enough to engage with the fan as designed.

What I cant understand is why the old spacer and new are different thicknesses (can the seller explain that?) and why the shaft sits so far out. The roller bearing inner race sits with one face against a shoulder on the shaft and the spacer on the other side so the position of the fan should never change...

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  • 2 weeks later...

Ok... might have got to the bottom of this, eventually.

There are different C40 dynamos and some have different characteristics.

The one I'm having problems with is a C40A, and it came with a very thick bakelite fan - this explains why the thinner metal one won't fit. It may originally have been from a Mini or even a tractor. The original fan was broken, hence the reason this dynamo is still with me and was never passed on.

I've managed to source another, which is a C40L - it should do the job and I'm leaving the fan in place undisturbed, just replacing the bushes and brushes.

In case you're wondering: the C40A was a smaller dynamo of about 11 amps output; the C40 we have is about 15 amps, and the C40L was a higher output version fitted to bigger engines (and possibly an optional extra on Heralds) and puts out 20 amps. The C40L has a longer body to incorporate more windings for the higher output. 

So: now you know!

 

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1 hour ago, johny said:

its the chance of exploding when I miss a gear

I've had one of the steel dynamo fans let go (on a 1500 Herald). Several of the "blades" fell off, fortunately without causing any obvious damage to anything that we could see, but the resulting imbalance made the car decidedly unpleasant. We swapped it for a dynamo with a bakelite fan, which outlived the car.

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1 hour ago, NonMember said:

I've had one of the steel dynamo fans let go (on a 1500 Herald). Several of the "blades" fell off, fortunately without causing any obvious damage to anything that we could see, but the resulting imbalance made the car decidedly unpleasant

Me too on the 13/60 when it happened it was very impressive and worrying, I thought the engine had exploded! No damage but the vibration! Took the remnants off until a replacement found.

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