Dynamo Bearing Replacement

[rsawatson]

Not sure whether this should go under 'electrical' or here, but I decided that strictly it is a mechanical problem...

My dynamo bearing needs replacing. I had a go at it today, but could not for the life of me undo the nut which attaches the pulley wheel to the armature shaft. Has anyone got any suggestions/tips for getting this off? The nut is extremely stubborn and of course the shaft wants to rotate every time I try to hold the nut. I did get a friend to secure the opposite end of the shaft with a pair of mole grips, but this didn't work and the shaft still span.

Anything more I can do? If at all possible, I do want to avoid having to buy a new dynamo...

Cheers.

[bmcecosse]

It needs a short sharp shock - and yes it is difficult to do that without ruining the pulley....... I believe some wrap an old fan belt round the pulley and then trap the ends of the belt in a vice - so holding the pulley that way - but can't say I have ever done this........

[rsawatson]

Thanks... yeah I've just been looking elsewhere and saw the idea of using an old fan belt. I have been recommended that if I do buy a new dynamo, the voltage regulator should be replaced as well - as there can sometimes be problems. Providing it's been polarised correctly, should there be any trouble, or should they be replaced together?

[bmcecosse]

Nonsense - assuming it was charging ok and you are sure the problem lies in the bearings - the regulator will be fine. Who comes up with these mad ideas???! But - this could be the chance to upgrade to an alternator ! Try to get one in a scrappy - as others on here know ad nauseum - I used to buy them for £1 - but they are a bit more these days.....

[mike.perry]

Are you sure that it is the front bearing and not the rear bush that needs replacing?

[Alec]

Hello Ryan,

as you are having to dismantle the dynamo, remove the back plate and brushes, then the stator and grip the armature in a vice then undo the nut.

Alec

[bmcecosse]

Grip the armature very very carefully with much protection if you are going that route!

[Alec]

Hello Bmce,

the armature, despite being laminated is quite solid and is not easily damaged, so is not as risky as it may sound.

Alec

[katy]

Ditto

[bmcecosse]

The clearance to the pole pieces is pretty tight - any distortion will spell truble..... Actually I wonder at the wisdom of doing the job at all since dynamos can easily be picked up for a Fiver or less!

[Alec]

Hello BMCE,

if you can distort a dynamo's rotor in a vice you must have some exceptional strength? The other point about buying a second hand dynamo is that it may well be in equal or worse condition than the one it is intended to replace. I prefer to evaluate condition and then overhaul or scrap depending on what is necessary to restore it to serviceable condition.

Alec

[bmcecosse]

That nut can be VERY tight to undo........ So a long lever could be applied to the spanner..... I have some spare dynamos buried deep in the garage - they are worth so little, and cost so much to post -they are just not worth putting on ebay. I do usually take them to car shows - but no-one seems interested.....

[katy]

I’ve put lot’s of armatures in vices to loosen and/or tighten the end nut and never had a problem w/distortion. The trick is to put it horizontal in the vice and make sure that the vise jaws are squarely on 2 opposite pole pieces and not straddling a gap. Have also done lots of alternator armatures this way.