Morris Minor Owners Club

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.

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........

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?

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.....

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

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

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

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

Ditto

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!

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

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.....

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.