lucas dynamos

They can be run the other way but you have to flash a twelve volt supply across them to reverse the magnetism, I cant remember much detail but somebody will.

If it's new (or reconditioned) you just fit it and it will adopt the car's polarity. To change polarity, earth the casing and lightly brush the excitation terminal (the wee one) with a lead going to the other battery post. So to change from +ve to -ve, mount the dynamo and before connecting the big juicy wire, briefly make a connection between the

Ian

I don't see how. Dynamos have mechanical regulators and the battery volts aren't applied to the field windings with no charge of the correct polarity from the dynamo to pull in the cutout relay. This is deliberate to prevent damage due to wrong polarity connection of a battery. The initial output before the cutout operates is generated by residual magnetism in the field core. After that the battery/dynamo provides the field current.

That's to reverse the electrical polarity, not the rotation.

I don't know if they're rotatable backwards and it's such an obscure requirement that I have never needed to know. Certainly things like the pulley retaining nut would now be reverse-threaded and should have some loctite added. It's also possible that the brush springs and holders could object to reverse rotation.

Nuts between driveshaft and hub on the suspension sometimes are lefthand thread on the nearside, but not always. On a dynamo, the pulley is keyed to the shaft so the nut is only to keep the pulley secure.

Years ago I coupled up a lucas dynamo to an old SIF lawnmower engine using two vee pulleys and a belt. Problem was that it produced a very low output (even with the field energised from a 12volt supply).

After some head scratching and really looking at the dynamo casing it was marked with a 'direction' arrow.

Recobbling so that the engine drove the dynamo directly via a coupling, so that it rotated in the direction of the arrow (clockwise) all was well. I suspect that these dynamos could be modified to produce a useful output in the reverse direction by altering the 'timing' of the brushes.

Roj