Welcome to our Site for MG, Triumph and Austin-Healey Car Information.


MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - MGA Dynamo

Hi I recently returned home and switched the ignition off, engine duly stopped but ignition light stayed on.
Looked under the bonnet and the dynamo was running as an electric motor !
Why is this, does it mean a new dynamo ? has this happened to any other MGA owners ?
DJ Joy

Your fan belt must have been loose to allow it to turn, but if it hadn't been able to turn it may have burnt out! How did you stop it? If my memory serves me correctly this is caused by the cut-out contacts (in the regulator unit) being stuck or welded together. Separating the contacts and cleaning them with emery paper could solve the problem. The regulator unit could probably do with servicing, the instructions for doing this are in the workshop manual and fairly simple.
Lindsay Sampford

Lindsay is correct - the cut out relay in the control unit (regulator) is stuck closed. And yes, the fan belt is loose, but you want it to be quite loose - Nearly a full inch of deflection between the dynamo and water pump pulleys when pressed in the middle. A tight belt will cause premature wear on the rear bushing of the dynamo. Cheers - Dave
D W DuBois

The MGB WSM (or dynamo-equipped cars) says half an inch in the middle of the longest run, which is between the dynamo and crank pulley.
Dave O'Neill 2

Dave O. - That would be the absolute tightest that I would allow it to run on our early MGB. With the smaller cross section belt, there is not as much tension as on the T series cars that used a buss/truck belt that was nearly twice the cross section of the standard auto belt. Those were so stiff that, unless the belt was segmented, they would still cause excessive wear on the generator bushing when set at 1/2 inch. Cheers - Dave D.
D W DuBois


Isn't the MGA fanbelt the same as the MGB?
Dave O'Neill 2

Dave O. "Isn't the MGA fanbelt the same as the MGB?" Yes it is. I guess that I should have stated that the MGA belt is the same as the MGB belt. I was just rambling on as to how I cam up with the 1 inch measurement. Cheers - Dave D.
D W DuBois

Thanks Guys, so strip down the regulator ps I stopped it by disconnecting the battery.
DJ Joy

This thread was discussed between 27/11/2014 and 28/11/2014

MG MGA index

This thread is from the archives. Join the live MG MGA BBS now