The motor is tubbier than that used for the A3 and A4 engines, but is very similar in appearance. Check the brushes - here they are almost new. Clean off any hair, thread and muck from the outside. Carefully clean the commutator. Chew the end of a matchstick. No, the other end ! Make it flat and then trim off the sides to give a narrow wooden brush. Use this to clean off the surface muck as you gently rotate the spindle.

Add a minute drop of light oil to each end of the spindle, where it passes through a brass bush. The bush has a slight recess. If the oil forms a blob here, then it is too thick and there is too much of it. Apply a drop from the end of a pin or very fine screwdriver. Capilliary action will draw the oil into the bush where it is needed.

The motor fits vertically from above. Here is a view from underneath, with the work gear coming out of the baseplate towards you. The tiny countersunk screws hold the motor in place. Make sure that these are holding the motor firmly. This engine seems to have reports of working well in one direction, but not the other. a loose motor is a possible cause.

The motor in place from above. The capacitor and choke coil are soldered on, and best left that way unless you intend to replace the motor. Be carefull of the copper pickup strips.

Seat the red plastic insulation block, and fit the retaining screw. This screw provides the connection from the chassis to the motor. If left loose, or missed off, the electrical continuity will be intermittent at best. The screw also clamps the connection between the pickup tabs and the motor. If you haven't already done so, clean the ends of the pickups and make sure that they are shiny.