Dismantling Marchal and Paris Rhone Dynamos


How do I get the pulley off the dynamo?
N.B. You really only need to do this if you are swapping pulleys between dynamos or need access to the front bearing. Brushes can be inspected / changed without removing the pulley and front plate.

The nut has a standard thread i.e. undoes in an anti-clockwise direction as you face the dynamo. It is done up to a high torque but a compressed air impact gun undoes the nut easily as long as you can hold the pulley firmly enough to prevent it turning  without damaging it. For difficult cases make use of the two threaded holes as shown opposite (they are M8 thread). The outer pair of bolts are just packing.

If the pulley has recently been removed it will slide off the shaft once the nut and washer have been removed. The chances are though that it will be stuck solid and you will need to use the method shown below.

 
     
  Thread two M8 bolts into the holes in the pulley until they meet the end plate. Tighten each a a bit in turn and they will slowly move the pulley forward off the shaft. Once the mating surfaces of the pulley and shaft have been cleaned and greased the pulley will simply slide on and off the shaft.

The woodruff (half moon) key may stay in the shaft when the pulley is removed or may need tapping out but be careful not to loose it!

On a Marchal dynamo the endplate is in two parts and includes a bearing cover secured by six recessed bolts with allen key heads. To remove the whole plate is a matter of undoing the six bolts round the outside, then using two of these bolts in the threaded holes to act as a 'puller'. The procedure is the same as shown below for the rear cover plate.


How do I get to the brushes?

To examine or change the brushes the rear endplate must be removed. Note the use of a piece of copper tube to protect the electrical socket)

Once the six retaining bolts have been removed two of them are used in the spare threaded holes as shown to pull the end plate out. It is a tight fit due to the rubber seal (clearly visible in the photo far right). On a Paris Rhone dynamo there are no threaded holes for this but the end plate protrudes beyond the main casing and can be tapped off a bit at a time working round the circumference.


Brushes on a Marchal type dynamo

  The end plate cannot be completely removed until two of the electrical screws that connect the brush assembly to cables from the main body are undone. These also secure the wires from two of the brushes so make a careful note of where everything goes! The Marchal dynamo has four brushes with bevelled ends as they are mounted off-centre. Click the image to enlarge / Cliquez pour agrandir l'image

The Marchal type dynamo I have dismantled for the photos is from a rebuilt engine unused apart from the factory running in process to achieve the final 'fiche de rodage' certificate. I am about to send the brushes away to have a duplicate set made. Having done so and assuming the quality is ok the company will then be able to produce sets of brushes for M201 owners. Watch this space.

The Paris Rhone dynamo has a different brush assembly and brushes. I intend to dismantle one in the next few days to both photograph and to send the brushes away to get a duplicate set made. So again, watch this space.

Reassembly

Before reassembling, clean and grease the rubber dust / water seal. Having four brushes, the Marchal type dynamo is quite tricky to reassemble and I don't recommend attempting this when you are tired / not in a good mood. Basically,  pushing back all four brushes to allow them onto the commutator and keeping everything in place while you reconnect the wires that connect to two of them (if you have disconnected these)  is all but impossible unless you make up four pins to hold the brushes back until reassembly is almost complete (see photo opposite).

The pins I used were made from coat hanger wire and worked well but with the benefit of hindsight it would have been better to have completed the loop at the end of each and tied a piece of thread to each to make removal easier. With the pins in place to hold the brushes back it is possible to reconnect the wires to two of the brushes. Getting the tags on the wires to line up with the threaded hole on the brush assembly so that the screw can be inserted is a challenge that can be made easier by using a nail to line them all up. A finger and thumb can then be used to pinch them together in place before removing the nail and inserting the screw. (see photo below)

Once the wires have been reconnected to two of the brush assemblies the end plate can be eased towards the body checking that the brushes do not catch on the commutator.

With the brushes in place over the commutator and a small gap left between the end plate and the body, remove each of the pins allowing the brushes to make contact with the commutator. Make sure the bolt holes line up before tapping the endplate in working round the edge to keep it square. When it is home far enough the bolts can be inserted and used to finish the task but again they need tightening equally working round the edge to move the plate in squarely and a bit at a time.

The dynamo worked fine after its dismantling ordeal though having four brushes certainly made the reassembly more challenging. With only two brushes the Paris Rhone dynamo is rather easier to dismantle and reassemble to inspect the brushes.