ZS Starter

The three screws securing the solenoid to the motor assembly. They are Torx 25, but with a very shallow recess. I was only able to remove one with an air-gun, the others had to be drilled out.

From left to right: piston, casing with windings, contact bar and insulated end-plate carrying the three contacts.

The end of the casing was peened over a flange on the insulated end-plate, so dismantling is destructive. The one contact is heavily burnt, the other completely clean, and signs that contact is being made in just three small areas. This indicates that one contact has always closed last and opened first, whereas ordinarily one would expect it to be chance as to which contact closed last/opened first on any one operation. Perhaps this means the contact bar is canted over somewhat.

The contact bar, similar burning on just one side.

Spring 'A' pushes the piston back which disengages the pinion from the flywheel. Spring 'C' pushes the contact bar away from the contacts to cut power to the motor. Spring 'B' is the interesting one. When powered the solenoid winding pulls the piston down hard to the bottom of the recess, and the piston pushes against the white part of the contact bar assembly. That pushes the contact bar itself against the contacts, and any excess travel of the solenoid piston and the white part is absorbed by spring 'B'. So it is effectively only spring 'B' - the lightest spring - that is pressing the contact bar against the contacts. By contrast the V8 starter has a significantly heavier spring that pushes the bar down onto the contacts, and there is no sign of burning on those after 14 years of use.