Hi Torque Starter Motor
The hi-torque starter is a direct replacement for the original MGA inertia starter motor. Expect to pay between £160 to £180. One significant advantage is that it engages the flywheel teeth from the opposite side and so can be used on an otherwise worn ring gear.
Wiring the motor is straight forward, albeit slightly different to the original. The existing heavy duty starter cable is attached to the bottom left post in the second picture and to the same terminal post as the main battery cable on the original starter switch. The starter is therefore always 'live'. A second 5 amp cable is attached to the spade terminal (just above the main power cable post in the photo) with the other end attached to the now vacant second terminal post on the starter switch. When the starter switch is pulled contact is made to the inbuilt solenoid. This causes the starter dog to slide forward and engage the ring gear. Only when the dog has engaged is the main power circuit completed to spin the powerful and geared spindle.
An additional benefit of this system is that the starter switch now only has to cope with a small current and should therefore last much longer.