Distributors and HT leads are the components that control spark timing and deliver the high-voltage ignition pulse to each spark plug in the correct firing order. Two Lucas distributor types were fitted: the 25D4 (side-entry cap) on 1275cc engines and the 45D4 (top-entry cap) on 1500cc engines.
Distributors & HT Leads Specification
New and reconditioned distributors are available for both types. A reconditioned distributor has been fully stripped, inspected, and rebuilt with new bearings, shaft bushes, contact plate, and advance mechanism components. The vacuum advance unit (which advances the timing under light-load cruising conditions to improve fuel economy) and the centrifugal advance mechanism (which advances timing as engine speed rises) are both checked and calibrated to specification.
Distributors & HT Leads Maintenance
HT lead sets are available in standard carbon-core and silicone specification. Standard leads are adequate for an unmodified engine. Silicone leads provide superior insulation against spark leakage in damp conditions, better heat resistance in the high-temperature environment near the exhaust manifold, and longer service life. The leads connect from the distributor cap to each spark plug via the correct firing order.
Service Notes
Distributor caps and rotor arms are service items that should be renewed at the intervals specified in the workshop manual. A cracked cap allows moisture ingress that causes misfiring in damp conditions, a common complaint on Midgets driven in the British climate. Carbon brush connectors inside the cap transfer the spark from the rotor arm to each HT lead terminal.