1977 Triumph Stag 3.0L Petrol · DEC 740S

The bespoke 3.0-litre Triumph V8 suffered notorious overheating due to a high-mounted water pump that easily air-locked if coolant dropped, narrow engine water passages, and casting sand left in blocks from the factory. Furthermore, cylinder head studs entered the block at two opposing angles, producing lateral stress when hot that readily warped the aluminium heads and breached head gaskets.

The Triumph 3.0-litre V8 uses long single-row duplex chains to drive each overhead camshaft from a jackshaft. The timing chains stretch with use, and hydraulic tensioners wear or fail when oil changes are neglected or oil pressure drops. A stretched chain causes severe valve timing deviation, can jump teeth on sprockets, or snap completely, causing catastrophic piston-to-valve collision in the interference engine.

Constructed from untreated 1970s British Leyland steel with complex multi-box sections, the Stag body is highly prone to structural tinworm. Water leaks through weathered targa and windscreen seals soak into cabin carpets, rotting out inner and outer sills, floorpans and the crucial A-pillars behind front trim panels. Corroded sills cause the open body tub to flex and sag, misaligning doors and weakening the roll hoop structure.