Timing gear and top-end noise

Classic and Sports Car's buyer's guide lists three things to listen for on an E-Type: rattly timing gear, tapping from worn camshafts, and knocking from a worn bottom end. They sit at different ends of the expense scale, and learning to tell them apart is worth more than most inspections.

The rattle

Timing gear noise is a rattle or light clatter from the front of the engine, often most obvious at idle or on the overrun. Chains stretch, guides wear and tensioners lose their effect, and the result is slack that the engine announces. It is rarely a walk-away fault on its own, but it is a job that wants doing, and it is worth asking when it was last attended to.

The tap

A rhythmic tapping from the top of the engine points at the valve gear. Worn camshafts and their followers tap, and the XK's valve clearances are set by shims rather than by a quick adjustment, so even a correct clearance job is a measured, unhurried task. A tap that disappears as the engine warms may be clearances; a tap that stays is more likely wear.

The knock

A deep knock from low in the engine, especially one that gets worse as the engine warms and the oil thins, is the bottom end: main or big-end bearings. This is the serious one. It means a strip-down rather than an adjustment, and on a buying inspection it is the sound that ends the conversation or reprices the car.

Order of seriousness

Rattle, tap, knock: broadly in that order of cost and urgency. None of them is a reason to buy blind, and all three deserve to be identified rather than hoped away.