BMW (1983-89) M635CSI

WHAT TO LOOK FOR CORROSION CONCERNS

Rust is a big enemy of the 6 Series, and signs of corrosion in rear wheelarches, sills and door bottoms are likely to only be the tip of the iceberg, with worse lurking beneath. Front wings need particular scrutiny – around the indicators and the lower rear section ahead of the sills – while inner wing seams can rot around the battery tray. Watch for problems caused by water leaking into the boot, along with rot around the fuel tank, sunroof aperture jacking points and floors.

ENGINE AND GEARBOX

The M88 engine requires fastidious maintenance because a rebuild is far from cheap, while timing chain replacement at 100,000 miles is an absolute priority. It can be inspected by removing the rocker cover, but there’s often no warning of failure – budget around £3500 to change it, but it will cost more than twice that if it lets go. Check for crunchy shifts from the dog-leg Getrag gearbox, a heavy clutch and untoward noises from the ZF limited-slip differential.

STRONG STOPPERS?

Weight and performance take their toll on the brakes. The high-pressure system needs annual fluid changes, while a hard pedal points to a failed accumulator. Perished suspension bushes and corrosion around rear subframe mountings are potential trouble-spots. The M635 is a serious performance machine, so if either the brakes or suspension appear to have been neglected then it raises questions over where else a previous owner has penny-pinched.