My exhaust valve has been burned
QMy Land Rover Series II’S 2.25 petrol engine has burned an exhaust valve. Why might this be and what can I do? Stephen O’connor, Dublin
Martin says:
AExhaust valves typically burn because they have overheated. This may be directly caused by a weak mixture (incorrectly adjusted carburettor or insufficient fuel supply) or over-advanced ignition timing.
Indirectly it may be caused by too-small valve clearances: the valves conduct much of their heat away via the valve seats while closed. If the valve seats are cut directly into cast-iron as on your engine, then they gradually erode when used with unleaded petrol. This creates a poor heat-conducting interface between valve and seat and also decreases the valve clearance as the seat erodes, compounding the problem. We’d advise you to have new valves fitted throughout and hardened seats installed, plus new valve guides if necessary. It should be a one-off job, but do check the mixture and timing to prevent a repeat – and keep an eye on the valve clearances, which will close up as the new gasket compresses.
You should certainly reset them after retorquing the head bolts following the initial engine run-up, as recommended by the Land Rover workshop manual.