BURNED VALVES.

Sun (Auckland), Volume I, Issue 154, 20 September 1927, Page 6

BURNED VALVES.

PETROL NOT THE CAUSE. MECHANICAL FAULTS. Burnt exhaust valves—a problem with motor engineers since the invention of the petrol engine—lately have been a subject of interest in the motor trade following claims that the use of certain grades or brands of motor spirit must result in burnt valves. Motorists mostly are fair-minded people, and tne problem of selecting the fuel most suitable to the engines of the cars they operate can never be solved if it is approached with an unconscious or other bias against certain fuels.

Burnt valves are solely traceable to mechanical faults—chiefly the setting of the valve clearances, though the setting of the carburetter can accelerate “burning” as can the wrongful use of extra air.

A motorist troubled by burut exhaust valves can face the problem with the definite assurance that no spirit, whether imported or Australian made, will burn a‘properly adjusted valve. A second assurance is that a valve which is seating properly cannot burn The most frequent cause of faulty seating, however, is insufficient tappet clearance. This is found most often to he a fault with new engines, or engines newly assembled after an overhaul.

In both cases it is caused bv the clearances being set at a too small gap when the engine is cold. The result is that when the engine warms up the clearances are eliminated and the valves are not able to close down on to their seats.

A definite burning of the valves results, and a rapid carbon pitting of th* valve faces and valve seatings also occurs.

The remedy’ is very obvious, but it should be equally obvious that if overrent valve operation is obtained by an insistence on too small valve clearances the valve burning troubles will recur.