Engine lubricants have been found to both increase and reduce valve and seat wear,
depending on the additive composition and the amount of oil that reaches the valve/seat interface.
In inlet valves, liquid film lubrication is most dominant as temperatures are not usually high enough to volatilize the lubricant hydrocarbons and additives. Exhaust valves, however, are predominantly lubricated by solid films formed at the higher operating temperatures by oil additive ash compounds such as alkaline-earth and other metal oxides, sulphates, and phosphates (e.g. calcium, barium, magnesium, sodium, zinc, and molybdenum). Very thin metal oxide films have been found to be beneficial in reducing
valve wear [21]. Too much solid film lubricant, however, can be detrimental and lead to valve guttering or torching due to flaking (as described in Sections 3.3 and 3.4).
E N G I N E E R I N G R E S E A R C H S E R I E S
Automotive Engine Valve Recession
R Lewis and R S Dwyer-Joyce
Series Editor
Duncan Dowson
Professional Engineering Publishing Limited,
London and Bury St Edmunds, UK
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