CYLINDER WEAR.

Auckland Star, Volume LXVIII, Issue 69, 23 March 1937, Page 18

CYLINDER WEAR.

LUBRICATION AND RINGS. I BRITISH EXPERT'S OPINION. - I Among interesting subjects discussed recently with "The Motor," London, by Mr. A. Taub, a leading engine designer, was cylinder wear, his opinions regarding which are based upon the results of a great deal of research both in England and America. He regards adequate lubrication as the best possible antidote as this will constantly replenish the oil film on the cylinder bore and will help to wash away acidic products of combustion which causes corrosion.

Provided that the oil employed retains sufficient viscosity at the fairly high temperatures reached under high-speed running conditions, it should be as thin as is practicable at low temperatures so as to reach the cylinders as soon as possible after a cold start. Thermostatic control of 'water circulation is obviously of assistance in accelerating the warming-up process. As a result of analysing the rate of wear in a large number of American engines of widely varying sizes and types, it was found that the one which showed the least wear, and, incidentally, the lowest oil consumption was notable for the use of splash lubrication. The greatest rate of wear occurred in the engine in which the escape or oil from the big-ends was at a minimum.

Working on this basis, Mr. Taub naturally regards piston ring design as a most vital factor; copious lubrication is not a practical solution to the wear problem unless the oil can be controlled. Furthermore, efficient rings will prevent the gases from blowing past the piston in quantities and this "blow-by" is destructive of the oil film and the surfaces of the bore and rings.

By measuring the volume of gas blowing past the piston at various speeds. it was found that this might amount to half a cubic foot per minute up to a certain critical limit, but that at higher speeds the "blowby" increased suddenly and rapidly. This led to the discovery that from the critical speed upwards the piston rings (.which, after all, are only circular springs) were subject to an intense vibration which has been called "ring flutter."

Vibrating rings cannot maintain proper contact with the bore, and the next step was to evolve a design which would not be so subject to this trouble. In brief, it was done by abandoning the principle of uniform radial pressure in favour of a ring in which the pressure varies in a pre-determined manner; it is greatest towards the gap and at a point exactly opposite to the gap. Mr. Taub has also given a great deal of consideration to other factors such as the finish of pistons and cylinders, the way in which the pistons *rock on the gudgeon pins, crankcase ventilation systems, different kinds of lubricant, and so forth. He says that to-day, by utilising all the latest methods, bore wear can be reduced to about fourthousandths of an inch in 2;1,000 miles of average running, a very satisfactory figure.