NEW PISTON RINGS

Hawera Star, Volume LI, 3 January 1931, Page 12

NEW PISTON RINGS

There is unfortunately a belief in many quarters that whenever a cylinder is losing compression or there are signs of piston slap, a new set of rings will soon put matters right. Actually, if the new rings are ill chosen or badly fitted that may make the last stage of the cylinder worse than the first. To understand the position clearly the motorist must picture to himself that each piston ring is to all intents a perfect -circle which makes uniform and close contact with the walls of the cylinder. If the cylinder wears regularly—that is to say, retains perfect circular form, but merely through wear and tear has its diameter enlarged by a few thousandths of an inch —then new rings may effect a cure, but whenever the cylinder has worn seriously it will almost certain have, taken on an elliptical shape, and so until it is lapped, honed, or rebored again to a cylindrical form it is futile to try and force in new rings and pistons, since a perfect circle cannot make a gastight joint with the elliptical contour of a worn cylinder. The fitting of new piston rings is not a job to be undertaken by the amateur, and it is very often necessary for some lathe work to be carried out on the pistons themselves in order to true up and re-face the piston grooves. Similarly, where the cylinder wear is so serious as to call for treatment, the engine must, of course, be entrusted to some pro-perly-equipped machine shop.