PISTON SLAP

Rotorua Morning Post, Volume 1, Issue 152, 19 February 1932, Page 7

PISTON SLAP

A FREQUENT PROBLEM.

One of the problems that most frequently trouble motorists is that if an engine produees a tapping noise when it is cold, due to piston slap, does this indicate excessive wear in the cylinders ? The answer is that only a slight elearance is needed between the piston and cylinder to produce an audible tapping in a cold engine, and consequently no notice need be talcen of this. When the piston is rising on" the compression stroke the angle at which it is pushed upwards hy the oblique connecting rod is such as to force it sideways against the cylinder walls. An instant later it is driven downwards hy the burlit gases, and as the angle of the connecting rods is hy then reversed the side thrust becomes reversed also. Consequently, there is a tendency to "throw" the piston across from one side of the cylinder to the other, and a elearance of even l-1000ths of an inch in an engine of medium size will be sufficient to cause tapping. No anxiety need be felt on tbis score, and "tapping" may continue for a long, time before a big increase in the oil consumption sbows that reboring is required. To prevent rapid cylinder wear a cold engine should always he allowed to run for a short time before being called npon to propel the car. rhis allows the oil to cireulate and be thrown up from the big ends on to fche cylinder walls. New types of 'piston rings have rejently been developed which tend to lold the piston centrally in the cylinler hore so as to prevent slap occurung.