“OIL-PUMPING”

Timaru Herald, Volume CXXV, Issue 18536, 5 April 1930, Page 15 (Supplement)

“OIL-PUMPING”

TROUBLE AFTER LONG SERVICE. One of the principal troubles which may be experienced with an engine that has undergone lengthy service is what is known as “oil pumping.” The indication of this trouble is continual fouling of the sparking plugs, a great amount of blue smoke coming from the exhaust and rapid formation of carbon of a wet and stick nature. Although some of the causes of this trouble are relative to piston condition, care should be taken to check over the lubrication adjustment to ensure that an excessive amount is not being given to the engine. If the adjustment is all right, then perhaps the piston is cocked in the cylinder—caused by a twist or bend in the connecting rod. In such a case the edge of the piston pushes the oil up into the combustion chamber. If a piston which is cocked is allowed to function indefinitely, undue pressure will be exerted upon the cylinder and piston walls, with quick and uneven wear, which can only be cured by regrinding or reboring. It will also cause piston slap and loss of compression and power. Rings which do not fit the ring grooves or cylinder walls correctly are conducive to the trouble of “oil pumping,” as are also worn pistons. There are two methods of overcoming excessive lubrication by working on the pistons, i.e., by drilling holes round the piston skirt, and by cutting a groove. The drilling of holes in the piston provides an outlet for excess oil. By the second method, a deep groove may be turned in the bottom of the piston skirt, something similar to a piston ring groove, but with the lower edge bevelled off. When this is done a series of about eight small holes are drilled at the angle into the inside of the piston from the bottom of the groove. The groove acts as a scraper, and removes the excess oil from the cylinder walls into the groove, whence it passes through the holes to the interior of the piston and so drops back into the crank case.