Sometimes, the pistons will apparently be frozen in the cylinders, particularly in very cold weather and when fairly thick oil is used. This is but a temporary trouble and can be cured by pouring in a thin oil or, better yet, kerosene. The thin oil will work more quickly if heated, and should be poured in on top of the pistons, either through the petcock, valve-cap opening, or other available opening in the top of the cylinder. Being thin - and if hot, thinner than usual - the oil will work down between piston and cylinder walls, cutting through the thicker oil which has hardened there under the influence of the cold weather, and thus will free the pistons.
Many times the pistons will wear just enough so that they are loose in the cylinder all the way around. This causes leakage of gas, piston slaps, and other similar troubles. If the owner of the car does not care to buy new pistons, or if the car is an "orphan", or if, for other reasons, pistons cannot be obtained, the clever repair man can remedy the trouble at small expense. The process consists in heating and expanding the old pistons. The heating is done in charcoal and must be done very carefully and slowly. After the pistons become red hot the fire is allowed to go out slowly, so that the piston is cooled in its charcoal bed. Sometimes as much as 4/1000 of an inch can be gained in this way. When the pistons are so far gone that they cannot be handled in this way, they must be replaced with new ones.
When the cylinders have worn so as to require grinding out, or when scoring necessitates this, oversize pistons must be used. In the majority of factories having any kind of system, three oversizes are made 4/1000 inch over, 5/1000 -inch over, and 11/1000 -inch over. The first provides for the initial grinding-out of the cylinder, the second for the second grinding, and the third for a lighter, final grinding. Beyond this, it is considered, the cylinder will be too thin to warrant further grinding; moreover, by the time three cylinder grindings have been lived out, the balance of the car will doubtless be too far gone to justify further cylinder repair work. Many factories, particularly those making a very light-weight car where thicknesses everywhere are kept down to the limit, allow but two oversizes, and thus, two grindings.