Page:Popular Science Monthly Volume 88.djvu/161

 Pttteti Sedt

��Popular Science Monthy

if the work is properly carried on but if- for any reason the piston should be pushed too far up into the cylinder on some types of engines the top ring will expand into the combustion chamber and will lock the pistons tightly in place. This is a difficult condition to overcome with some forms of cylinders though if the cylinder casting is of the L or T form it may be possible to compress the rings sufficiently to remove the piston by sim- ple means. The best method is shown at Fig. 13, A. A very thin strip of metal of approximately the same width as the piston rings is passed through one of the valve chamber openings and passed around the pis- ton and pulled out through the other opening. It requires the services of two people and sometimes three to remove a pis- ton stuck in this man- ner. The efforts of one are directed to keep the band taut un- der the ring and to exert an upward pull which forces that por- tion of the ring em- braced by the metal band to fill the groove in the piston. Another person uses a pair of screw drivers, one through each valve chamber opening to compress the ring at the points indi- cated in the drawing. This means that a three-point compressional effect is ob- tained and it is a simple matter for the third person to draw the piston back into the cylinder when the ring has been properly compressed in its groove. It is not always possible to compress the ring so the only other alternative is to break it in a number of pieces by hitting the brittle ring with a drift or chisel and then withdrawing the pieces one at a time until the ring has been entirely re- moved. With the T-head cylinder it is sometimes possible to remove the ring without the use of the metal bands, as that member is compressed at diamet- rically opposite points by a screw driver

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inserted through each valve chamber cap.

Fitting Piston Rings Before installing new rings, they should be carefully fitted to the grooves to which they are applied. The tools required are a large piece of fine emery cloth, a thin, flat file, a small vise with copper or leaden jaw clips, and a smooth hard surface such as that afforded by the top of a surface plate or a well- planed piece of hard wood. After mak- ing sure that all deposits of burnt oil and carbon have been removed from the piston grooves, three rings are selected, one for each groove. The ring is turned

���Fig. II. Forms of valve grinding tools and methods of grinding

all around its circumference into the groove it is to fit, which can be done without springing it over the piston as the outside edge of the ring may be used to test the width of the groove just as well as the inside edge. The ring should be a fair fit and while free to move cir- cumferentially there should be no ap- preciable up and down motion.

The ring should be pushed into the cyl- inder at least two inches up from the bottom and endeavor should be made to have the lower edge of the ring parallel with the bottom of the cylinder. If the ring is not of correct diameter, but is sliglitly larger than the cylinder bore, this condition will be evident by the angular slots of the rings being out of line or by difficulty in inserting the ring if it is a

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