Before you reinstall a good camshaft, remove theminor surface defects on the cams and the camshaft byusing crocus cloth or a fine stone.INSPECTING, MAINTAINING, ANDREPLACING PISTON RINGS AND PISTONSThe following paragraphs are general proceduresfor inspections, maintenance, and replacement of pistonrings and pistons. You must consult the manufacturer’stechnical manual for specific instructions.PISTON RINGSOver a period of time all piston rings wear. Somestick and may even break. While you may be able to freestuck rings and make them serviceable, you mustreplace excessively worn or broken rings with new ones.The installation of a new set of rings in an enginerequires great care. Most of the damage that is doneoccurs when the rings are being placed in the groovesof a piston or when the piston is being inserted into thecylinder bore.Be very careful when you remove the piston andconnecting rod from the cylinder. In most engines, youshould not remove a piston from a cylinder until youhave scraped the cylinder surface above the ring travelarea. In addition to removing all carbon, you mustremove any appreciable ridge before removing thepiston. Do not remove a ridge by grinding, as this willallow small abrasive particles from the stone to enter theengine. Use a metal scraper and place a cloth in thecylinder to catch all metal cuttings. You can usuallyscrape enough from the lip of a cylinder to allow thepiston assembly to slide out of the liner. After removingthe piston, you can make a more detailed inspection ofthe ridge.Finish scraping the remaining ridge, but be carefulnot to go too deep. Finish the surface with a handstone.For large ridges, you may need to remove the liner anduse a small power grinder.With the piston and connecting rod removed, checkthe condition and wear of the piston pin bushing, bothin the piston and in the connecting rod.The best way to remove and install piston rings iswith a tool similar to that shown in figure 3-19. Thesetools generally have a device that limits the amount thering can be spread and prevents the rings from beingdeformed or broken.A ring that is securely stuck in the groove willrequire additional work. You may need to soak the pistonFigure 3-19.–Piston ring tools used for removal or installation.overnight in an approved cleaning solvent or in dieseloil. If soaking does not free the ring, you must drive itout with a brass drift. The end of the drift should beshaped and ground to permit its use without damage tothe lands.After removing the rings, thoroughly clean thepiston with special attention to the ring grooves. (Dieseloil or kerosene are satisfactory cleaning agents.) Inaddition, you may need to clean excessive deposits fromthe oil return holes in the bottom of the oil control ringgrooves with a twist drill of a diameter correspondingto the original size of the holes.Make another complete inspection after cleaningthe piston. Check all parts for any defects that couldrequire replacement of the piston. Give particularattention to the ring grooves, especially if the pistonshave been in service for a long period of time. A certainamount of enlargement of the width of the grooves isnormal, and SHOULDERING of the groove may occur.Shouldering, as illustrated in figure 3-20, results fromthe “hammering out” motion of the rings. The radialdepth of thickness of the ring is much less than thegroove depth, and while the ring wears away an amountof metal corresponding to its own width, the metal at thebottom of the groove remains unchanged. Shouldering3-14
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business