Figure 3-22.–Checking ring gap clearance.been installed, check the ring-to-land clearance. (Seefig. 3-23.) If the clearance is too small, the ring maybind or seize, allowing improper sealing and blowby tooccur. If the clearance is excessive, the ring may flutterand break itself or the piston land.After you have properly installed all the rings, coatthe entire assembly with oil, then insert it into thecylinder bore. Position the rings so the gap of eachsuccessive ring is on an alternate side and the gaps arein line with the piston pin bosses. On large engines, usea chain fall to hold the piston assembly in position asyou lower it into the cylinder. (See fig. 3-24.)Figure 3-23.–Checking ring groove side clearance.75.56Figure 3-24.–Installing a piston in a cylinder bore with afunnel-type ring compressor.When a piston is being inserted into a cylinder, thepiston rings must be compressed evenly. Specialfunnel-type tools, similar to the one shown in figure 3-24are usually provided for this purpose. Another type ofring compressing tool is a steel band that can be placedaround the ring and tightened.PISTONSTrunk-type pistons are subject to forces such as gaspressure, side thrust, inertia, and friction. These forces,together with overheating and the presence of foreignmatter, may cause troubles such as undue piston wear,crown and land dragging, cracks, piston seizure,clogged oil holes, and piston pin bushing wear.Excessive Piston-to-Liner ClearanceSymptoms of excessive clearance between a pistonand its cylinder are piston slap and excessive oilconsumption. Piston slap occurs just after top deadcenter and bottom dead center, as the piston shifts itsthrust from one side to the other. As the cylinder taperincreases with wear, oil consumption increases. Sincetaper causes the rings to flex on each stroke of the piston,excess ring wear occurs, allowing lube oil to pass and3-16
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