PISTONS AND CONNECTING RODS—F.23.Check the fitted gap of the compression andscraper rings. In worn cylinders the gap should bechecked at the bottom of the cylinder. For detailsof ring gap dimensions (see Technical Data).4.Check the fit of the gudgeon pin in the piston boreand in the small end bush of the connecting rod.The pin is a transition fit in the piston, i.e. within thelimits of —0.00015 in (0.004 mm) to +0.00025 in(0,006 mm). The clearance dimension betweenthe gudgeon pin and the small end bush of theconnecting rod is between 0.00075 in (0.01q mm)and 0.0017 in (0,04.3 mm). For details of pistonbore, gudgeon pin and small end bush borediameters see Technical Data. To renew the smallend hush, press out the old bush using a suitabletool. Remove any sharp edges around the smallend parent bore. Press in the new bush, ensuringthat the oil hole in the hush coincides with the holein the connecting rod. Ream out theFig. F.3.Exploded view of Piston and Connecting RodAssembly.Fig. F.4.Numbering of Connecting Rods and Caps.new bush to suit the gudgeon pin and check theconnecting rod for parallelism (see Technical Data).5.Examine the big end bearing shells for wear andscoring. Also examine the crankpins and ifnecessary, remove the crankshaft, regrind thecrankpins and fit undersize bearing shells. Theseare available in undersizes of 0.010 in (0,25 mm),0.020 in (0,51 mm) and 0.030 in (0,76 mm). Fordetails of crankshaft removal see Page H.31.6.If the engine has been in service for a lengthyperiod, it is advisable to fit new piston circlips evenif the old ones do not appear to be strained ordamaged.
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