PISTONS - TM-5-3805-260-24

TM-5-3805-260-24 Scraper Tractor: Elevating Self-Propelled 11 Cubic Yard Sectionalized and Nonsectionalized Manual
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TM 5-3805-260-24 PISTONS Check pistons for scores, cracks or enlarged ring grooves; replace pistons if any of these conditions are found. Measure each piston with a micrometer in relation to the cylinder bore diameter to be sure the clearance is between 0. 002 in. minimum and 0. 004 in. maximum. Check fit of wrist pins on pistons and connecting rod bushings. Wrist pin should be a light press fit in pistons. If wrist pin is loose fit, the pin, piston, or both should be replaced. Check fit of wrist pin in connecting rod bushing by rocking the piston. This clearance should not exceed 0. 0015 in. Replace wrist pin bushings if excessive clearance is found. Wrist pin bushings should be reamed after being pressed into connecting rods. Replace Teflon plugs in each end of the wrist pins. PISTON RINGS Check fit of piston rings in piston ring grooves. Check ring gap with rings installed in cylinder bores. PISTON RING POSITIONS - GAPS AND GROOVE CLEARANCE All rings must be located in their proper ring grooves as shown. The rings can be identified by the width and should be installed with the bevel or the pipmark (if any) toward the top of the piston. This applies to Cast Iron Pistons (only as shown above). 3-20 CRANKSHAFT Check crankshaft screw threads, keyways, tapered ends and all machined and ground surfaces for wear, scores, or damage. Crankshaft journals which are out of round more than 0. 001 in. must be reground. Bearing inserts are avail- able in 0. 010 in. , 0. 020 in. , and 0. 030 in. undersizes for reground crankshafts. Main bearing journals must be maintained so bearings are snug fit. Check to be sure the oil passages are open and clean through the crankshaft. CONNECTING ROD BEARINGS Check connecting rod bearings on crankshaft journals for proper fit. Used bearing inserts should be replaced. Connecting rod caps are not interchangeable. The locking slots of the connecting rod and cap should be positioned adjacent to each other. Clearance between the connecting rod journal and the connecting rod bearing must not be less than 0. 0003 in. Or more than 0. 0021 in. after rebuilding. MAIN BEARINGS Check for wear or flat spots; if found, bearings should be replaced. The sleeve bearing should be checked for scores and wear and replaced if necessary. UNLOADER MECHANISM Used unloader mechanism should be replaced by unloader kit 265014. The new unloader pistons should be a loose sliding fit in the unloader piston bores of the cylinder block.

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