Disassembly/Inspection and Service Remove Flywheel End Oil Seals Remove fl ywheel end crankshaft and camshaft oil seals from crankcase. Crankcase Inspection and Service NOTE: If bore is beyond wear limit, a new miniblock or short block will be required. Check all gasket surfaces to make sure they are free of gasket fragments. Gasket surfaces must also be free of deep scratches or nicks. Inspect main bearing (if equipped) for wear or damage. Replace crankcase using a mini-block or short block if required. Check cylinder bore for scoring. In severe cases, unburned fuel can cause scuffi ng and scoring of cylinder wall. It washes necessary lubricating oils off piston and cylinder wall.
As raw fuel seeps down cylinder wall, piston rings make metal to metal contact with wall. Scoring of cylinder wall can also be caused by localized hot spots resulting from a cooling system problem or from inadequate or contaminated lubrication. If cylinder bore is badly scored, excessively worn, tapered, or out-of-round, resizing is necessary. Use an inside micrometer to determine amount of wear, then select nearest suitable oversize of either 0.08 mm (0.003 in.), 0.25 mm (0.010 in.), or 0.50 mm (0.020 in.). Resizing to one of these oversizes will allow usage of available oversize piston and ring assemblies.
Initially, resize using a boring bar, then use following procedures for honing cylinder. Honing Detail 2. With lower edge of each stone positioned even with lowest edge of bore, start drill and honing process. Move hone up and down while resizing to prevent formation of cutting ridges. Check size frequently. 3. When bore is within 0.064 mm (0.0025 in.) of desired size, remove coarse stones and replace with burnishing stones. Continue with burnishing stones until within 0.013 mm (0.0005 in.) of desired size and then use fi nish stones (220-280 grit) and polish to fi nal size. A crosshatch should be observed if honing is done correctly.
Crosshatch should intersect at approximately 23-33° off horizontal. Too fl at an angle could cause rings to skip and wear excessively, too steep an angle will result in high oil consumption. 4. After resizing, check bore for roundness, taper, and size. Use an inside micrometer, telescoping gauge, or bore gauge to take measurements. These measurements should be taken at three locations in cylinder-at top, middle, and bottom. Two measurements should be taken (perpendicular to each other) at each three locations. Clean Cylinder Bore After Honing Proper cleaning of cylinder walls following boring and/ or honing is very critical to a successful overhaul.
Machining grit left in cylinder bore can destroy an engine in less than one hour of operation after a rebuild. Final cleaning operation should always be a thorough scrubbing with a brush and hot, soapy water. Use a strong detergent that is capable of breaking down machining oil while maintaining a good level of suds. If suds break down during cleaning, discard dirty water and start again with more hot water and detergent. Following scrubbing, rinse cylinder with very hot, clear water, dry it completely, and apply a light coating of engine oil to prevent rusting.
While most commercially available cylinder hones can be used with either portable drills or drill presses, use of a low speed drill press is preferred as it facilitates more accurate alignment of bore in relation to crankshaft crossbore. Honing is best accomplished at a drill speed of about 250 RPM and 60 strokes per minute. After installing coarse stones in hone, proceed as follows: 1. Lower hone into bore and after centering, adjust so that stones are in contact with cylinder wall. Use of a commercial cutting-cooling agent is recommended. 66 690 01 Rev. C KohlerEngines.com 57 A A 23°-33° Crosshatch