Check prior to cylinder head removal
1. Oil tank overfilled.
2. Oil carryover.
3. Breather hose restricted.
4. Restricted oil filter.
Check after cylinder head removal
1. Oil return passages for clogging.
2. Valve guide seals.
3. Valve guide to valve stem clearance.
4. Gasket surface of both head and cylinder.
5. Cylinder head casting's porosity allowing oil to drain into combustion chamber.
6. O-ring damaged or missing from oil pump/crankcase junction.
Adjustment and testing
Often only cylinder head and cylinder repair is needed (valves, rings, piston, etc.). Service these components with the engine in the frame. See 3.13 TOP END OVERHAUL: DISASSEMBLY, Stripping Motorcycle for Top End Repair.
After disassembling the top end only, it may be found that crankcase repair is necessary. Crankcase repair requires removal of engine crankcase from chassis. See 3.10 REMOVING ENGINE FROM CHASSIS.
Note. Do not lay engine on primary side. Laying engine on primary side will damage the clutch cable end fitting. If fitting is damaged, replace the clutch cable.
Symptoms indicating a need for engine repair are often misleading. If more than one symptom is present, possible causes can be narrowed down to make a partial diagnosis. An above normal consumption of oil, for example, could be caused by several mechanical faults. However, when accompanied by blue-gray exhaust smoke and low engine compression, it indicates worn piston rings. Low compression by itself however, may indicate leaking valves, in addition to worn piston rings. See 1.28 TROUBLESHOOTING.
Piston slap is a condition where piston and/or cylinder are worn out-of-round and are loose fitting, allowing the piston to slap from front to rear of the cylinder as it moves up and down.
Frequently, valves, rings, pins, bushings and bearings need attention at the same time. If any one of the above components is worn, inspect all of these components. Repair or replace as necessary.