Inspection
1. Check the cylinder bores for taper, out-of-roundness, and scratches. Start at the top of the bores. If they are worn, a small ridge will be visible on the thrust side. This indicates the top of the piston ring stroke. Cylinder bore wear can be determined without disassembling the engine or removing the cylinder head. If there is excessive oil consumption, accompanied by blue smoke from the exhaust pipe, this is a sure sign of bore and piston ring wear.
2. Measure the bore diameter across the block, but just below the wear ridge. This can be done with an inside micrometer. Compare it to the diameter at the base of the cylinder bore, which is not subject to wear. If measuring instruments are not available, use a piston without rings, and measure the clearance between the piston and the cylinder wall with a feeler gauge. See: Specifications. If the cylinder wear exceeds the permissible limits, the cylinder bores must be bored, but note the following points:
- a) Pistons and cylinder bores are closely matched during manufacture. The actual piston diameter is indicated by the number at the top; the same number is printed on the crankcase and indicates the diameter.
- b) After boring, the cylinder bores must be accurately measured and oversized pistons selected from those available to provide the piston to cylinder wall clearance specified in the Specifications.
- c) The piston diameter is measured across the base of the skirt.
3. If there is marginal wear within the tolerance, you can simply install new special piston rings.
4. Carefully inspect the crankcase and cylinder block for cracks and damage, use a piece of wire to check all lubrication channels and cooling channels to ensure they are not clogged.
5. Note that the rubber plug located next to the clutch housing flange on the cylinder block covers the hole for installing the TDC diagnostic sensor. The sensor is connected to the diagnostic unit and indicates TDC from the position of the pin group in the crankshaft counterweight.
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