2.
Measure the cylinder bore with a cylinder gauge at the three levels indicated, in the directions A and B.
Check the cylinder block for scores, rust and corrosion. Also check for cracks or any other defects. Replace the block if defective.
Measure the cylinder bore with a cylinder gauge at the three levels indicated, in the directions A and B.
If the cylinder bores show more than the specified out-of-round or taper, or if the cylidner walls are badly scuffed or scored, the cylinder block should be rebored and honed. New oversize pistons and rings should be installed.
Standard value |
Cylinder bore : |
3.5 : 93 - 93.03 mm (3.661 - 3.6625 in.) |
3.0: 91.1 - 91.13 mm (3.587 - 3.588 in.) |
Out - of - round and taper of cylinder bore : |
Max. 0.02 mm (0.0008 in.) |
If a ridge exists at the top of the cylinder, cut it off with a ridge reamer.
Oversize pistons are available in four sizes.
Piston service size and mark mm (in.) |
0.25 (0.010) O.S : 0.25 |
0.50 (0.020) O.S : 0.50 |
0.75 (0.030) O.S : 0.75 |
1.00 (0.040) O.S : 1.00 |
To rebore the cylinder bore to the oversize, maintain the specified clearance between the oversize piston and the bore and make sure that all used pistons are the same oversize. The standard measurement of the piston outside diameter is taken at a level of 12mm (0.47 in.) above the bottom ofthe piston skirt and across the thrust faces.
Piston-to-cylinder clearance : |
0.03 - 0.05 mm (0.0012 - 0.0020 in.) |
Check for damage or cracks in the cylinders.
Check the top surface of the cylinder block for flatness. If the top surface exceeds the limit, grind to the minimum limit or replace.
Standard value |
Flatness of gasket surface : |
Max. 0.03 mm (0.0012 in.) |
Service limit |
Flatness of gasket surface : 0.05 mm (0.0020 in.) |
When the cylinder head is assembled, grinding less than 0.2mm (0.008in.) is permissible.
Oversize pistons should be selected according to the largest bore cylinder.
Identification Mark | Size |
0.25 | 0.25 mm (0.010 in.) |
0.50 | 0.50 mm (0.020 in.) |
0.75 | 0.75 mm (0.030 in.) |
1.00 | 1.00 mm (0.040 in.) |
The size of piston is stamped on top of the piston.
Measure the outside diameter of the piston to be used.
According to the measured O.D., calculate the new bore size.
New bore size = Piston O.D + 0.03 to 0.05 mm (0.0012 to 0.0020 in.) (clearance between piston and cylinder) - 0.01 mm (0.0004 in.) (honing margin.)
Bore each of the cylinders to the calculated size.
To prevent distortion that may result from temperature rise during honing, bore the cylinder holes in the firing order.
Hone the cylinders, finishing them to the proper dimension (piston outside diameter + gap with cylinder).
Check the clearance between the piston and cylinder.
Standard : 0.03 - 0.05 mm (0.0012 - 0.0020 in.) |
When boring the cylinders, finish all of the cylinders to the same oversize. Do not bore only one cylinder to the oversize.
