Piston To Cylinder Bore Clearance

NOTE: Cylinder bore must be clean and dry, and cylinder block must remain at room temperature (21°C/70°F) for eight hours before taking cylinder measurements.





Measure cylinder bore diameter in two directions, A and B.
Measure cylinder bore diameter in both directions at 12.70 mm (1/2 inch) below top of cylinder block deck.
Measure cylinder bore diameter in both directions at 12.70 mm (1/2 inch) above top, of the piston with the piston at its lowest point of travel in the cylinder block bore.
The cylinder bore service limit Equals the average of measurements A and B when measured at the center of the piston travel.
The cylinder bore taper equals the difference between measurements A at top and B at bottom of cylinder bore.
The cylinder bore out of round equals the difference between measurements A and 1B when measured at the center of the piston travel.
Measure the piston outer diameter to make sure the specified clearance is obtained. It may be necessary periodically to use another piston (within the same grade size) that is either slightly larger or smaller to achieve the specified clearance.
If none can be fitted, refinish the cylinder to provide the proper clearance for the piston.
When a piston has been fitted, mark it for assembly in the cylinder to which it was fitted.
If the taper, out-of-round and piston-to-cylinder bore clearance conditions of the cylinder bore are within specified limits, new piston rings will work well.