Piston to Cylinder 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.





CYLINDER BORE DIAMETER GAUGE
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 B when measured at the center of the piston travel.

Measure the piston outer diameter as described 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.

If installing new rings in a used cylinder that has not been refinished, remove the cylinder wall glaze using only spring-loaded Engine Cylinder Hone Set 303-S084 (T73L-6011-A). Remove only if there is no visible sign of cross-hatch markings on the cylinder walls.Always clean the cylinder bore thoroughly with detergent and water solution.

1. Calculate size of piston to be used by taking a cylinder bore check.

NOTE: After any refinishing operation, allow cylinder bore to cool. Make sure piston and bore are clean and dry before checking piston fit.

2. Select proper size piston to provide desired clearance. Measure piston diameter in-line with centerline of piston pin and at 90 degrees to piston pin axis.
3. Make sure piston and cylinder block are at room temperature, 21°C (70°F).

Measure the piston diameter to obtain the specified clearance. 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.