Piston Knocking Noise Correction

Fig. 12 Measuring piston diameter:

When measuring piston diameter, place micrometer 3/16 inch below cross slot or 3/8 inch below oil ring groove, Fig. 12. Cylinder liner diameter is measured by placing a micrometer two inches down from top of liner and perpendicular to cylinder center line. The difference between the two readings should be .0010---.0018 inch. Cylinder bore out-of-round should not exceed .0008 inch and piston bore taper should not exceed .0005---.002 inch. If any reading is not as specified, piston and cylinder liner assembly must be replaced. No attempt should be made to rebore or hone cylinder liners. Refer to "Cylinder Liner, Replace" for procedure.

Fig. 13 Off centered piston pin. V8-250:

On some 1982-85 V8-250 engines a minor to severe internal metallic knock may be encountered. This may be caused by close piston to counterbalance tolerance on cylinder Nos. 1, 2, 3, 6, 7 and 8 and is usually heard when engine is at operating temperature between 800---1400 RPM.

Caution: Before proceeding be sure to consult applicable Technical Service Bulletins.

The following procedure should be used to correct this problem:
1. Remove engine oil pan and cylinder heads as previously described.
2. Inspect all pistons for correct installation.
3. Using a wax pencil, mark right and left sides of outboard piston skirts which rotate next to crankshaft counterbalance weights on piston Nos. 1, 2, 3, 6, 7 and 8.
4. Remove and inspect all pistons for off-centered piston wrist pins, Fig. 13. If off-centered piston pins are encountered, replace piston and liner assembly.
5. Using a suitable file, remove a small amount of material from piston skirt edges marked in step 3. All surfaces must be smooth and free of all file marks after reworking. If interference marks are evident in the piston skirts and filing does not remove marks, replace piston and liner assembly.
6. Reinstall pistons into block.
7. Check piston skirt to crankshaft counterweight clearance by placing an index card between skirts and counterweights while rotating crankshaft. No drag should be felt on card. If drag is felt, crankshaft should be replaced.
8. Reinstall cylinder heads and oil pan.