LO 8-13 Outline the scope of cylinder block service and describe common service operations

Counterbores and Liner Protrusion

Ensuring that cylinder liners protrude or extend above the block deck by the correct amount is one of the most critical operations for engine technicians. Without enough protrusion, a liner can move in the block, resulting in rapid wear, leaks, and block damage. If there is too much protrusion, the cylinder head gasket cannot seal properly. Uneven protrusion between liners results in compression and coolant leaks, cracked liner flanges, liner movement, and warped cylinder heads. Liner counterbores or ledges (where the liner sits in the block) must be carefully inspected before liners are installed to ensure that they are square and cut to the correct depth. The counterbore may need to be shimmed if liner protrusion is too low or cut and shimmed if the liner sits too high and the counterbore is damaged in any way. Anytime a liner is installed, the protrusion must be measured. Liner counterbores can be repaired with cutting and machining. A liner with inadequate protrusion can be raised with the installation of a shim beneath the liner flange Figure 93.

FIGURE 08-93: A liner with insufficient protrusion or a block that has a machined counterbore can be raised with a shim beneath the liner flange. Shim thickness is calculated after measuring counterbore depth, liner flange, and desired protrusion.

Top-stop flange breakage is usually caused by excessive flange loading because of significant pressure that was applied to the flange through the cylinder head clamping forces. The cylinder head gasket distributes a large amount of clamping force over the block deck, but if it is accidently left uninstalled when the cylinder head is tightened, all the liner flanges will crack and break due to the localized clamping forces. Flange breakage can also result from the following conditions:

• Improper torqueing of the cylinder head during a rebuild
• Uneven flange height above the deck
• Uneven wear in the cylinder block flange counterbore if liners are not uniform in protrusion or are not parallel to the block deck
• Worn inner edge of the flange counterbore seat (in the cylinder block), causing the flange to tilt downward
• Improper positioning of the head gasket fire ring

To measure liner protrusion, follow the guidelines in Skill Drill 8-2.