An overhead adjustment on a CAT engine sets the correct valve lash and jake brake lash to factory specifications. This ensures proper airflow, combustion, and brake operation, preventing power loss and premature wear.

 CAT generally recommends setting the overhead at the first 100,000–150,000 miles (160,000–240,000 km) or after major top-end work, then every 250,000–300,000 miles (400,000–480,000 km). Always verify in the engine’s service manual.

If lash is too tight, valves may not fully close, causing power loss and burned valves. If lash is too loose, you’ll have noisy operation and accelerated wear on the valve train components.

If you have mechanical experience and the correct tools, you can. However, incorrect adjustment can damage the engine. Always follow the manufacturer’s procedure and torque specs.

This calculator includes common torque values for rocker shaft bolts, locknuts, and jake brake settings, in both ft-lb and Nm, for multiple CAT engine families.

Cold means the engine is at ambient temperature — it hasn’t been running long enough to build heat in the head, block, or oil. Usually, “cold” lash is set after the engine has been off for several hours, ideally overnight.

Hot means the engine has been run to normal operating temperature, oil is warm, and metal components have expanded. Hot lash specs are sometimes different from cold specs because heat changes clearances.

Most CAT overhead settings are specified as cold in service manuals, unless otherwise noted. Always confirm in the manufacturer’s procedure.