MANIFOLD-EXHAUST 9Y1231 - Caterpillar

3406, 3408 Truck EnginesWe have had some reports of valve failure on 3406 and 3408 Truck Engines. In some cases, valve failures are caused by loose bridge adjustment locknuts and/or too much valve lash. When the bridge adjustment locknuts are loose, it is possible for the valve lash to change.
Valve lash can also change if the locknut for the valve lash adjustment screw is loose. This can damage the valves and cause a valve failure.
On new or rebuilt engines, our recommendation is to measure and adjust the valve lash after 80 000 km (50,000 miles). Valve lash must be adjusted again at 160 000 km (100,000 miles). After that, valve lash must be adjusted at 160 000 km (100,000 mile) intervals.
Before the valve lash is adjusted, make sure the bridge adjustment locknut is tight. The complete procedure for valve lash adjustment is given in the 3408 Truck Engine Operation and Maintenance Guide, Form SEBU5673 and the 3406 Truck Engine Operation and Maintenance Guide, Form SEBU5595-01.