3406 Truck Engines
Service information from The Jacobs Manufacturing Company has given a torque specification of 35 to 40 N.M (25 to 30 lb ft) to tighten the locknuts on the valve clearance adjustment screws. This torque is too high, and has caused damage to the adjustment screws on some engines.
To prevent this possible problem, a revision will be made to their service information as soon as possible. The later specifications will show a torque of 28 to 35 N ·m (22 to 25 lb ft), which is within (inside) Caterpillar specifications for these engine models.
Make a note of this torque in any service information you have from The Jacobs Manufacturing Company. Be sure to use the correct torque during service work on engines equipped with the Jacobs Engine Brake.