Usage:
D11N Track-Type Tractors;
776B, 776C, 784B Tractors;
777B, 777C, 785, 785B, 789, 789B, 793, 793B Trucks;
994 Loaders;
5130, 5230 Excavators Powered By 3508, 3512, And 3516 Machine Engines
Description of Change: A new exhaust valve with a tapered stem is used in the cylinder head groups on the engines in these machines. The new exhaust valve stem tapers from a diameter of 9.441 mm (.3717 in) at point (A) to a diameter of 9.335 mm (.3675 in) at point (B) as shown in the illustration. This gradual change in diameter provides additional clearance between the bottom of the valve guide and the valve stem. This will compensate for differential thermal expansion between the valve and the valve guide. The new exhaust valve will help prevent valve stem scuffing and/or sticking.
Adaptable To: The new 121-9839 Exhaust Valve is a direct replacement for the 7E-4609 Exhaust Valve in cylinder head groups identified in the chart. The new exhaust valve is in effect with 3508 (99W3480, 7YG1246) Machine Engines. The new exhaust valve is in effect with 3512 (96Z912, 4WJ591) Machine Engines. The new exhaust valve is in effect with 3516 (54Z1095, 2PK771) Machine Engines
Location of the tapered area on the new 121-9839 Exhaust Valve. (A) = 9.441 mm (.3717 in). (B) = 9.335 mm (.3675 in).
