Usage:
3500 Family of Engines;
D11N, 776B Tractors;
777B, 785, 789 Trucks
A severe engine overspeed can cause damage to the inlet valve rotocoil assembly. This damage could make the rotocoil assembly unable to retain its valve. This could result in considerable engine damage. Also, repeated engine overspeeds can result in crankshaft bearing damage and/or failure.
(1) Inlet valve. (2) Lock (keeper). (3) Rotocoil assembly. (4) Valve spring.
A severe engine overspeed results in high loads on the inlet valve and rotocoil such that the inlet valve and keepers are driven down into the tapered bore of the rotocoil. Cracks from on the lower end of the tapered bore of the rotocoil. If the damage to the rotocoil tapered bore is severe enough, the valve keepers may be forced completely through the rotocoil and allow the valve to contact the top of the piston. The result is damage to the valve, piston, and head. It could also result in damage to the turbocharger and other cylinders.
If an overspeed is suspected, inspect the inlet valve rotocoils for evidence the rotocoils are moved up higher on the valve stem. If any rotocoils are cracked, Caterpillar recommends replacement of all the inlet valve rotocoil assemblies.