1990/02/01 Caterpillar

3408, 3408B Truck Engines

Reference: Truck Engine News: November 1988, Page 1,"New Liner Seat Insert Available " for 3400 Family Of Engines equipped with spacer plates.

January 30,1989; Page 1, "New Head Gasket Available (Used); Head Gasket Replacement Guidelines " for 3406 Family Of Truck Engines.

August 1989; Page 1 "Improved Head Gasket Used; Summary Of Earlier Gaskets And Service Tips " for 3406, 3406B Family of Truck Engines.

Reference: Guidelines For Reusable Parts, SEBF8131, "Spacer Plates For 3406 Family Of Engines. "

Description of Change: A new 7E7308 Cylinder Head Gasket is used on 3408B Truck Engines. The new gasket has the following improvements over the former gasket.

... A thicker fire ring to compensate for the asbestos-free body material. The thicker fire ring and thinner wrap help to prevent leakage of combustion gases, and give a better "crush" on the liner flange when the head is tightened.

... The overlap of the stainless steel fire ring wrap is reduced to give better gasket body loading and minimize the possibility of fluid leaks. The wrap has a tab-style design. This tab design results in a more flexible gasket that requires extra care in handling and storage.

... This gasket is NOT coated on the cylinder head side. It DOES have a single layer of black Teflon ®(PTFE) on the spacer plate side. The PTFE prevents sticking to the aluminum spacer plate.

Adaptable To: The new 7E7308 Gasket is a direct replacement for the former 2W7984 Gasket which has been canceled. The new 7E7308 Gasket is effective with 3408B Truck Engine 28V4837.

NOTE: Any time the new head gasket is to be installed, refer to the following topics so that maximum life can be obtained from the new gasket, head, block, spacer plate, and engine block.

Liner Projection and Machining the Block and/or Head

Do NOT adjust the liner projection above the block if it measures in the range of 0.03 to 0.15 mm (.001 " to .006"). ALSO, make sure that the differences between all four measurements at any one cylinder do not exceed 0.05 mm (.002 "). AND, the difference between the average projection of two liners next to each other must not exceed 0.05 mm (.002 "). These specifications are in the Service Manuals for these engines.

Wear or erosion under the liner flange will require use of a stainless steel insert. Read the reference article about the new liner seat insert. The head and/or block surfaces may have been damaged if the engine was operated extensively after a head gasket failure

The maximum amount of material that can be machined from the top deck of the block is controlled by the minimum dimension from the crankshaft centerline to the top deck on the block. This minimum is 425.02 mm (16.733 "), and is also in the Service Manuals. Use the 6V7840 Deck Checking Tool Group to measure this dimension. Special Instruction SEHS8187 explains the use of this device.

There is also a minimum allowable thickness for the head. This is 111.51 mm (4.390 "), and limits the amount of material that can be taken off the bottom of the head.

Retightening Head Bolts

After installing the new 7E7308 Gasket, retightening the head after a road test or dynamometer test, or at the first scheduled check for valve lash is not necessary. The thicker fire ring and the reduced fire ring wrap increase the combustion seal and gasket body loading, which reduces the need for subsequent retightening. Remember, either of these gaskets can be identified on the engine by the filled-in ends as shown.

Engines using the later 2W7984 Gasket should have the head bolts retightened. These two gaskets have no asbestos, and they use the standard thickness fire ring and wrap.

The cylinder head bolt torque, regardless of whether tightened only once or retightened, is 450 ± 20 N·m (330 ± 15 lb ft). Follow the bolt tightening sequence in the Service Manuals, and tighten in three or four steps to ensure uniform loading.