1985/11/11 Caterpillar

All 3500 Series Engines With Dry Exhaust Manifolds

Exhaust manifold head gasket leaks can be caused by loose or broken bolts that fasten the exhaust manifolds to the cylinder heads. Investigation indicates that these leaks usually occur after one or more exhaust manifold sections have been disconnected from the cylinder head. The following is a list of the most common causes for the loose exhaust manifold bolts.

1. The exhaust manifold bolts are under torqued.

2. The surfaces of the exhaust manifold and/or the cylinder head that contacts the exhaust manifold gasket are not clean and free of foreign material. The bolt holes in the cylinder head are not clean.

3. The exhaust manifold expansion joint bolts are not loosened before the manifold is tightened onto the cylinder heads. The tight expansion joints can hold the manifold away from the cylinder heads.

4. The incorrect installation or misalignment of the turbocharger air piping can cause misalignment of the exhaust manifolds on engines with center mounted turbochargers.

The torque specification for the bolts that fasten the exhaust manifolds to the cylinder heads has been increased to 55 ± 7 N·m (40 ± 5 lb ft). This increases the clamping force on the gasket between the manifold and the cylinder head and decreases the possibility of an exhaust manifold gasket leak. Use the INSTALLATION PROCEDURE that follows to prevent a problem after a repair.

Installation Procedure

1. For engines with centrally mounted turbochargers, check the air piping to the turbochargers. The turbochargers must be correctly aligned and should not support excessive piping weight.

2. Be sure the exhaust manifold and cylinder head surfaces that contact the exhaust manifold gasket are clean and free of any foreign material.

3. Be sure the bolt holes in the cylinder heads have good threads. Also, be sure there is no dirt or fluid in the bolt holes.

4. Loosen the bolts on the exhaust manifold expansion joints where the repair is being made (loosen all the expansion joint bolts if the entire manifold is being installed). Be sure the manifold sections can be moved in the expansion joints.

5. Put the exhaust manifold and new exhaust manifold gasket in position on the cylinder head. If required, use a hammer and piece of wood to put the manifold into position against the cylinder head.

6. Put 5P3931 Anti-Seize Compound on the exhaust manifold bolt threads before installation. Tighten the bolts to a torque of 55 ± 7 N·m (40 ± 5 lb ft). After all the bolts are installed, tighten them again to the same torque.

7. Put 5P3931 Anti-Seize Compound on the threads of the expansion joint bolts that were loosened. Tighten the bolts to 45 ± 7 N·m (32 ± 5 lb ft).