PIN 1285010 - Caterpillar

All 3408, 3408B and 3412 EnginesSUPPLEMENT: 05/20/85SERVICE MAGAZINE, APRIL 8, 1985, PAGE 4.In the article "Changes To Exhaust Manifolds Help Prevent Broken Studs," add the following to "ADAPTABLE TO:" The new 6V5699 Taperlock Stud is a direct replacement for the former 4S6137.--------------- END SUPPLEMENT ---------------Description of Change: Several changes have been made to prevent the exhaust manifold studs on 3408 and 3412 Engines from breaking. These changes include new studs, larger stud holes on the end manifold sections and anti-seize compound on the manifold slip joints. The new studs are made from a high temperature stainless steel. They will not relax under the high temperatures incurred during engine operation, so the manifold-to-head joints will remain tight. Since the manifolds remain tight, any movement from thermal expansion occurs in the slip joints. The new studs are 4.0 mm (.16") longer than the former studs, and they are marked with an "X" on the end. The former studs are marked with a "Y."
The stud holes in the end manifold sections (8N990 and 8N991 Manifolds) have been enlarged from 10.5 mm (.41") to 11.5 mm (.45"). The additional clearance allows more thermal expansion without interference with the studs.
Anti-seize compound is now used on the slip joints. Rusted or seized joints cause the manifold sections to expand as a single-piece unit, placing the expansion force on the studs. The anti-seize compound keeps the joints free to allow movement from the expansion.
Adaptable To: These changes are adaptable to all 3408 and 3412 Engines. The use of stainless steel studs became effective with the Serial Numbers shown in the following chart.
The stud holes in any single port manifolds can be drilled out to the larger 11.5 mm (.45") dimension. Double-port manifolds already use the larger holes.
When broken manifold studs are replaced, always remove, disassemble and clean the manifold. Then, apply a coat of 5P3931 Anti-Seize Compound to the slip joints before reinstalling the manifold.