Usage:
3408 And 3412 Engines
Reference: Service Magazine, September 14, 1981, Page 9. The article, "Exhaust Manifold And Air Lines Changes ..." lists several Service Magazines that were about exhaust manifold leakage and broken studs.
Larger stainless steel studs can be used as a replacement for broken exhaust manifold studs on early 3408 and 3412 Engines with flange-type exhaust manifolds. These new studs are only to be used with the rear exhaust manifolds. The new studs can be used instead of the new manifolds in the reference articles to prevent broken studs.
The new studs are 7/16" in diameter and new nuts, tubes and washers will be needed with them. See the chart. The former studs were 3/8" in diameter.
NOTE: Installation of larger studs for the rear exhaust manifold will result in the use of two different size studs, nuts and washers on the same cylinder head. It is possible that this can cause a problem if the dealer has an exchange program.
INSTALLATION: To use the 7/16" studs:
1. Make the clearance holes in the rear exhaust manifolds and the gaskets 12.20 mm (.484") in diameter.
2. Drill the existing holes in the cylinder block to 9.5 mm (.375") diameter and a depth of 18.0 mm (0.71").
3. Use a 7/16"-14 tap to cut new threads.
4. Install the new studs.
5. Tighten the nuts to a torque of 72 ± 8 N·m (51 ± 6 lb ft).
