Usage:
All 3406 Engines (Except those equipped with an aftercooler)
Description of Change: A new air inlet manifold is used in the above engines. This new manifold has longer bolt bosses to increase the depth of the thread .25" (6.4 mm). With this change, .25" (6.4 mm) longer bolts are used to give the extra thread engagement needed to keep these bolts tight.
Adaptable As: The new inlet manifold is a direct replacement for the former manifold when longer bolts are used. This new manifold was first used on engines that have the serial numbers shown in the chart that follows:
This manifold is also adaptable for field conversion of 3406 Engines with Serial Numbers 90U1-up, 92U1-up, and 70V1-up.
The parts in the factory change are shown in Chart A.
The parts needed for the field conversion are shown in Chart B.
Field Conversion
For a field conversion, it is necessary to make a modification of the former 4N9049 Inlet Manifold. The steps for the modification follow:
1. Drill the two end bolt holes through with a 27/64" drill.
2. Retap (cut threads again) the other bolt holes with a 3/8-16 bottom tap.
3. Machine the flange (spot face) or use a file on the top side of the two end bolt bosses, so the washer will have a flat seat. But do not decrease the thickness of the manifold in this area to less than .5" (13 mm). Also, be careful not to make a sharp corner in the area shown in the illustration.
4. Install the manifold with new 6N8204 Gaskets and the longer bolts (S1590 and S1591).
Instruction for field conversion.