Usage:
3408 and 3412 Engines in All Applications
Reference: This article replaces an article with the same title in the October 25, 1976 Service Magazine. Put a mark through that article and refer to this new article. When a Remanufactured Cylinder Head is installed on any 3408 or 3412 Engine with numbers lower than those listed in this article, new rocker arm brackets must be used so oil will reach the rocker arm shaft. This is the REASON for reprinting this article. It is intended for any one who might install a Remanufactured Head on one of these very early engines.
Description of Change: Several years ago the cylinder heads and valve rocker arm brackets were changed on the 3408 and 3412 Engines. The new heads and rocker arm brackets have the oil supply passages for the rocker arm mechanism in a different location than the former parts. See Illustrations 1, 2 and 5. In addition, the top of the new cylinder heads have more material around the core plugs for added strength.
Illustration 1. Design of new and former oil supply passages in cylinder head and rocker arm brackets.
A new gasket is used between the cylinder block and the spacer plate. This new gasket has a coating of rubber so the gasket will not stick to the cylinder block and plate. This will make disassembly easier.
Illustration 2. Location of oil supply passage in cylinder head for 3408 and 3412 Engines.
Adaptable To: The new parts are adaptable to earlier engines when the new cylinder head, bracket assembly, and brackets are used together as shown in the chart. The new gasket is a direct replacement for the former gasket which is canceled.
The former 4N833 Brackets are still serviced for use only with the 4N7799 or 4N7800 Head Assemblies.
The new parts are first used on engines with the serial numbers shown in the chart.
INSTALLATION: Illustration 3 shows the specific locations where the different rocker arm brackets must be installed on 3408 Engines when the 7N858 Head Assembly is used.
Illustration 4 shows the specific locations where the different rocker arm brackets must be installed when the 7N848 Head Assembly is used.
The 7W6800 Bracket Assembly MUST be used in the locations shown by an "X" to get oil to the rocker arm shaft. Either the 7W6800 or 7W6803 Brackets can be used at the opposite end of the rocker arm shaft to close the drilled passage in the shaft.
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DO NOT use a 4N833 Bracket at these locations to close the drilled oil passage in the opposite end of the shafts, because this will permit pressure oil around the head bolts. The result can be oil leaks into the coolant.
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The 7W6803 Brackets are normally used at the center locations, but some engines have the 4N833 Brackets installed at the factory.
Illustration 3. When a 7N858 Head Assembly is used on a 3408 Engine, the brackets marked "X" MUST contain an oil supply passage to the rocker arm shafts.
Illustration 4. When a 7N848 Head Assembly is used on a 3412 Engine, the brackets marked "X" MUST contain an oil supply passage to the rocker arm shaft.
Illustration 5. Differences between the former bracket and the two new brackets.