Usage:
D346, D348, D349 Engines
Reference: Caterpillar Tool Guide, Miscellaneous Tools Section, "Thread Inserts (Heli-Coil), Taps and Installation Tools For Repairing Damaged Threads".
Description of Change: This article supersedes a similar article in Service Magazine, September 22, 1986, Page 10. Put a mark through the article "Longer Adjusting Screw and Jam Nut Available For Use In Valve Rocker Arms" and add a note referring to this article.
The 8T8907 Nut should not be used with the 7C1644 Screw Assembly. Instead, use thread inserts (Heli-Coils) to repair rocker arms with worn or loose threads. Heli-Coils may be used with either the longer, 7C1644 Screw Assemblies or the shorter 2S323 Screw Assemblies, which are being reinstated for parts service. Use of Heli-Coils in worn rocker arms will extend the serviceable life of the rocker arms while avoiding the expense of buying special longer screw assemblies and jam nuts.
There have been reports of excessive wear in the threads of the 1P7304 Rocker Arm and 2S323 Screw Assembly. These are a part of the 1P7310 Rocker Arm Assembly shown in the illustration. The excessive thread wear may cause valve misadjustment and may lead to valve or rocker arm failure.
The repair announced in the previous article should not be used because the 7C1644 Screw Assembly is hardened over its entire length. Use of a jam nut with this screw assembly may cause a brittle fracture in the screw assembly when either the jam nut is tightened down or shortly after the repaired engine is put back in service.
Adaptable To: Worn or loose rocker arms can be repaired on all the above engines when the following procedure is used.
Procedure To Check For Excessive Thread Wear
NOTE: This should be done either at engine overhaul time or if valve adjustment has been a problem. Use the Service Manual as a reference.
1. Remove the camshaft housing.
2. Remove the 2S323 Screw Assembly from the 1P7304 Rocker Arm. It is necessary to remove the screw assembly so the 2S3992 Spring and 2S3991 Plunger in the rocker arm do not put a side force on the screw assembly. See illustration.
3. Install the screw assembly in the rocker arm from the opposite side that it was removed.
4. Check for excessive movement between the threads of the screw assembly and the rocker arm. Compare the movement with a new rocker arm assembly to determine what is acceptable.
5. If excessive movement is felt, replace the screw assembly with a new one and repeat the test.
6. If there is excessive movement using the new screw assembly, it will be necessary to install a Heli-Coil in the worn rocker arm. Install 8T2737 Inserts (7/16"-20 Thread) using the tools and procedure given in the Caterpillar Tool Guide.
1P7310 Rocker Arm Assembly.