PLATE 8T6651 - Caterpillar

WHEEL LOADERS
994 (9YF1-221),
994D (3TZ1-264) LARGE WHEEL LOADERSProblem:
The 6E-6197 hydraulic system relief valve setting on certain machines may be set too high if the current Test and Adjust procedures are not used. For the 994, the current procedure is SENR4753-02, effective Jan 01, 1999. For the 994D, it is RENR2513. Also, hydraulic system relief valve adjustment procedures in the Special Instructions for assembly of both 994 and 994D models are incorrect. (994: SEHS9932; 994D: REHS0351) This can result in reduced life of the lift cylinder head bolts, head seals and rod seals. The former procedure can sometimes open the TILTBACK line relief valve instead of the system relief valve. When this happens, further adjustment increase of the system relief valve may reach its adjustment limit by starting to close the valve, but with no indication of this at the system pressure tap. Subsequent operations will cause excessive cylinder pressures.Solution:
Though not mandatory, the 7J2546 pin (29 mm long) should be removed from the 6E-6197 valve group and be replaced with a shorter 7B5684 pin (27 mm long). This extends the adjustment range of the valve to reduce the possibility of excessively high settings. Disturbing the setting of the valve can be avoided by separating the valve at the larger joint rather than removing the setting screw. Reassemble and torque the joint to 110 10 N M.Verify that system relief pressure settings are correct when tested by the current method above. The current method requires that the engine be set at HIGH IDLE and the BOOM DOWN circuit be stalled. (The method prior to Jan 01, 1999 required that the engine be set at LOW IDLE and the TILTBACK circuit be stalled.) Increase the boom down pressure carefully so that the system pressure does not exceed the upper limit specified. (There is no line relief valve in the boom down circuit to limit the pressure if the system relief valve is set too high.) Disregard machine effectivity reported on this subject in Service Magazine SEPD0279-00, dated Nov 06, 1995.COPYRIGHT 2000 CATERPILLAR ALL RIGHTS RESERVED