COVER 2074271 - Caterpillar

TECHNICAL INFORMATION BULLETIN January 14, 2004
WHEEL LOADER 994 (9YF1-UP)
994D (3TZ1-295)
Component Code 5104SUBJECT: An Improved Piston is available for the 994 Tilt Cylinder.
PROBLEM:
The 114-2824 Piston may develop cracks at the bottom edge of the seal groove. The cracks may eventually propagate and result in large pieces of material separating from the piston as shown in the picture below.
There have also been reports of the piston cracking at the thread recess located in the ID of the piston. The cracks are due to stress relief. There is no evidence that the stress relief cracks in this area propagate or lead to failure of the piston.
SOLUTION:
A new 229-9549 Piston is available to resolve both of the above issues. The distance between the seal groove and face of the piston has been increased from 13mm to 22mm. This reduces the stress concentration in the bottom of the seal groove and will eliminate cracking in this area. In addition the piston material has been changed from ductile iron to alloy steel with a heat treat procedure. This increases the strength of the piston greatly and will resolve the stress relief cracking on the ID of the piston and provide added protection against cracks initiating in the seal groove.
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