Usage:
CONFIDENTIAL TIBU3662
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TECHNICAL INFORMATION BULLETIN |
July 31, 2002 |
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Wheel Loaders |
992G (7HR1-UP, ADZ1-UP) |
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Component Code(s) 6118 |
SUBJECT: EARLY DETECTION CAN PREVENT CRACK GROWTH INTO A-PIN BORE
PROBLEM:
7HR1-311 Machines 7HR312-Up and ADZ1-Up Machines
Under certain conditions, cracks can develop around the boom-to-frame pin bore. The cracks generally start from the weld for the pin flag retention block and/or from imperfections left around the bore after line boring. Older machines are equipped with a retention block that is mounted directly on the frame, while later machines are equipped with a "D"-plate to which the retention block is mounted. The arrangement of a particular machine can be determined by visual inspection.
Crack into Parent Material Crack from Line Bore Imperfection
If a crack develops and goes undetected, serious problems can arise. However, if the crack is detected while still in the weld material, it can be cut out and re-welded. Once the crack spreads into the parent material (frame), the repair procedure becomes more involved
SOLUTION:
Example of small developing cracks.
The critical welds should be inspected periodically. Early cracks sometimes look like insignificant rusty scratches, and could be easily missed.
The repair procedure will vary depending on the severity of the crack. Use a crack repair method that is appropriate for the crack size. For example, the crack could be ground out, welded, then the weld ground smooth. For a larger crack, it may be necessary to remove the crack with a carbon arc, then weld it and grind it smooth. For complete guidelines, see the Cat Service Welding Guide.
If the crack has reached the bore, contact a Large Wheel Loader Product Support representative for further information. Contact:
Nick Boss (630) 859-5942
Rich Piercy (630) 859-5520
Doug Long (630) 859-4294
Critical Note: After frames are line-bored, closely inspect the bore for any imperfections such as notches, weld pops, or grinding gouges or scratches. Such imperfections could give a crack a propagation point. They should be repaired and ground smooth before assembling the joint.
Preventative Solution: One method that has increased a weld?s resistance to cracking is to locally grind the weld toe. The weld should be ground to a maximum depth of .8mm (.03in)(A). The weld should be ground on the top and bottom of the "D" plate for approximately 75mm (3in)(B). Be sure not to over grind into the frame or grind too much of the weld throat. Use a burr grinder instead of a disc grinder.
The grinding procedure should produce a smooth, concave profile.