ENGINE AR-CORE 3940447 - Caterpillar

TECHNICAL INFORMATION BULLETIN DECEMBER 02, 2005
EXCAVATORS 312B (9GR, 9HR, 2NS, 3ES, 6SW, 9NW), 312B L (8JR, 3FS, 9FS, 2KW), 312C (CAE1-3071, BNN, DBN1-495, FDS1-431), 312C L (CBA1-2949, BWH1-880, CBT) EXCAVATORS
Component Code(s) 6505SUBJECT: THE BOOM MAY CRACK AT THE CENTER BOSS ON CERTAIN
EXCAVATORS
PROBLEM:
The welded butt joint between the boss assembly and the side plate for the boom assembly may crack. Undesirable weld quality and the incorrect location of the back up strips in the boom assembly can cause the cracks at the welded joint.
SOLUTION:
Improved weld quality and a new location for the back up strip have been applied to the boom assemblies that are currently being manufactured. If the welded joint at the center boss on the boom assembly cracks, use the following procedure and repair the cracked weld.
Illustration 1. Typical Weld Crack At The Center Boss
(A) Crack
Repair Procedure For Weld Cracks In The Boom Center Boss
Disassemble the stick and the boom from the machine. Refer to the Disassembly and Assembly Manual that is appropriate for your machine.
Illustration 2. Grind Weld Flush
Grind the weld flush with the plates.
Use penetrating dye and confirm the length of the crack in the welded joint.
Illustration 3. Remove Crack
Use a grinder or air arc and gouge out the crack from the welded joint. Gouge out to the back up strip.
Illustration 4. V-Groove
Grind the gouged out area in order to create a V-groove joint.
Note: Make sure that the surface is clean. Remove any residual carbon spots, slag, or splatter that remained from the gouging operation. Use penetrating dye and make sure that the crack was totally eliminated.
Illustration 5. Finish Weld
Remove any traces of moisture from the V-groove. Weld the joint with standard weld material.
Note: Make sure that the angle between the top of the final weld pass and the top of the plate is smooth. If the angle is not smooth, grind the surface until it is flat.
Remove any weld slag or splatter from the welded area.
Use an ultrasonic test and make sure that no new defects were created during the repair procedure.
Illustration 6. Fabricated Reinforcement Plate
(B) 700 mm (27.5 inch) (H) 15 mm (0.6 inch)
(C) 450 mm (17.7 inch) (K) 500 mm (19.7 inch) radius
(D) 305 mm (12.0 inch) diameter (L) 989.3 mm (38.9 inch)
(E) 1190 mm (46.9 inch) radius (M) 34 mm (1.3 inch)
(F) 230 mm (9.0 inch) (N) 212.5 mm (8.4 inch) radius
(G) 177 mm (7.0 inch) (P) 253 mm (10.0 inch)
Refer to Illustration 6 and a 283-8949 Boom Assembly in order to fabricate the reinforcement plate. Fabricate the reinforcement plate from steel plate that is 10 mm (0.4 inch) thick. Fabricate two plates if the welds are cracked on both sides of the boom. Procurement of the new 283-8950 Plate is an alternative to fabrication.
Remove any oil, paint, or dirt from the edge of the reinforcement plate.
Illustration 7. Boom With Reinforcement Plate
(A) 60 mm (2.4 inch) (H) 15 mm (0.6 inch) radius
(C) 10 mm (0.4 inch) (J) 25 mm (1.0 inch)
(D) 117-5604 Stud (K) 55 mm (2.2 inch)
(E) 305 mm (12.0 inch) diameter (L) 160 mm (6.3 inch)
(G) Fabricated plate (N) 290 mm