W E Ld In - GMC 1986 P-Truck Service Manual

2A-6 FRAME
13. Straight Crack
14. Sunburst Cracks
Figure 2—Types Of Frame Cracks
3. " V" grind the entire length of the crack from the
starting point to the 6 mm (0.25-inch) hole at the
extreme end.
4. The bottom of the crack should be opened up 2
mm (1 /ie-inch) to allow good penetration of the
weld. (A hack-saw blade may be used for this).
5. Weld with proper electrode and proper welding
techniques. See " Welding" outlined later in this
section for tips on welding.
6. Grind the weld smooth on both the inside and the
outside of the rail or crossmember. Be extremely
careful to eliminate weld build-up or notches on
the edge of the flange.
WELDING
Improper welding techniques are the cause of many
weld and/or frame failures. The following information
points out potential areas of difficulty and provides
some general guidelines for successful frame welding.
Most weld failures occur at the end of the weld in
areas of the frame that are under high stress. By
elim inating the ends of a weld, failures can be
reduced; this can be done by making a hole or slot in
the part to be attached and then using a fillet weld
around a slot or plug weld. Do not leave a notch at the
end of a weld.
Over-welding can be harmful, especially if it is in an
area of the frame that receives high concentrations of
stress.
Small cracks in a crossmember may be welded (see
" Repairing Cracks" previously outlined in this section).
When welding:
1. Do not use oxyacetylene welding equipment.
2. W henever possible, use sm a lle r diam eter
electrodes and make several passes; this is
preferred to using a large diameter electrode and
making fewer passes.
3. Do not use more heat than is necessary to give
good penetration.
4. Do not run more passes than necessary.
5. Make sure the weld is free from craters and
undercuts.
6. Make sure sca le is rem oved from each
successive pass.
7. If repairing a crack, grind the surface of the weld
flush with the parent material.
8. When mounting accessories, do not weld across
the flanges.
9. When mounting accessories, do not weld within
19 mm (3/4-inch) of a flange.
10. Do not weld up to the edge of a part being welded
B-09088
to a frame. Leave 6 mm (0.25-inch) between the
end of the weld and the edge of the part.
11. Do not weld cast brackets to the frame.
12. Do
reinforcements and base rails together.
13. Connect the welding machine ground cables as
close to the working area as possible.
14. Avoid direct contact between the welding cables
and any part of the vehicle.
15. Do not get the welding cables near the vehicle
wiring.
not weld the fla n g e s of cracked