the accuracy of the drawing dimensions, the old facing plates should be used to lay
out the bolt pattern. Twist-off bolts are usually used to retain the facing plates. A
necked down portion of the bolt allows the hex of the bolt to twist off at
predetermined torque value leaving the bolt head flush with the facing plate surface.
The head is then tack welded to the plate to prevent it from backing out.
Once the new plates are installed, a boring bar with a horizontal feeding tool slide
can be used to machine the plates level and parallel to each other. To achieve this,
the installation and alignment of the boring bar is critical. The boring bar must be
plumb and the tool slide feed perpendicular to the boring bar. After machining, the
vertical distance between plates should equal the wicket gate height plus the
recommended amount of clearance between the gates and the plates.
The diameter of the wicket gate bushings should be measured and compared to the
drawing tolerances. When the headcover is installed to check the facing plates, the
wicket gate bushings should also be checked for concentricity and for
perpendicularity to the facing plates. If it was determined that the bushings are worn
beyond the allowable tolerance, the bushings should be removed from the headcover
and bottom ring and the bushing fits checked for concentricity and perpendicularity.
Nonperpendicularity of the bushing and facing plates should have been noted during
preteardown checks of the top and bottom clearances of the wicket gates. If the
bushings are not perpendicular to the facing plates, the clearance measurements
would indicate that the gates are operating at an angle to the plates. Concentricity
can be checked by hanging a single tight wire through the center of the bushings, or
bushing fits, and measuring from the wire to the bushing or fit surfaces. If the
bushings or bushing fits are not concentric or not perpendicular to the facing plates,
the bushings should be replaced and line bored. Procedures for line boring are
discussed in section V, entitled, "Field Machining Procedures." If it is determined
that the fits for the bushings are concentric, new bushings can be installed without
line boring. When this is done, the bushing inner diameter must be slightly larger
than required to compensate for the reduction in diameter that occurs when the
bushing is pressed in place. This can take some experimentation to achieve the
correct installed inner diameter. To facilitate the installation of the bushings, they
should be shrunk by packing in dry ice or storing in a freezer overnight.
In some cases, the top two bushings or bushing fits will be within tolerance for
plumb and perpendicularity, but the bottom bushing will not. In this event, the top
two bushings are replaced without line boring, and the bottom bushing is line bored
concentric to the top two. This simplifies the installation and line boring procedures
The bushing and pins of the wicket gate linkage should be checked against drawing
tolerances. The bushings on the linkage can usually just be pressed in place already
finish machined. As with the wicket gate