ab.1.7. Repairing the Center Hub
Source: Unknown
For those with ailing SB-series tuning dials, I hope this will be of some use:
The following is my best attempt at describing how I restored the broken tuning dial on
an otherwise nice Heathkit SB-101. The end result was a super-smooth operating dial
mechanism, that's robust enough to outlive the rest of the radio.
My dial had the aluminum hub completely broken/stripped out of the center of the plastic
dial (the "pocket"), with many pieces of the plastic floating loosely in the dial pocket. And
there were several radial cracks thru the plastic, running from the hub area to the outer
edge of the dial.
I first applied a little gorilla super glue along the cracks (front side on the central
transparent area, rear side on the black outer area with the graduations), then tightened
a 4" stainless hose clamp around the outer edge, closing the cracks where the super
glue had been applied. Let it set for a couple of hours.
I left the hose clamp tightened around the dial circumference, and fit the aluminum hub
back into the center of the dial, adjusted the hose clamp so when the dial and clamp
were laid front-side up on a horizontal surface, the hub was correctly positioned so the
plastic index cursor piece just cleared the steel ring on the dial that's driven by the pinch
drive wheel. The hub should be rotated to a position such that the hex pocket of the set-
screw on the hub is pointing at about "95" on the dial before filling with the J-B Weld, so
you can position/index the dial per the Heathkit instructions, and can tighten the
setscrew with a long hex wrench from the topside of the radio. Make sure that the hose
clamp and the rear of the aluminum hub are supported to maintain their correct relative
positions when laid on the flat surface (front-side "up"). I then removed the transparent
plastic index cursor piece from the aluminum hub (removed snap ring), and carefully
removed the steel ring from the dial (4 "thru" locking tabs).
With the clamp tightened in the correct position and the hub installed in the center of the
dial in the correct axial (in-out), and rotational position previously determined (when the
plastic dial cursor was still installed), and the dial/hub together and placed outer side
"up", I filled the entire dial "cup" surrounding the hub and out to the outer edge of the
"cup" with J-B Weld. Careful not to get that fill so deep that it is higher than the bearing
surface on the hub that supports the plastic index cursor. After letting the J-B Weld cure
for 24 hours, I machined out a 3/4" wide band of the fill around the outer edge of the fill
(dial pocket) just deep enough to allow for clearance for the pinch roller drive wheel.
Servicing Procedures Page 78
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