Antique Zenith Dial Belt Replacement

by Al & Jim Adams

Figure A (click image for larger view)

Figure B (click image for larger view)

Figure C (click image for larger view)

Figure D (click image for larger view)

Figure E (click image for larger view)

Figure F (click image for larger view)

Tuning mechanisms are among the few moving parts on a radio’s chassis, and it’s not uncommon to find antique radios that require some type of tuner repair. Many such repairs involve nothing more than replacing a dial belt that has failed. The dial belt is generally routed around the tuning shaft pulley and the tuning capacitor pulley, providing a mechanical connection between the user controlled tuner shaft and the radio tuning capacitor and radio dial. These dial belts were usually made of a woven fabric, and were manufactured to length for specific radio makes/models. It was not uncommon for the dial belts to fail, and radio repair shops typically kept a good supply on hand.

Today, the radio hobbyist has a few options for replacing antique radio dial belts. NOS dial belts for many popular radios are still available, although some are becoming increasingly rare. Pre-made reproduction belts or dial belt kits are also available from a few suppliers. The dial belt kits come with an open ended replacement belt that is cut to length, slipped around the pulleys and glued. These work reasonably well. NOS and pre-made reproduction belts are manufactured to the factory length and usually require disassembly of the tuning mechanism for installation. The prospect of undertaking such a repair may seem daunting, but the actual disassembly is not very complicated, and a typical belt replacement can be completed in about an hour.

For this article, a Zenith, chassis #1005, is used to illustrate and explain the steps required to replace a typical dial belt. You will find a few variations from manufacturer to manufacturer, but the repair process is similar for most radios of this vintage. Only a few basic hand tools are required; a small hammer, a 3/16” nut driver, a small flat blade screwdriver and long-nose pliers. Penetrating oil, such as WD-40, and a felt tipped pen will also be useful during this operation.

With the chassis removed, carefully apply penetrating oil to the 5 set screws on the tuning shaft. Using a felt-tipped pen, mark the positions of the pulley and flywheel on the shaft as reference for later installation. Loosen the 5 set screws (Fig. A) securing the pulley, flywheel and volume control collar. Next, position a paper towel to cover the area around the C-clip to avoid losing it in the chassis during removal. Using a flat blade screwdriver and small hammer, carefully remove the C-clip from the rear of the tuning shaft (Fig. B & C). Gently pull the shaft out from the front of the chassis. (NOTE: The outer bushing, washer and inner bushing, located at the rear of the shaft (Fig. D), will fall during this step. Use care not to lose these parts!) As the shaft is slowly removed, carefully slide the flywheel and pulley off the shaft.

With the pulley and flywheel removed, the new dial belt can be placed into position (Fig E). Slide the tuning shaft assembly back into the chassis and slide the pulley and flywheel back onto the shaft (Fig. F). Before sliding the shaft completely in, carefully install the outer bushing, washer and inner bushing (Fig. G). The inner bushing will be loose and may fall, so carefully hold it in position as the shaft assembly is gently pushed completely in. The shaft assembly should completely engage the volume control and volume control collar (Fig. H). Next, install the C-clip into the shaft groove, ahead of the washer (Fig. I) and gently tap it into place. Position the pulley and flywheel back to their original positions and tighten the 5 set screws. Lastly, slide the belt around the pulleys. When properly installed, the belt fit should be snug, and the tuning mechanism should freely rotate with no belt slipping (Fig J).

Al Adams is a long-time antique radio enthusiast and a member of the Michigan Antique Radio Club. He operates Adams Manufacturing Company, manufacturing polyurethane dial belts and other parts for antique radios.

Jim Adams runs the website for Adams Manufacturing Co. (www.AdamsRadio.com).

Figure G (click image for larger view)	Figure H (click image for larger view)
Figure I (click image for larger view)	Figure J (click image for larger view)