I was extremely lucky to find a professional mechanic nearby who was also a big 122 fan, having owned one for over 20 years. He remembered that Volvo used to make a complete kit for refurbishing the timing gears. Dick, at Don Beyer Volvo in Falls Church, VA located the kit - Volvo part number 271944 Drive Gear Set. The gear set included steel timing and cam gears, both felt and neoprene seals, cam thrust plate, cam washer that goes behind the thrust plate and two timing gear gaskets (with different bolt patterns).

After installation, the car is running fine again. Thank goodness there was nothing wrong with the engine. All of the noise was being transmitted toward the top via the other timing gears.

The mechanic said that the cam thrust plate that came with the non-OEM steel timing gear kit was not the same thickness as the Volvo thrust plate. He believed that the difference in thickness was the cause of previous tooth failure.

He commented that the gears currently mounted on the car appeared to be installed correctly. These gears were also OEM Volvo steel timing gears but installed with the non-OEM thrust plate. They were making such a racket that I thought the engine was internally damaged.

I am not a machinist but my father left behind a few tools from his first job working in a machine shop, including a micrometer. I got a measurement of .155 inches on the old brass thrust plate. The non-OEM thrust plate measured .153 inches.

Is there any chance that .002 inches in thickness on the cam thrust plate could cause gear misalignment? He said the difference was visible in how the cam washer fit with the thrust plate.

Thanks in advance for any enlightenment,

Joe M in WV