Re: 1939 Packard Twelve valve noise

Posted by Tim Cole On 2016/8/9 19:58:22

The valve silencer preload adjustment process involves stem grinding.

As mentioned the valve silencer system (used by Packard under license from GM) will make noise given dirt or wear, but the system usually will last over 100,000 miles in a properly maintained engine.

If the guides are worn, valve stems gummy, springs hitting each other that will also cause noise. However, you are correct in checking the bypass as a first step because if that isn't working the system will be starved for oil.

All of the comprehensive inspection and adjustment involves removing the manifolds and cylinder heads. I always used a dial indicator to set the silencer preload with the valve springs removed. It works like this: You place a .056 feeler between the stem and the unloaded silencer and measure the lift on the dial indicator by pushing on the valve face to bottom the silencer. The reading should be between .01 and .026. If it is more than .026 the difference needs to be removed from the stem. If it is less than .01 a longer stem is required to reduce the clearance.

The way they used to fix this was to measure all the clearances and move the valves around to minimize the amount of stem grinding or valve replacement required.