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After loosening the two bolts that hold the distributor clamp in place,I am still unable to rotate distributor ccw. Need to adjust timing for backfire.Vacuum advance is working fine

Some distributor brackets have a short slotted head screw immediately below the distributor body that tightens a clamping arrangement. You may need to get a mirror to see under the dist and around the grease cup. If you find one loosen it. The distributor body should then rotate independently of the two holed bracket that bolts to the block.

G'day bear,
to PackardInfo.

I invite you to include your "49 deluxe 288 in the Packard Vehicle Registry.

Bear:
Ross Miller’s video on the subject has a pretty clear view of the clamp @ 11:10.

youtube.com/watch?v=XiYY11rwjQ6A&t=1227s

or search

Installing a Distributor | Packard Straight 8 | Ross Miller | Speedwell Garage - YouTube

The clamping screw is at six o’clock on the clamp. The intent is to tighten the bolts at 3 & 9 o’clock before the distributor is installed, and then with the horizontal screw loose install the distributor. Timing is then conducted statically or dynamically with a timing light, following which the clamping screw is tightened. On the left side of the clamp is a feature that allows the gauging of small changes to the timing without the use of a timing light. To do this the clamp bolts at 3 & 9 o’clock are loosened just enough to rotate the body of the distributor. The scale on the left indicates the new datum, or bias to the initial adjustment done with the timing light. I’ve been told that such a feature allowed for a timing adjustment to accommodate a low octane fuel. Once the distributor is adjusted the clamp hold down bolts are re-torqued, and if the owner thought that the poor fuel quality situation had passed the distributor timing bias could be returned to the original position. At least that’s the story that was told to me . . . who knows, it could be true. Once you have the distributor out you can remove the bolts, I believe the bolts have a shoulders, and inspect the mechanism. I believe you will find the clamp has limited authority on timing adjustments, and should be installed initially at zero bias.

dp

thank you for the info