71 LA 340 timings moved!! how?? looking for help

nm9stheham said

Normal slippage is for the timing to retard, not advance. So that makes me think distributor....

Maybe the wiring from the pickup in the distributor got reversed in the electrical fixes. If it was backwards to start with, then the ignition would trigger on the back edge of the trigger pulse, and you would have to advance the cam to get timing to a normal position. Then if this reversed wiring was corrected, now the ignition is firing off of the front edge of the trigger pulse (which is the correct edge) and the timing is considerably advanced.

The other thing is the damper ring slipping as mentioned; it will slip backwards and make the timing look advanced. But that would not make the car un any differently.

And the vacuum advance rod could be jammed up, keeping things far advanced.

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I have been down that road several times and now recognize it almost instantly. When it's firing off the back edge you can set the initial timing ok. But as soon as you rev it up a little, she starts randomly dropping sparks, and the timing light sees the damper marks jumping all over the place from retard to advance, or not there at all, or way up the ring and no index marks visible. This has never happened to me by itself. It was always occurred right after a new pick-up was installed. I cannot imagine a mechanism for this to occur on a good running engine.
If the hold-down is indeed tight (go twist the D to prove it, not the bolt, the housing) then I'll throw in with the guys that talked about the intermediate driveshaft or cam drives,or most especially a thrown advance spring. Basically nuthin else it could be? The crank drives the cam, that drives the intermediate shaft, that drives the D, that times the spark, that's connected to the ankle bone that's connected to the limb-bone, that's......lol, oh sorry, I don't know what came over me just then. Wilma! I need a beer.