Re: 1978 F250 Timing issue
When you reinstall the distributor, you know you have to bring cylinder #1 up to top dead center on it's compression stroke to the crank pointer's alignment with Zero line on the crank damper.
Then place the dist in place so the rotor points to the #1 cylinder in the cap.
In doing this, the dist has to turn the distance of about 1 cap cylinder spacing to seat in the block before settling at the cap positon 1. The cam gear to dist gear engagement forces this to happen. Also the dist shaft has to engage the oil pump drive shaft at the same time to be able to set on the block and clamp down properly in place.
Does it do this?
If so it has to turn when cranking the motor because it geared to front of the cam when in place.
As to the rotor moving about a 1/4" or so, this is the centrifigal advance and is held in place by small springs. The rotor has to move a small amount in relation to the main shaft or the motor gets no timing change vs RPM change.
Next question is has the timing chain jumped teeth on the crank gear.
If yes, the motor either will start and have no power or be hard to start or not start at all.
How to tell: Valve cover off bank 1 and use plug hole in cylinder #1 to determine when the cylinder is up top dead center on compression.
Look at the valves. Are they fully closed for compression AND does the crank pulley mark alighn with the pointer?
If yes, the chain is in proper position, if no the chain has jumped teeth out of position and needs to be replaced with new chain, crank and cam gears.
There is no mistery. Either it is or is not.
Look at the dist gear. It has a spring pin holding it in place. If the gear has moved up the shaft you should see this as a difference in shaft color where it was at before the pin sheared.