My Chev 400 Ci engine is missing in cylinders 1, 2, 7, 8. I know this because I have headers and can feel which cylinder is hot and which is cold. Since the firing order is 1 8 4 3 6 5 7 2, and looking at the distributor cap I see that all the missing cylinders are in a sequence. The cap and the rotor look good. It's as if the rotor is wobbling closer to the 3 4 5 6 contacts and farther from the 1 2 7 8 contacts, but I don't see or feel any play in the distributor or rotor.
Does anyone have any experience with this condition?

 

It's 10 years or so since I've owned a vehicle with a mechanical rotor, but it sounds like the rotor is off vertically as it rotates paste the contacts. I.e. it's not touching on one side, and is on the other. That would imply either a defect in the way the rotor is made, so that it is sitting off from vertical just slightly on the shaft, or else an issue with the shaft itself being bent to one side slightly. It could still feel tight, but be off.

Its easy to change a rotor, so I would start there...

 

I've ordered a new distributor cap and rotor. I'll try these and if it still misses then I guess I'll get a new distributor.
It's a mystery why this has happened as there's no torque applied to either the rotor or the cap - or the distributor - that should cause it to distort. I marvel at mechanics who can just fix a car as it seems to me there's always something magical lurking deep within that gums up my machines. A gremlin of sorts that must have it's fun before letting me fix the problem.