“DISTRIBUTOR POSITION ADJUSTMENT: Randy Wilson, still talking about the AJ6 engine: “Jaguar has a special jig for doing this, but it’s not really needed. The whole purpose is to make sure the rotor is pointing to a wire lug no matter what the current computer-chosen timing is. On normal dizzies, the centrifugal advance moves the timing up… but it also advances the rotor by the same amount, as they are attached. No such luxury with the crankfire system.
“First mark the dizzy body directly in line with the #1 and #6 plug wires (note: 1A and 6A on the V12). Then remove the cap. Bring the engine up to TDC, noting which way the rotor turns. When you reach TDC, the rotor should be pointing at one of the two marks. It doesn’t matter which one (why we marked both). Now turn the dizzy body until the mark is just past the trailing edge of the rotor contact. Just past it, not more than a degree or two. In this position, the rotor contact will line up with the wire lug in cap in the timing range of about 5 to 40 degrees before TDC; the operative timing range of the engine.
“If the adjustment is off very far, the results will be subtle. The most likely thing is the rotor and cap will tend to burn a little uneven…biased against the direction of misadjustment. The cap and rotor will “wear out” a little faster. If the misadjustment is extreme… and I’m not sure it’s possible on the AJ6, there will be a misfire at the extreme end of the timing curve as the spark has to jump a pretty large gap inside.
“Next time, mark the position before you remove the distributor. This is one of those rare cases where “close” is good enough.”
Regarding the Marelli on the XJ-S: “Yep, ëtis the same ideas and principles. I’ve never actually had to pull a Marelli distributor, so I can not comment on the exact position. You would mark 1A and 6A… and set things so the rotor sweep-by happened in the 10 to 30+ before range.”