1985 4.2 XJ6 Series 3 interference engine?
 

Hi All,
Are the 4.2 1985 XJ6 series 3 engines interference engines or not?
I have an interesting head scratching problem with a no start that gets fuel at proper pressure, spark at each plug, and a Noid light blinking (dimly), at each injector connector.
After comparing my running XJ6 to the non-runner I noticed the distributor is approx. 90 degrees out of time when compared to service manual diagram and to the XJ6 that runs. Same 4.2 and same year.
If the distributor is out of time by 90 degrees while I have cranked the engine over have the valves been whacked?

Firstly I dont know if the 4.2 is an interference engine or not. However, just going on basics, moving the distributor (ignition timing) doesnt change the relationship between the valve and the pistons in operation. If you change the position of the camshaft (or the drive breaks) then valves and pistons can meet each other.

Just looking at this thread re valve adjustments on the 4.2 XKE Data - - Jaguar E-Type (XKE) information, articles, photos and register there are a couple of cautionary notes about not rotating the engine or cams during removal until the cams are off the heads and the valves are closed. That would indicate interference will happen if mis-assembled.

It possible for the distributor to be physically mounted in a different orientation as long as you arrange the spark plug leads correctly to meet basic timing and firing order. However, you haven't said if this is a no start that has suddenly occurred or if its a new car/recent overhaul. If you havent seen this car run before the distributor orientation would lead me to want to do a sanity check re basic timing and firing order e.g. find TDC , check rotor orientation, make sure that cylinder one etc.

this may sound silly but check that you have the cams on the correct sides, when my head was machined it came back with the cams reversed and i had a prick of a time working out why it wouldnt run with fuel and correct dissy timing, no valves kissed any pistons. The friend that machined the head had a heart attack at the time it was in his shop and he lost the plot a bit i think, been using him for years and is well trusted, swapped the shafts over and she fied right up but one noisy shim.....

Yeah, Steve is right on.


It probably will not run with the rotor sending spark to the wrong cylinder. But' o'wise no harm.


Now, if one examines the shape of the combustion chamber and the valve location,
one sees the need for perfect cam to crank timing.


The sprocket to cam shaft connection involves a venier. If the teeth get stripped. out goes valve timing and you get a bunch of bent valves. over heating can cause a cam shaft bearing seizure and the venier teeth are the weakest link. Pow.


Long after my 4.2 went 0 in all holes, I figured that out.
In theory, anyway.


Hello lump!!


Carl

It is definitely an 'interference' engine because I bent a valve on mine due to an inlet valve being a bit lazy returning to the closed position. Engine had not run for 18 months. Series 3 engines have bigger inlet valves so lazy valves can have serious consequences; the earlier engines are still interference but may be a bit more tolerant. The inlet valves are the same diameter as used in the D-type racing engines.

Seized distributor caused the no start condition!
 

The engine wouldn't start, and I have been chasing the electrics for longer than I remember. After freshening up the wiring for all components related to the fuel injection system and testing then retesting all the mechanical components I noticed the distributor was out of time by 90 degrees. Consulting the service manual, an '85 XJ6 that runs, and this forum, I figured out that the distributor was the culprit for the no start condition. The distibutor seized internally and would not spin. It seized up, and the engine turning spun it the 90 degrees out of time.
Replaced the distributor, and it started right up like a dream.
Many months of testing and tracing the fuel injection components, and wiring, it all came down to the distributor being bad.

Weird. There's one for the books.

Good work!

Cheers
DD

Ive seen that once before. When we took the distributor apart we found a loose screw rattling around. Looked like the PO had been replacing points and dropped a screw into the distributor. It bounced around over time until it found a place to cause a jam, then bang.