so had you checked rotor arm first.. you would have saved alot of time...


that keyboard looks as clean.


note to myself.





I must check my rotor arm when car comes back from garage...








I must check my rotor arm when car comes back from garage...



mine does the old misfire sometimes also.. but god knows when plugs were changed..

XJ40S wrote on 05.04.2012 at 08:20:09:


That's an odd statement  - perhaps you could explain how he did that.

Since on an AJ6 engine distributor the rotor arm does not change angular position when the ignition is advanced or retarded by the EMS ECU, how is your advisor going to know where the spark occurs in relation to the rotor angle? He must have pretty good eye-sight if he can see through a hole in the cap when the spark jumps the gap to a plug-lead pick up when the engine is running and note the precise angle of the rotor arm as it does so. 

It is not the same as the old style distributor where you could twist the base plate to replicate the extremes of the advance and retard of the spark generation.

The  setting of the rotor arm in relation to the pick-up for #1 plug lead when#1 cylinder is at TDC on the firing stroke of an AJ6 engine is relatively easy to accomplish. I simply mark on the distributor body the position of the #1 pick-up in the cap before removing it and re-fit the distributor so that the centre line of the rotor arm points directly to it. The 'T' end of the rotor then allows adequate angular shift either side of that centre line to accommodate the advance or retard timing of the spark and the additional rotational adjustment of the distributor body within the range of the slot for the fixing bolt is enough to get that rotor alignment spot on.

I know a mistake that some make is to line up the rotor correctly before pushing the distributor down to locate the drive gear and failing to notice that the spiral-cut gear cause the shaft and hence the rotor to rotate a few degrees to take the rotor out of alignment. BTDT many years ago! 

"That's an odd statement  - perhaps you could explain how he did that."
Mark maximum advance and maximum retard firing angles on the crankshaft pulley for No 1 Cylinder with tipex (white marker). Looking through the top of the sawn off distributor cap make sure that the rotor arm aligns with the pick up for No 1 cylinder at both full advance and full retard positions. By rotating the crankshaft 120 degress at a time (by counting teeth and marking with tipex) the other 5 cyliners are also checked. This method also picks up uneven tooth wear in the distributor drive.
I can't remember for cetain but I suspect I retarded the disributor many years ago when I fitted a retarding bracket for the CPS to suit unleaded. I probably then overlooked to advance the distributor when I changed back to the leaded 5* bracket when I switched to LPG.
Oh by the way Roly, God probably knows nothing about Jag plugs. God rides a Harley as any American will tell you,
Cheers

XJ40S wrote on 05.04.2012 at 22:26:42:


Interesting.

What are the "maximum advance and maximum retard firing angles" on an AJ6 engine????

And, if you mark the position of the #1 (or any other) cylinder plug lead pick-up on the distributor body before you remove the distributor cap, why in God's name would you need to go to the trouble of cutting a hole in the distributor cap and re-fit it to view the position of the rotor arm?

Sounds like a load of BS to me to over-complicate a ridiculously easy procedure - and it is not even April 1st! 

XJ40S wrote on 06.04.2012 at 19:49:36:


Let's get practical here.

What is your reference to those advance and retard figures - chapter and verse? Owners Manual, Factory Service Manual? Readily available to the DIY home mechanic or just a WAG?

Blob of paint? How crude - try a scribed line on the distributor body to show the relative position of the pick-up in the cap for the plug lead.

God? You have something against religion? After all,  it is Good Friday! 

XJ40S wrote on 06.04.2012 at 20:26:09:


Yes, but WHY?? I still regard that suggestion as BS.

XJ40S wrote on 06.04.2012 at 22:12:22:


Well, BS or not, what you suggest is a totally unnecessary procedure to ensure that the rotor arm alignment is correct to allow the EMS ECU to advance and retard the spark to the required extent to ensure optimum operation of the engine under all conditions.

I still look forward to receiving your answer to my question in reply #9 as to the source of those advance and retard numbers you quoted. I have never seen those mentioned in a Jaguar publication, but, assuming they are correct, they seem to indicate a 25º 'spread' from fully advanced to fully retarded.

It so happens that the 'T' on the end of the rotor arm which is about 16mm wide represents an arc of about 25º between the leading edge and the trailing edge of the 'T' passing a point as it rotates. Of course, the plug lead pick-ups in the distributor cap are not a point - they have a flat face about 4mm wide.

Therefore, since the spark if so commanded by the ECU can jump the gap immediately (or even slightly before) the leading edge of the 'T' passes the leading edge of the face of the plug lead pick-up and equally, if so commanded by the ECU, jump the gap immediately (or even slightly after) the trailing edge of the 'T' passes the trailing edge of the face of the plug lead pick-up, the arc through which the rotor travels past the plug lead pick up when a spark can still be transmitted to the plug is more like 38º to 40º.

Clearly with an advance and retard 'spread' at most  of only 25º, the actual positioning of the rotor arm in relation to the plug lead pick-up has significant tolerance - i.e. it does not need to be as precise as you seem to claim. I still maintain that it is sufficient to have the centre line of the rotor arm pointing at the middle of the plug lead pick-up with #1 cylinder at TDC on the firing stroke. That has worked for me every time on AJ6 engines for the past 20-odd years with never a problem.

As a matter of interest I have just checked the distributor on a 150,000 mile AJ6 engine still fitted with its original distributor and rotor arm (Lucas 54404778). The circle described by the outer edge of the 'T' of the rotor arm is 75mm diameter - i.e. the length of the rotor arm from its centre to the outer edge of the 'T' is 37.5mm. The distance between opposing plug lead pick-ups in the cap is 76mm, so there is a 0.5mm gap between the edge of the 'T' and the face of the plug lead pick-up as the rotor arm passes each pick-up. I wonder how that compares with the 'short' Italian jobs you mentioned in reply #8.

[BTW, your mechanics "in their 50s"? They are just kids - I have 20 years more experience than them!      ]