Hello,

I find conflicting information on the proper static timing value for this year and model. 17˚BTDC ( common in posts ), 14˚BTDC, 8˚BTDC?

I was thrilled to find the following diagram in a post here.




XK Engines timing chart

But after reading it I was only more confused. It seems to contradict. Column 2 and 3 both appearing to be valid matches for an 82 US 4.2 but having drastically different static timing values. Anyone know what the main differences in these two years was that called for for 7 degrees difference?

Questions:
Am I correct that my US '82 4.2L Federal XJ6 needs 14˚BTDC static timing?
And what value should I expect for the total centrifugal contribution? At what RPMs?
How about the Vacuum advance's total contribution?

I thought that these would be in the stickied posts but I don't find them.

Anyone have a curve or chart for the centrifugal or vacuum advances?

Thanks,
Paul Skinner

 

Yes, very confusing. I set my 84 Series 3 to 14deg and it ran pretty well and passed SMOG under those conditions.

 

This far on I consider original specs as merely a starting point. Age/wear/degradation of engine and fuel injection, fuel variances, and driving conditions all conspire. Go with 17º. Tweak it a bit downward if you get any pinging/knocking. With a little experimenting you'll find the sweet spot.

Cheers
DD

 

Jaguar did a little tweaking to meeting emissions requirements. Several different advance curves were used over the years....each being only a subtle change from the others.


I've never seen any specs ...in Jaguar literature....regarding the advance curve. They surely exist somewhere. Probably in some Lucas technical archives. I spent hours searching and came up empty handed but that was many years ago. Might be worth another try.

Some Lucas distributors and vac advance units actually have the specs stamped into them....in some sort of arcane encryption. Try searching on some MG and Triumph forums as well, as you might pick up a trail on Lucas distributor specs/data


Cheers
DD

 

I agree that tweaking the setting may be necessary according to the individual engine and its condition / wear. During the rebuild in 2000, mine was set at 12º BTDC which was found to be the sweet spot, and it's been running fine at that ever since.

 

Hi Everyone,

To add to the confusion, I have just recently fitted a 'serviced and curve set for unleaded petrol' Distributor assembly to my 85 Xj6. (Still 45DM6)

Instructions said set timing at 10 deg BTDC.

I haven't had any issues with it and I am getting 20-22 litres per 100km in moderate to heavy around town driving

Just my two bobs worth and observation

Cheers,

Nigel

 

Thanks everyone!

None of this is going to do me a bit of good until I repair or replace the vacuum advance unit. I plugged the line feeding it since it was sucking air.

I read somewhere that there was a chevy part that could be canibalized to repair this, but I can't find that info now. Anyone know what part I'd be looking for? I suppose $88 bucks for a replacement isn't too bad, but I'd be willing to do a repair to hold me over until I get a new one in hand.

Thanks again!

 

Well, my new in box distributor vacuum advance, which I sourced from David at everydayxj.com, is installed. I cleaned the mechanicals and lubricated and exercised the centrifugal advance while I was doing the swap

The timing is set at 14 BTDC as per the sticker on the bonnet. DUH. It was right there the whole time. In my defense, that is one sexy engine! Who would look anywhere else?

It looks like I'm getting 10 more degrees from the vacuum advance at idle. Rev it and centrifugal puts it off the end of the scale at some where around 32 degrees BTDC Max.

Is that reasonable? I'll tell you it feels like a new car. Set the isle down to 700 and adjusted the AFM screw all the way down then open three turns then keep opening slowly until the idle stopped oscillating. Readjust idle speed, readjust AFM. Steady 700 RPM. Smooth idle. Great power and no pinging.

It feels like I'm driving a Jaguar.

I'm thrilled! I'm going to go take a drive.

 

Great to hear. Sounds like you found just the right numbers
for your engine, the available fuel and your driving habits.


A time tested, yet simple ignition that works just
fine when the components are healthy and fine tuned.


Carl

 

Updating this thread because I'm an idiot.

I struggled with the timing on this car because of valve noise that I though was excessive. I though it was originally pinging, and badly, under load. I was wrong.

The front down pipe from the exhaust manifold was not connected properly! Someone had serviced the exhaust for the PO and when the nuts got tight they called it done. But there was a 4-5 mm gap between the clamp and the manifold on the front joint. Just puffing out exhaust and valve noises at me!

I cannot believe that an exhaust leak less than a foot from the exhaust ports would not make more noise! I thought I could hear a bit of exhaust leak, and I thought it might be a crack in the manifold. Thing was damn quiet compared to any leak i've ever heard. fsss fsss fsss ...