Distributor set up and general Timing

V12-Engine
1

Hello Everyone,
I have a 1973 5.3L E-type. It is a UK car and fairly original. I have been reading lots of topics lately on carburettor setup, timing and the distributor.

Mainly because I went for a drive the other day, only to be flat bedded with a fuel leak.
My initial thoughts were old fuel hoses, so I ordered them, however when I made a start on the car, I switched the fuel pump on to find the leak but without any luck. I replaced all the hoses regardless (they needed it).

I then thought maybe its a stuck fuel float valve (which I think it was, the paint inside the air filter looked as though it had seen fuel, and a tink black something was found in the float valve).
Anyway I had now decided to overhaul all the carbs, so they had an ultrasonic clean, new gaskets and diaphrams. I reset all the bimetalic strips to be fully open at 60 deg C. I also blanked off the bypass valves with a home made brass gasket.

With a view to putting the carbs back on and setting up, I decided to look in the distributor and see if the retard unit was working. It isn’t and I don’t plan on replacing it, yet? (thoughts). Also the inside of the distributor was filthy, oily at the bottom with black bits?. I have decided to overhaul it.

I set the crank at 1A 12°BTDC and removed the distributor tops (All three screws with the springs broke). Re tapped. The advance mechanism was indeed sticky so have cleaned oiled and set back in place.

I am now onto the initial at least task of setting the larger spring within the advance mechanism.

I have been reading
http://www.pclarkson.plus.com/Ignition1.html
and
http://forum.etypeuk.com/viewtopic.php?t=9665
to try and find values for the advance curve.

I have taken the values from the Lucas distributor 41387 and the values from Mareks notes and overlayed them on a graph.

My confusion:-
I have an 18° advance cam in the distributor which I am thinking would give me a further advance at the crank of 36°. This would be on top of the 12° set at idle. So a total of 48° advance. However both Marek and Lucas seem to give advice to about 36-38° advance at max rpm.

Also from the graphs it seems the secondary spring needs to start working at about 1500-1800rpm?And be at about 6° distributor advance.
So about a third of the cam movement is on the primary spring only, and then both springs for the final two thirds of cam movement. Would this be a good starting point?
The secondary spring on mine currently engages at the final 20% of movement.

Any help would be very much appreciated.

Steve

2

In my XJ-S book there is a discussion with Roger Bywater about the fact that the H.E. engine is timed at 3000 rpm rather than at idle. This is because 3000 rpm is where the timing is critical, and timing it at idle just introduces more variables – which the factory has to deal with by specifying very conservative timing specs. I asked if it wouldn’t also be a good idea to time the pre-H.E. at operating speed rather than idle for the same reason, and he agreed it would be a better idea. So he came up with specs for timing the pre-H.E.:

So, why don’t we adapt the H.E. timing procedure to the pre-H.E.? Roger Bywater: “What you are saying is absolutely correct and setting the timing at low speed before any advance takes effect is just about the worst way of doing it. In all normal operating conditions the advance could in theory be 4 degrees out yet still be within spec. Allowing for wear and tear, not to mention questionable original build quality, the error could easily be more than that.”
Bywater went on to provide at-speed timing specs for all pre-H.E. V12’s:
Carburetted V12’s 35° BTDC @ 4000 RPM
D Jetronic: 33° BTDC @ 4000 RPM
10:1 CR pre-H.E. Digital P 24° BTDC @ 3000 RPM
You just can’t get a better authority than Roger Bywater; he was the guy leaning over a screaming V12 in an engine testing room at Jaguar dialing the advance up and down by hand to develop these advance specs.
Yes, the numbers for the pre-H.E.’s sound like a lot more advance than the H.E.; that’s the nature of the beasts – the H.E. gets less advance from the centrifugal mechanism and more from the vacuum capsule than the pre-H.E.
So here’s the new and improved procedure for timing the pre-H.E. V12: Warm up the engine, disconnect and plug the vacuum advance, rev the engine up a little past the specified RPM and then come back down to it and hold it there, and set the timing to the specified advance.
Of course, one problem is that the scale on the timing plate doesn’t go far enough. So, set the crank at 20° BTDC and paint a new mark on the damper at 0°. Then you can use this new mark to set the timing at the spec minus 20°.

3

Thanks for the advice.

Is it possible to confirm that the 18° cam is correct.

Are my thoughts about the secondary spring starting to take up slack about a third of the allowable cam distance is a good start?

4

I will set the secondary spring to bite after about one third of trhe cam movement.

Will see what happens.