Advise from dizzy experts appreciated

Hello everyone,

Yesterday I opened the distributor of the US specs E-type . I noticed one of the springs of the advance only gets under tension at a later stage (orange signaled in the photo ) . (1) This maybe normal , to have a more steep curve in the beginning but can anyone confirm ?

And is there technical specs for the springs, **(2)**are they the same ?

Also, I have a Pertronix installed by the previous owner. The circular block with the ferrites is shown in the second photo . (3) I wonder if this is the original used by Opus or is part of the Pertronix kit ? And (4) there is a circular plastic foil covering the ferrites but detaching . Is this ring-shaped foil needed ?

Many thanks


The two springs are different, and as you observed the heavier one only engages at high RPM. It’s the combination of these two springs that forms the “knee” in the advance curve.

The disc with ferrites is a feature of the original OPUS ignition. I guess the Pertronix uses the OEM pickup – which is odd, I didn’t think anything used the OPUS pickup.

Unfamiliar with the foil. As long as the ferrites don’t go missing, I think the foil could be omitted.

Many thanks Kirbert very useful . I just cleaned , lubricated and adjusted the ignition to 12 BTDC at 600 rpm.
I think the foil was just part of the original protection , maybe who replaced the rotor just left it there .

Kind regards

Roger Bywater provided a more accurate method of setting the timing; it involved setting it near the peak torque point on the RPM scale rather than at idle, which is “the worst way of doing it.” It’s included in my Book.

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Here, I’ll copy and paste that for ya:

TIMING THE PRE-H.E.: The procedure is described in the ROM, section 86.35.29/7. Basically, you disconnect the vacuum advance, lower the idle to make sure you’re off the bottom of the centrifugal advance curve, and set the timing at 10º BTDC. Much easier than the H.E. procedure!

On the other hand, there’s a very good reason the H.E. went to setting the timing at 3000 RPM instead of at idle. You’re not likely to burn pistons at idle; it is far more important that the timing is correct at highway speeds. The H.E. procedure minimizes the impact of variances in the advance mechanism: If the distributor isn’t quite within tolerances, the timing will still be correct at 3000 and will merely be off at idle instead. Much safer.

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°.

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Keep the foil if it looks like a washer, insulator, spacer, running surface, seal, anything.

Mine only sees 2500 revs at road speed, what should the timing be there.?

Still according to Bywater’s chart.

Thank you all. Kirbert, I recall seeing that reference to setting the advance in your book, particularly relevant to the specificities of the HE . I already had problems putting my head under the car with the engine running at 600 rpm, mind 3000 ! One thing i did is to use a small surveillance camera attached to a wooden stick fixed between the bonnet flange and the front frame, then i can use the timing gun from the side and watch the timing on my phone screen. It kind of works. My Gunson timing gun has an advance scale also making things easier also for higher revs.

Ive just fitted the pertronix ignitor 2 in my XJ12. I had an excellent result with this type of unit in my Interceptor.

The black disc has magnetic rods, not the ferrite used by opus. It is smaller in dia. Mine did not appear to have the foil

It has the disadvantage that there are no access slots in the disc- you have to dismantle it to get to the screws.

For those interested- i left the tacho connection in the ballast, and ran a wire from coil -ve to the other side of the 100ohm resistor. I bypassed the ballast for the connection to the coil +ve

I am interested in the variations of distributor data. My distributor has 18 deg weights, so presumably should give static + 36 at high rpm (vacuum disconnected).

Haynes (which includes xj12, xjs, carbs and d-jet) gives one set of centrif data- viz. No advance below 900, 24 at 2000, 31.5 at 4000, 36 at 6200 (obv crank angle). Sounds about a match for 18 deg weights.

That also lines up pretty well with the pre-he data in the he supplement.

Haynes is a bit confusing as it lists 3 idle 750rpm conditions- viz 4 deg after (Aussie with the vac retard connected- up to 18 deg- probably 14, so 10 btdc with no retard?); The Swedes get zero (no vacuum) - probably a 10 degree more retarded setting?; Rest get 10btdc no vacuum- which makes sense

There is a distributor data document- gives curves for different part numbers, but they are similar (except he). The pre-1976 seem to have 14 deg max dist advance (28 deg crank).

The retard capsule gives 7-9 dist degrees (14-18 crank) and the advance capsule 4 (8).

The upshot seems to be that a pre-he with vac ADVANCE has a huge part throttle advance c/w those with RETARD. 26 degrees!