Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
1
I have long suggested that one possible fix for the Marelli distributor issues and threat of resulting fires might be to somehow fit two 6-cyl distributors. Just connect each Marelli ignition coil to its own distributor cap, and route the wires from each cap to one bank. The Marelli would continue to handle timing and spark issues, so the 6-cyl distributors could be gutted, the only parts needed are cap and rotor. Choose the right distributors and the caps and rotors could be very cheap.
I just recently discovered that both MSD and Jesel make belt-driven distributors designed to be driven straight off the camshaft. Here’s the Jesel version:
As far as I can tell, these are only offered for V8’s. Still, it offers ideas for how 6-cyl distributors might be fitted to the Jaguar V12. Might even get away with just one, using the original Marelli distributor for the B bank (that side rarely fails). Of course, the Marelli distributor would look silly with every other plug wire hole unoccupied.
Anyhow, at least four ideas come to my mind right off. First idea is two 6-cyl distributors in the vee, one driven directly from the original distributor drive gear and the other driven from the first by one of these cute little drive belts.
Second idea would be to mount the 6-cyl distributors horizontally near the front end of the cam covers, and mount a stub shaft off the front of the cam sprockets and out through a hole made in the covers (with an oil seal) to a drive belt to the distributor.
Third is to forget the drive belt and simply mount the 6-cyl distributors directly to the front of the cam covers.
Fourth idea is to drive both distributors directly from the crank. That would require a 1:2 ratio in drive:driven pulleys and either two sets stacked or one loooong belt with an idler or two.
All these ideas would definitely involve some machining work.
I kinda like this concept (although know that a distributor-less system would be better in lots of ways).
I wonder about a modified cover plate and jack shaft with two distributor drive gears
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
3
That would work, but I expect most machinists would balk at the idea of fabricating that special jackshaft with two gears.
I wonder if the easiest method might be to gut the Marelli distributor and mount 2 pulleys on the shaft, one driving a 6-cyl distributor just forward of the OEM location and another driving a similar distributor just rearward of that location.
Any of those 4 options sounds like a lot of extra mechanical complication. If I was going to expend any money/effort on a new ignition system it would be to switch to the late model style set up with one coil per plug.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
5
I’d still like to know if there are any 6-bangers out there with an electronic distributorless system that are common enough to be scrounged from any junkyard that you could fit two of to the Jaguar V12. With an electronic controller in charge of the advance curves, the fact that the A and B bank would be completely separate would make no difference, their timing would still be the same.
I once bought a very cool looking 6 cylinder Lucas distributor on eBay. Big, side entry cap held in place by 3 chromed Dzus fasteners. Top of cap read “LUCAS COMPETITION”. I figured it was D-Type or Aston Martin. Same form factor as a XK 6 cylinder. Took me months to figure out where it came from. V12 1959 Ferrari 250 GT. Less than 10 that left the factory with Lucas distributors, starters and generators. They used two, one driven from the back of each cam. I paid $50 for it, sold it to a Santa Barbara Ferrari parts specialist for $1,000.
Maybe we want to start petitioning these guys: 123 Ignition I have the early version of their Alfa distributor. Only 16 advance curves to choose from. But the performance is much better, and more predictable than the standard Bosch mechanical system. A USB programable version for the Jag V12 would be awesome.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
14
And a dreadful lot of them are 6-bangers. So how hard would it be to scrounge up two identical EDIS systems from a junkyard and adapt them to the Jaguar V12? You’d need to install a trigger and two pickups at the front damper. Other than that, it should be a matter of just bolting everything down and connecting up the wires, right? Oh, and blanking off the hole where the atrociously expensive Marelli distributor lived.
In theory, it should not be too difficult: I’m unaware of how much space there is, on the front of a V12, for a dual trigger wheel setup.
Surely, somebody, somewhere has done it…?
Im reminded of the dual 12-cylinder distributors of the Phantom III Rolls-Royce!
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
16
I’ve been here since jag-lovers was a mail list hosted at UWA, and I haven’t heard of anyone doing it. I’m basically flabbergasted, you’d think somebody would have cobbled such a system together.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
17
I think you’d only need one trigger wheel, but two pickups 60 degrees apart.
The twin EDIS trick has already been done, years ago, by Philip Lochner. It’s on this forum, if you just look.
It’s also superceded by Megasquirt-3 which can give you an easy distributorless ignition with or without EDIS. You don’t have to fit the fuel side to it if you don’t want to.
There are some pictures in my old photo albums from nearly ten years ago showing this.
EDIT:- if you look at an early v12, it has twin 6 cylinder distributors anyway.
kind regards
Marek
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
20
Cute demo, but all it really does is demonstrate that an ignition system creates a spark. He doesn’t show it mounted on the engine and running the engine.
How do you have a distributorless ignition without EDIS?
