Crane XR700 12-slot shutter disk

Recent posts indicate that although the Crane XR700 ignition kit is still available, the new kits that come from FAST (who took over the line from Crane Cams) are not offered for the Jaguar V12 and therefore do not include a12-slot shutter disk. Some have suggested that one could be possible be made using 3-D printing or other technology. Since I have mine apart to replace the optical trigger, I took some photos and measurements:

The parts are laying on grid paper with 1" major markings, 1/8" minor markings.

Here’s another photo at a slightly different alignment with the grid:

Although I don’t believe it’s critical, the hub mounting hole that is approximately opposite to the key is about 19.8 degrees away from the bottom disk slot.

The disk is 3.70" in diameter. There are 12 equally spaced slots, 0.052" wide and 0.180" deep, measured from end radius to outer edge of the disk.

The 3 holes for attachment to the plastic hub are 0.137" diameter. They are equally spaced and measurement between the outer hole edges is 1.355" (i.e., center to center is 1.355 - 0.137). I didn’t do the math to find the radius, but that should be easy enough.

I didn’t measure the 3 large slots, but the approximate dimensions can be read from the grid paper. The purpose of these slots is to allow access to Allen head cap screws that fix the distributor base to the engine top cover, so exact dimensions are not critical.

Hope this helps someone to take on the project.

Ed Sowell
'76 XJ-S

Hi Ed,
I have one of those discs in the coupe, having bought a Crane system back in about 1987.
A good product, still works well.

I bought a spare system in roughly 2000, it was an update ( XR700 ? ) and I accidentally connected 12V to the input terminal and that wrote it off. For that type of product it is very easy to protect inputs against 12V, and I emailed Crane to explain how to do it ( which a 1st year apprentice would know ). They did not think their product needed improving. No surprise the company foundered.

I suspect Crane had a special tool made to press that disc in one hit. It probably got lost.
However, nowadays for small runs that kind of thing is easily and cheaply made with a laser cutting machine.
Laser cutting on aluminium up to 2.0mm is surprisingly accurate.
All you need is an Autocad or similar file. My small company has many chassis components made for electronic instruments using this method. My guess is a cost of US$5 each for 10 items. I would buy one as a spare.

Perhaps FAST do not think the V12 market big enough to bother.

Plan B is to get hold of an HE distributor and use the GM type ignition amp to go with it.

Good to hear from you, Richard.

As you probably remember, I also put my XR700 in many years ago. It recently failed in the driveway. After some diagnostics I concluded it was the optical trigger. Just got a new one yesterday and am in the process of installing it. It my case it’s a big job because I devised a more solid mounting arrangement and perhaps because of that I can’t get it out without removing the rotor, EFI trigger board, and finally the shutter disk. Of course both the rotor and shutter disk hub are so tight it’s tough to get them off. This morning I succeeded removing the rotor by using a heat gun and slide hammer (separately posted here). To get the shutter disk off I first had to drill out the pop rivets to remove it from the hub, then use the slide hammer again to remove the hub!

I’m now about to reassemble. First though, I’ll do a little test. I plan to connect the new optical trigger to the ignition module, turn the ignition, then hold the trigger over the disk and pass a slot over it while watching the test LED on the ignition module (later models have this handy feature). If the trigger and module are OK, the LED should flicker. But maybe you should give me your phone number just in case it doesn’t :grinning:

Ed Sowell
'76 XJ-S

Is that original disk metal? I presume so. If so, laser cutting sounds like just the ticket! If someone comes up with the CAD file necessary, perhaps a limited run is in order. And it’d be great to know if that disk is the only thing you need to make the current FAST product work in the V12.

If anybody still wants to try the 3D printing idea, might I suggest making the disk and the hub together as one piece? Do we feel that the outer rim would have to be too thin to be reliable as a 3D-printed part?

Excellent photos. Might I suggest another idea, though? Lay the disk on a flatbed scanner, lay the graph paper over it, close the lid and scan it. If you do it right, sometimes the results are so good you can take measurements off the image.

1 Like

I’ll try. Maybe I could tape it to the graph paper so as to properly align it with the grid.


We have a small and not so expensive 3D printer in the factory for making production parts.
It is very slow which is no problem for us, and I am sure the more expensive fancy printers are quicker.
I reckon laser cut the disc from aluminium.
Make the plastic mounting fixture from solid bar on a CNC machine.
Actually FAST may have a stock of them, if not a stock of discs.
Machining time would be 2 minutes max. CNC programming could cost US$25 upwards, depending how smart the programmer is.

This is all very hypothetical. I guess the market for V12 retrofit ignition systems is limited to pre HE cars.
How many of them are still running around with Lucas systems and being prospective customers ?

The problem with making that hub from solid stock is that it might have a key built in. Or it might not. You can see the key in the disk itself in the photos, but can’t tell if the hub has the same thing. If it doesn’t, you’re correct, dead simple to make from solid stock, either metal or plastic.

The Lucas HEI doesn’t need this replacement, but the Opus does. You’re right, there probably aren’t that many customers for it. There might be a few Ferrari owners that would like to buy the disk, though!

If the hub doesn’t have a key, it’s not important where the three mounting holes line up. It is important where the key in the disk is relative to the slots. It looks like the key might line up dead center between two slots.

The hub doesn’t have a key slot.

No, the key is not dead center between the slots:

In this photo, the key is at the top and I’ve drawn a radial line through the disk center and the slot to the right of center. It cross the 2" grid mark 0.68 - 0.7" from the vertical radial line. The angle is therefore between arctan(0.68/2) = 18.8 degrees and arctan(0.7/2) = 19.3 degrees.

Kirby, correct me if I’m wrong, but I believe that the angle between the key and the slot doesn’t have to be perfect. It just has to be close enough for the adjuster to get the timing right. Isn’t that right?


When you adjust the timing by turning the distributor body, you’re changing the alignment of the rotor to cap. If you go too far, the spark might start jumping to the wrong terminal at the limits of advance. Right? I think that’s the case.

I wonder if that would happen if you simply installed this disk upside down? Or perhaps you’re supposed to be able to install it upside down if rotor alignment proves to be an issue.

It would seem that somebody at Crane must have gone through some significant research to locate that key and design this disk.

1 Like

The ol’ shadowgraph trick!

The kit has 2 or 3 little sheet metal mounting brackets that can be assembled variously yo position the pickup. There’s also a procedure in the manual that requires a sacrificed cap with a whole cut in it over where the rotor passes the 1A lug. With a timing light, you can see where the rotor tip is relative to the lug when it fires.

Also, you may recall that the base of the distributor is designed to allow tit to be moved and locked down over several degrees. It would seem that would allow for minor mis-positioning of the slot relative to the key. I think my measurements ought to allow the disks to be made good enough.


Per Kirby’s suggestion, here’s the flatbed scanner image:

Hope this is good enough, 'cuz I’m about to but my dizzy back together.

A couple other comments, just in case someone wants to try making these. One, it would really be nice if a couple extra holes were punched to facilitate later removal of the disk/hub assembly. The problem is, just as with the rotor, it’s hard to pull it off the hub when (not if!) you need to at a future date. Pulling up from the edges of the disk risks bending. I found it necessary to drill out the pop rivets so the hub can be pull on directly. Now, if the disk were made with, say, 10-24 body drill size (#11 = 0.191"), right at the outer diameter of the hub sleeve (for want of the correct term), the user could drill and tap corresponding holes in the hub before installation. When it needs to be removed, 10-24 eye screws are screwed in, allowing a slide hammer connection. Since the hub sleeve is 7/8", the radial position of the holes should be (0.875 + 0.191)/2 = 0.533". They should be on a centerline positioned so as to clear the mounting holes and the heads of the pop rivets. About 10 degrees above the horizontal centerline in the first quadrant in the above scanned image would do nicely.

As separate matter, I’d like to point out that I found the Crane optical sensor mounting brackets to be wanting. I devised an alternative, described in my write-up on the conversion at my website:

This has worked very well for many years. Currently, the photos in the write-up are terrible. I’ve now taken some better shots and will eventually put them up at my website. In the meanwhile, if anyone wants them, let me know.


My suggestion, without actually having had the parts in my hands:

Drill and tap 2 holes in the hub as close to the shaft hole in the center as practical. 10-24 might work but I’d probably go with 1/4-20. Drill a pair of holes in the disk itself to match. Then fab a small plate with two holes of the same spacing. Set this plate on TOP of the rotor carrier shaft and install two bolts and snug them up. Then you can simply gradually tighten these two bolts, alternating from one to the other, and draw the disk/hub assembly right off.

It might even work without the little plate, depending on what’s beneath that rotor. If there’s something the end of the screw could land on and push against, you could just do that.

That would work. In fact, I thought about a crossplate between 2 machine screws, but with a threaded center hole for a bolt to be tightened to lift.

But since I have the slide hammer I just put eye screws in the 2 10-24 holes:

I drilled through the flange from the back side so as to be sure to clear the hub sleeve. First drilled 1/8" pilot hole, then #25 drill, the 10-24 tap.

BTW, that 0.020" aluminum is hard stuff. Hard to drill through.


Aluminum isn’t hard to drill, even the really strong alloys. Are you sure it isn’t steel? It looks too thin to be aluminum!

I think your drill bit was dull!

Just checked the one I took off my car last winter and a magnet has no effect on it. Maybe Duralumin?