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Jaguar V12 OPUS Distributor

Jaguar V12

Lucas OPUS Distributor

From the introduction of the Jaguar V12 engine in the SIII E-type up to 1982, a Lucas OPUS ignition system was fitted.  This is a problematic system with marginal performance when it's working right; if you have such a system, it is highly recommended that you replace the ignition pickup and amplifier with a Crane Cams system or some other aftermarket system.

Richard Dowling provided this photograph of a modified Lucas OPUS distributor splattered all over his workbench.

The rotor and cap are not shown.

Notice that there are two sets of three mounting bolts in slotted holes.  The baseplate at top left, which holds the shaft, bearing, and gear, is rigidly mounted to the valley cover with three socket-head screws.  The distributor body at top center is then mounted on the baseplate with three slot-head screws with springs around them.  This leaves the body held to the baseplate by springs so it can be turned relative to the baseplate.  There is a vernier adjustment -- not clearly visible in this picture -- used to turn the body on the baseplate to fine tune the timing.  If the vernier is turned all the way to one end of its travel and the timing is still off, the three socket head screws must be loosened and the entire distributor, baseplate and all, turned to put it within range of the vernier adjustment and the socket head screws tightened back down.

The original OPUS system involves a plastic rotor with ferrite inserts, but Dowling has replaced that with the Crane Cams system which uses a slotted disc with an optical sensor.  "The Crane Cams disc is on the RHS and behind it a 3 pin ( Packard or AMP ? ) connector for the photo pickup."  Both the original plastic disc and the Crane Cams item feature slotted holes to allow access to the socket-head bolts below.

Note that the vacuum advance module is actually a vacuum retard module -- the vacuum connection is on the bottom side of the capsule rather than the top side.  Dowling is in Australia, and Australian-spec XJ-S's have a vacuum retard system.  Most other Jaguar V12's have a vacuum advance system.

Note the screw sticking out of the top end of the shaft.  On the OPUS distributors, this screw -- hidden under the rotor -- holds the rotor carrier to the distributor shaft.  Later distributors did away with this screw and used a plastic clip instead -- a clip that normally crumbles to pieces when you're trying to get the distributor apart for overhaul.

This photo shows the centrifugal advance springs quite well.  For some reason people get in here and see two different springs and conclude that somebody messed up somewhere and installed mismatched parts.  Two different springs are needed to provide the advance curve desired.  The left end of the thicker spring is long enough to allow the advance to move some ways (controlled by the thinner spring) before the slack is taken up and the thicker spring gets involved.

Interestingly, the centrifugal advance mechanism is somewhat different on the Lucas CEI system used in the mid 80's.  The centrifugal weights are shaped differently, and appear to operate through a different scheme as well.  The CEI distributor also features a "thingy", a little bushing at the bottom of the rotor carrier, that is not used in the OPUS distributor.

The original oil seal is a funny sort of critter; Dowling found a more standard-looking seal that can be used to replace it.  "On the LHS below the bore of the bottom half of the dizzy body is the original oil seal.  The new seal is to the immediate left of the ball race.

"The vacuum advance drives a moulded phenolic swivel plate, which is pretty fragile and I had to rebuild the LH end of it to take screws for the photo pickup bracket."

You can look at more pictures of a Crane installation in an OPUS distributor at Bernard Embden's site.


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