The roll pin was a different level of hell, probably one of the least pleasurable jobs I've done on the XJS. Broke the tip off of or bent several punches, made no progress with multiple drill bits, and really couldn't get it to go down further than about 1/3rd of the way. Ended up heating it as best I could with the torch, failing to make any further progress while breaking 2 more punches, then giving up and using the air hammer on the backside of the advance to push it out of the distributor body.



(remnants of the vacuum advance)

The air hammer worked a treat, it simply sheared off the rest of the pin, advance body came right out, and I've since installed the new vac advance. Just waiting on a new cap & rotor. Funnily enough, the air hammer vibrations loosened the distributor enough that the top half came free and started to rotate, not that it matters now.

 

Funny how the jobs that are the 'simplest' often become the most challenging - the size of the problem is infinitely proportional to the trouble it causes

 

Inversely?

 

Yep the simpler the job or problem the more complex it ends up being in reality

Smallest electrical issue takes the longest to resolve etc etc - and don't get me started on intermittent problems ... that usually have a simple cause

 

Is the current best practice for the advance plumbing still to just run a line straight to the ported fitting on top of the right throttle assembly?

 

The advance goes via a delay / regulator if I recall not direct to anything but what it does go to depends on region though ultimately it gets to the manifold - pretty sure vacuum is held off the distributor for starting - this is one where you need to refer to Roger Bywater's info and assess what you have, and it may not be identical, don't assume that previous owners have it correct - but don't assume that they don't either.

Edit : Rogers vacuum info

For what it is worth and I don't know how many that visit the Jaguar forums have Rogers documents but they should be on any V12 owners list. Roger has a lot of knowledge re the V12 its versions and development - I would recommend Rogers 'Jaguar V12 Dosier' to all - should be read alongside the Palm XJS bible

 

That works, but the factory vacuum regulator/dump valve set up helps optimize the timing at idle and on throttle opening with no disadvantage (as long as you eliminate the delay solenoid and timer).
If you connect the vacuum advance capsule directly to the port on the top of the manifold, you will have no vacuum advance at idle; with the regulator plumbed correctly, approximately 11” vac will be applied, which results in a better idle and throttle tip in. The dump valve quickly releases the idle vacuum to prevent spark knock with large throttle changes- all in all, a good (albeit complicated) system.
The delay solenoid and timer can be eliminated; they frequently do not function as designed; that was supposed to lock out the vacuum advance and step up the idle to get the catalysts up to temperature quicker.

 

So I should run a line from the vac adv to the dump valve, and then from the dump valve to manifold vacuum? If so, which port on the dump valve goes to which?

My car doesn't have any of the old lines or parts from the old timer system, hasn't for years, but I should have a box with them from an engine I tore down.

 

The regulator port marked “carb” goes to the top of the right manifold, the one marked “dist ” goes to a tee; one leg of tee goes to the vacuum advance, the other to the bottom port of the dump valve. Top port of the dump valve goes to the RH manifold bottom port. Remaining port on the vacuum regulator goes to manifold vacuum (there are 4 ports at the rear of the right manifold, any will work).
In operation, the regulator keeps 11” vacuum on capsule unless the fitting on top of the manifold is higher vacuum than that, or manifold vacuum drops below 11”. Vacuum is “dumped” if the bottom port vacuum exceeds about 20”, which occurs on coast.

 

Just wanted to verify to make sure this was correct, this is how I currently have it set up. Thankfully I had a spare regulator and dump valve in the box of parts.

While I have the fuel rail/balance pipe/etc out, and knowing my heater control valve is seized, seems like a great time to order a new valve and heater hoses while I have access, so it'll be a minute before I put the new cap/rotor on and see how it runs.

 

Anyone have a spare cap/distributor handy and can tell me what the thread type is? I was able to use my welder to remove the last 2 screws for the cap in the distributor but the threads look terrible... So I'd like to tap them back to what they should be.

 

I'm probably just going to run a 10-32 drill and tap through the holes on the distributor for the cap. No clue what they're supposed to be... Definitely smaller than M5x0.8. ~4.8MM diameter, so #12 and #8 machine screws won't fit, yet I also tried both thread pitches (-24 and -32) of #10 (which has a ~4.8MM diameter), and those didn't really thread in more than a few threads before binding either. I'm assuming it might be 3/16 BSF or 2 BA, neither of which I have the tap nor screws for.

 

Not too sure which thread size you are after.
I recall there are some BA threads on the distributor.
Here is info from a Google search, plus a table of sizes.

British Association (BA)

47-1/2 degree thread angle. This is a metric thread system devised by the British for small screws used in components like speedos. Not metric like you might expect, but with diameters determined by a factor proportional to a power of the logarithm to the base 10 of the thread pitch in millimeters.

You'll find lots of BA threads on any British car, but only for fasteners smaller than 1/4". BA fasteners have their own set of spanner sizes. Typically, a set of "Whitworth" sockets will include a OBA (and maybe a 2BA--bigger number = smaller size) socket.

 

2BA would definitely be the closest, explains why a 10-32 screw will go in a few threads before binding.

The question is whether or not to order a 2BA tap and screws from the UK, or grab the 10-32 or M5 here locally in the US.... Which would make it easier to get replacement hardware in the future anyway

 

There is no magic about the 2BA.
I doubt it is used in manufacturing any longer.
40 years ago I had a fair number of the BA taps and fasteners from 8BA upwards
I still have some but never used them in the last 35 years at a guess.

If M5 or 10-32 does the job use it.

 

The screws are M5x0.8. The new cap should come with screws in it, they are usually integral with the cap - at least they are on my 94 with Marelli ignition.

 

Yeah, Marelli must be different then. Tried M5x0.8 on my distributor and it's definitely not that. The spare '89 Marelli cap I have on the shelf is also not M5.

I'm drilling and tapping it to 10-32 this week, good enough to put the old cap back on just so I can move the car out of the garage to replace the radiator.

 

Being Lucas, probably 2BA, which they stuck with for a long time. It’s close to 10-32, but not same.

 

As a final update to the saga:

• The car started and ran and drove, so thankfully nothing was irreparably damaged during the debacle
• The car ran absolutely beautifully, throttle response and power like I've never had before... for about 20 minutes
• After 20 minutes, the car started running worse and worse, and throttle response was terrible with intake backfiring like there was a vacuum leak
• Found a guide on testing the dump valve and determined the diaphragm inside had died, probably being that it was the first time it had been hooked up/functioning for the first time in 25 years

As much as I'd like to keep the partial idle advance, looks like we'll be going with regular ported vacuum. If only the dump valves were still available at reasonably prices like the 10-20 year old forums posts mention.