The 'E' Type Forum

Maybe someone can tell me whether I got Led Up The Garden Path by a ? well known Jaguar specialist ? a few years ago ?

On the only occasion that anyone other than myself has ever worked on the car, since I bought it 8 or 9 years ago, they fitted an Aldon Igniter ignition module and disconnected the vacuum advance permanently.

The car has always pinked mid-range when applying ambitious throttle openings, but I?ve been too preoccupied with getting other stuff right and just got used to driving it more gently ????.

Now that the other stuff is more or less sorted, it?s about time I sorted the ignition out once and for all.

PS The needles are right, the carbs too, and the engine and exhaust are standard.

Simpler answer: Fit a Megajolt/EDIS assuming you are not too late and can get Ray to build you one: http://etypeuk.com/forum/viewtopic.php?t=437

Ha Ha ! Was wondering how long it would take to flush you out of the woods with that !

Maybe, but in the meantime ...........

rfs1957 wrote:On the only occasion that anyone other than myself has ever worked on the car, since I bought it 8 or 9 years ago, they fitted an Aldon Igniter ignition module and disconnected the vacuum advance permanently.

The car has always pinked mid-range when applying ambitious throttle openings, but I?ve been too preoccupied with getting other stuff right and just got used to driving it more gently.

Are you talking about a 62 3.8 and not a vac retard later distributor? Can't think why anyone would disconnect a working vac advance. If it was broken and lesking air, then yes. Trust they capped the manifold attachment point and you aren't running weak on that carb?

Loosen the distributor clamp and turn the distributor very slightly anticlockwise and retighten. See if it pinks under acceleration in a high gear at lowish revs. If so, repeat and move the dizzie a fraction more each time until it stops pinking. To be truly scientific you should 're-challenge' and put it back to the last setting that caused pinking to see if it reappears. Assuming it does, you settle at the position where it first stopped.

You might have to tweak your idle setting a bit when you're done, if it idles slowly. The vac advance is useful but basically just helps cruise economy and the car should run fine without. It does not contribute to pinking if connected right and working. Make sure the mechanical advance is lubed and free (i.e.snaps back when you twist the cam clockwise against bobweight spring tension.

Three of the best-performing XK engines I've had have been on points. Assuming your Aldon thing is just a points replacement trigger, you already have the no maintenance benefits of electronic ignition and you should be able to get it running fine without a full digital system.

Pete

Pinking suggests an advance problem which is hardly surprising if they have disconnected the vacuum advance and not replaced the dizzy with a mechanical advance version. Start by going back to a standard contact breaker and reconnect the vacuum (if the car has one ). If the problem clears then replace the entire dizzy with a one from here: http://www.simonbbc.com/distributors/6c ... istributor or http://www.simonbbc.com/distributors/6c ... c-ignition

Given the cost it is hardly worth spending time on trying to fix the Aldon!

Heuer wrote:Pinking suggests an advance problem which is hardly surprising if they have disconnected the vacuum advance and not replaced the dizzy with a mechanical advance version.

David, every XK dizzy is a mechanical advance version so that doesn't make sense.

Every dizzy except the US federal cars was also vac advance.

The US cars went to either vac retard or no vac system at all, but they always had mechanical advance. The vac advance is effectively irrelevant to performance or pinking if working correctly, since it is automatically disabled under those conditions that cause pinking.

It only kicks in at light loads/hight vacuum, which is the exact opposite to when pinking is a risk. 'Flooring it' to provoke pinking destroys the vacuum effect and nullifies vac advance (which is always additive to mechanical advance and therefore is presumably why whoever fitted the Aldon mistakenly thought it might help the pinking problem to disconnect.

There are different advance ranges and static timings for vac advance v vac retard or no vac, so a combination of crummy parts and settings could lead to vac disconnection exacerbating mistiming, but on a 62 it's a non issue.

IF the dizzy is knackered then I agree those seventy five quid rebuilds are stunning value, but since fitting one would require the timing to be dialled in as described, it is more work as well as more money to do that than just time the car with its functioning but mis-timed Aldon. If the Aldon were dud the car wouldn't run, presumably. Throwing a new dizzie at a simple ignition timing issue (even a great value dizzie) is like fitting new wheel bearings instead of adjusting the play - you have to follow exactly the same setting procedure with the new bits that you would have done just adjusting the existing parts, except now you've got the extra cost of the replacements and the removal and refitting aggro.

Rory has a '62 so with his comments about being "led up the garden path" and removing the "vacuum advance" (on a '62 3.8) to install the Aldon Igniter I assumed this was going to be a complete botch job, rather than just partial. The Aldon Igniter is a simple replacement for the contact breaker set, similar to the Magnetronic and indeed the Powerspark module fitted in the Simon BBC units, so in itself should not cause the problem Rory is experiencing unless they have somehow installed it incorrectly and it is interfering with the advance or retard movement. There is always the consideration that the dizzy is worn, hence the suggestion of the recon units. It would probably be helpful if Rory could give us the dizzy part number - 22D6, 25D6 or 45D6.

It does make you wonder about the so called 'professionals'. When I test drove a classic Mini my son was interested in, it was running really rough and I mean really rough.
I used it as a bargaining tool to get some money off. When I got it home I couldn't get it running right until I removed the dizzy and found someone had fitted a Powerspark electronic ignition system.
I reset everything and guessed approximately where the dizzy should go before getting the timing gun on it and it was near enough perfect.

Now fitting an electronic ignition to a dizzy is fairly straight forward for a shade tree mechanic but a trained mechanic it should be a walk in the park. I have the original invoice of the work that was carried out and by which garage so I know they fitted it.

Dave

Like Peter, I have over the years been acquainted with quite a few XK engines . Some pink, and some don't ( and if you look at the original E type road tests, you will see that reference is made to a trace of pinking ) . My 9:1 OTS 4.2 has a rather curious pinking habit : it will not pink at low speed under heavy load, but as one opens the throttle at about 1800 rpm it pinks audibly until one reaches about 2/3 throttle when it stops. This suggests that it is not purely an ignition timing related problem but may also result from transient mixture weakness. David Lonsdale, for instance, suggests that this problem results from too light oil being used in the dashpots . My 8:1 FHC however, does not pink and never has done, and I have swapped distributors between cars to see if it altered things. Frankly, bearing in mind that these cars were designed for 100 octane fuel which is no longer available, I think that some pinking is to be expected . Another thought which needs to be considered is this : if the engine is a user of oil, as so many are, this lowers the octane , and thus knock resistance, of the fuel very considerably, and may itself be a cause of pinking even when the engine tune is perfect

Shell V-Power Nitro+ is 99 octane, BP Ultimate is 98 octane and Tesco are supplying Momentum99, the latter having received very favourable reviews compared to the first two. Cheap fuel will certainly cause pinking as I found out when having to use the refinery sweepings on offer at Italian fuel stations but Rory, being in France, has easy access to high octane as it is sold almost everywhere. Could be that simple though Christopher especially if he has been filling up at Carrefour or Leclerc

Heuer wrote: http://www.simonbbc.com/distributors/6c ... istributor

I would avoid these units. I bought one but when tested the advance curve was nothing like the standard distributor. It advanced too quickly and topped out at about 47 degrees of advance at 5000rpm.

Hi Rory ,if you buy a book by Des Hamill ''how to build and power tune distributor type ignition systems'' you will find the info required. Basically the total advance and the rate of advance are adjustable to suit any engines state of tune - just retarding the timing by moving the distributor will stop the pinking but leave the engine hopelessly retarded at other points in the rev range .The E type requires a 13 degree distributor (distributor degrees) which is 26 degrees of crank rotation add on @ 8 - 10 degrees of static timing (ie the setting when the engine is stopped) and the total advance is 34 - 36 degrees - this needs to be checked with a strobe and an accurately marked crank damper. Full advance should be around 3300 rpm .It is a matter of checking and adjusting the advance springs and road testing - should cost you about ?10 in springs and about 40 hours or so of your time ! The vacuum gear is just a light loaded engine advance mechanism to save fuel and only works at closed or only very light throttle - this should be disconnected for testing . Use 97 octane and above fuel.
Hope this helps

regards Barrie

"The vac advance is effectively irrelevant to performance or pinking if working correctly, since it is automatically disabled under those conditions that cause pinking."
I believe this is not 100% correct. I have an EV12 with a 6,0 L motor from a '93 XJ81, equipped with the 4 original stromberg carbs and an ignition sytem from a XJ12 5,3L HE.
If I press the pedal suddenly between 2000 - 3000 rpm, the motor pinks for 1 - 1,5 seconds. I believe, that the "change rate" of the vac advance is too low. Modern fully electronic ignition systems have a very high change rate. Calculated 500 degrees in 1 second. The change rate ( I thinks it is called "attack rate") of an old mechanical system of the vac system is X0 times lower. It takes time. until the vaccum has totally disappeared and the system inside the distributor has moved.
When the filling of the cylinder is rising suddenly, when pressing the pedal fully, it takes 1 second that the vac-advance is reducing to zero. Then pinking can accure, although the system is okay.
Has anyone a better idea ?
Regards Wolfgang Gatza

I agree with Woolfi : see my earlier post about transient pinking on my S2 OTS . The vacuum does take time to subside when the throttle is opened from a high vacuum situation of very light throttle at modest engine speed. The distributor baseplate moves very quickly, but the depression in the manifold requires quite a lot of fluid motion ( i.e. air, which has considerable inertia ) to fill it, particularly in a manifold system as cavernous as a 4.2

The XJ12 serie III with the 5,3 HE-motor would have also this problem, if he would not have a system with some "plastic boxes" in the pipe system between induction system and vacuum box of the distributor.
One of theses "boxes" called "dump valve", shall reduce the vacuum quicker. At my car this is working not very well.
Roger Bywater is explaining this system very well on his site.

http://www.jagweb.com/aj6eng/vacuum.php

Regards Wolfgang Gatza

Right enough. I have owned and worked on quite a few V12s and in all their four different ignition forms: OPUS, Lucas CEI, Marelli and NipponDenso. But these were not being discussed.

I make a distinction (possibly spurious) between ongoing pinking as in climbing a hill or a bout of acceleration lasting more than a second or two, versus an instant of harmless pinking as the mechanicals catch up with fluctuations in manifold depression. The lag happens in both directions of course, but only manifests as pinking when going from high to low vacuum. It is also perfectly true that backing off the distributor to just shy of pinking at max advance does not at all guarantee optimal timing elsewhere in the range as controlled by weights and springs or mapping. It is a perfectly adequate rule of thumb though for standard engines running modern fuel and fitted with the correct distributor - or for working from scratch with a modified engine whilst a fuller work-up is enacted.

I was talking about correctly-configured ported vacuum advance from the front carb on an XK. Manifold vacuum take offs, emissions junk and various iterations of vac retard or capsule-free S2 dizzy display different characteristis but as with the V12s I didn't have those in mind.

Pete

I have mounted correctly-configured ported vacuum advance from the front carb at my V12 6,0. Zero vac at idle, high vac at low throttle and low vac at full throttle.
If I disconnect the vac from the distributor, I don't have pinking , when suddenly pressing the pedal to floor.
I have checked with a vac-gauge, the decline of vac , when pressing the pedal. I think I have seen a time-lag between pressing the pedal und declining of vac. This result is not shure, because I have mounted an extra rubber hose from ported vac at the distributor to the gauge insde the car. The extra amount of air in this hose, which has a lower pressure than atmosphere, ads time to the declining of vac. Maybe without this long hose, the decline would be quicker.
To reduce the problem, I have reduced the amount of advance of my vacuum capsule at the distributor from 24 degree (crank) to roundbaout 16 degree.
Regards Wolfgang Gatza

Wikipedia has an excellent article on knocking at:http://en.wikipedia.org/wiki/Engine_knocking
XK engines are prone to this due to the large combuston chamber and the off center spark plug. On ignition, in a partial vacuum, on partial throttle the flame front travels very slowly (that's why you need additional advance at light throttle at highway cruise rpm, which is provided by the vacuum advance) and the peak pressure point in the combustion chamber will be too late for optium performance. This slow flame front with it's pressure spike also increases the tendency of pockets of fuel on the other side of the cylinder to spontanously ignite (effectivly explode) because the pressure spike increases the temperature in the chamber to that great enough to ignite the fuel before the flame front reaches it, which in turn causes the charteristic resonance in the cylinder wall that we know as pinking/detonation. Ulitimately the cause of this problem, given the octane rating of the fuel that you are using, is too much advance at the lower rpm. I've had to deal with this in my E type race car. It can be a deadly problem as under harder acceleration you may not be able to hear any detonation that may occur over the engine noise. Mild pinking by the way is generally thought to be harmless. If the mechanical advance curve is as specificied by Jaguar then changing the springs to delay full advance to 4000 rpm will probably help but you will need a distributor machine to make that job easy, along with a box of springs. I think that we're all using really old distributors and the springs may be a little tired, allowing eary advance and hopefully that's your total problem.

Took my eye off the thread, all that effort and you'll think I'm not paying attention.

Some great observations here, many thanks.

The distributor is the DMBZ.6A to answer somebody's question.

If I want harder springs, what's my best source, and where can I see what the standard curve look like anyway ?

Given the state of tune of my engine and the use to which I put the car, I'd rather avoid programmable electronics and $$$$$$$ for the time being ; the fastest time I ever set at Paul Ricard was on a 'bike I'd set up with points and a fag-paper when the Lucas Rita packed up in practice ..........

Rory

CMC have their own set of advance springs for high performance engines.They fitted them to mine before I went EDIS. Give them a call.