THE INTERNATIONAL JAGUAR 'S'-TYPE REGISTER FORUM

I cant see anything in the photos that looks iffy. The only thing I don't like in the engine bay is the adjustment of the PAS pump and the alternator being a bar going between them.

JCS wrote: ↑Sat Jul 27, 2019 10:02 am The only rule is that Orlando is barred from answering.

Charming!

But, yes, I do know what it is.

I don't like where the fire extinguisher is mounted but doubt that is what bothers Norman.

This is driving me mad, keep staring at the photos but cant see anything obviously wrong. Please Norman give us the answer.

I would not have put the HT leads so close to the fuel pipe feed banjo on the front carb ?.
I have run out of idea's !!.
Dave J.

How about the brake fluid reservoir is not clear as to check the fluid level?

Ok Guys,

First we will let Orlando have a chance with the next question on another subject, after this one.

I am not surprised that no one knows the answer, it is one that very few mechanics know, and as years roll by even less people are able to answer.
Even from the 60’s onwards successive engineers have forgotten the lesson. The problem appears not to have been known, at least in automotive circles until the 50’s. Bentley seemed to be unaware when he designed the Lagonda engine subsequently fitted to the Aston Martin DB2, engineers designing the RR V8 scored no better. Surprisingly Jaguar engineers did take action and I well remember the plaited HT leads within the sleeve in the new Mk X’s in 1963. If we dare straighten out the leads we had about 30 secs before we were looking for another job……..but hey today even main agents can sell HT lead organisers obviously they need some education!

The fault in the images is that the HT leads are fitted with the leads running parallel to each other for a considerable distance. This results in induction when unwanted cylinders fire when the leads are paralleled for somewhere exceeding 5 to 6 inches. In fact in this case the problem is so severe that the ignition IS suffering from induction problems. The leads should be crossed over each other, preferable every 6 inch or so.

A few decades ago I attended Technical College for many years and subsequently taught part time in automotive engineering. Throughout that time we used to invite the local technical representative of Champion to bring along their special induction rig to demonstrate HT lead induction. This demonstration was as follows:-

The engine used was a single cylinder test petrol engine rigged up to show this phenomenon in action. It was the single cylinder Caterpillar engine normally used by oil companies as the standard test engine to evaluate oils for piston ring sticking.

The engine had a H.T ignition lead of around six to seven feet long which was cut across at its centre that is the cable had been sliced so that the
lead was in two parts. One section connected to the magneto, one to the sparking plug. The engine was started by holding the two ends close
together, but so that any observer could see the H.T spark jump between the leads. The two sections of lead were then stretched out parallel with each other for about three feet and the cut ends separated. In this situation there was no direct link between the plug and magneto. The engine continued to run, up and down its normal revolution band from idle to full throttle without any misfire, and without a direct H.T lead connection.
When the room lights were turned out, it was equally obvious that no spark was jumping between the leads and the engine was operating only by induction of H.T across the lead. This proved that an engine could be operated, and H.T induction did occur when the H.T leads remained parallel for some distance within an ignition H.T harness.

Many years ago I purchased two cars that had faults that the factories and local dealers could not rectify. One was a 1987 Mini that could not be driven above 55 mph, the other about 1992 was a 1400c Vauxhall Astra with odd misfires. These cars were less than 12 months old and offered at very generous discounts. After looking under the bonnets of both cars, establishing the leads were paralleled, I was parted with my money and soon made my fortune after repositioning the leads.

Take note there is no physical jumping of the spark when this problem exists, the feeling is that the acceleration is being restricted.

I think many of us are more than aware of inductive coupling in parallel wires/conductors. I'm even conscious of it in my Hi End Audio hobby.

There are many methods of ameliorating it ~ the most common/easiest being the twisting of multicore conductors.

Thank you Norman for the answer, I should have spotted that. I wasnt aware the leads are platted in the sleeve as when I got my car the were straight and I dispensed with the sleeve for that reason.

I recently finished my house extension and I was on the backs of the electricians making sure the TV, computer cat 5e and mains cables were not running parallel or in close proximity to each other due to induction. When I worked in telecoms it was something we had to be aware of especially working on thousand pair junction cables that used twisted pairs.

The trouble with questions like that is that they are not defined and really amount to "How long is a piece of string?"

Jaguar's sheath & clamping system from distributor to head conduit ensure that HT leads run parallel on later S Types for much of the distance. As long as the HT cables are copper twisted multicore all should be fine (induction substantially ameliorated between individual cables). My car has the earlier separator ring system that will help with some basic conductors by spacing them.

The moral of the story is to use copper multi twisted core HT cable.

Cars with sheath.


Pics courtesy of Alan Wiedie






Typical E Type.