Q&A

Jaguar World's technical advice service

Edited by Ray Ingman

Daimler V8 Low-rider

STAR

QUESTION

QFor reasons best known to myself, I would like to lower the suspension of my Daimler 250-V8: not by a vast amount, maybe ½in to 1in. Also, I would rather not lose ride quality or incur vast expense. Can you help? Ray White

ADefinitely a minority interest question, but there is an economic answer! At the front end, your aversion to expense precludes modified replacement springs, these tend to be ‘uprated’ anyway. Removing coils from the existing springs will also increase spring rate (stiffness) and thus affect ride quality. On the Mk 2 (and S-type/420) steel or alloy spacer shims are fitted selectively above and below the spring. Removal of these will lower the vehicle. As a rule of thumb the ride height will decrease by twice the thickness of the deleted shims (i.e. ¼in shimming = ½in lower). To remove these you will need access to a powerful spring compressor, or if not, a local A&E department. There is rather a lot of energy stored in the springs, so they are best released in an orderly fashion and not ricocheting around your body! As an alternative, shims can be interposed between the lower wishbone and the spring pan with the same effect on ride height. It is possible to achieve this by loosening the spring pan bolts and replacing one at a time with longer versions (3/8in UNF high tensile) and the required shims washers. By using this method, spring removal is not required. The rear arrangement is unique to the ‘Mk 1’/Mk 2 range; its quarter elliptical cart springs are clamped in the middle and attached to the live axle at the rear end. Their front-end location allows the fitment of a spacer between the Metalastik pad and the chassis rail, again longer fixing bolts will be required for the clamp. In this case, the ride height variation will be approximately equal to the spacer thickness. In any lowering operation, you must check for sufficient remaining suspension travel or tyre fouling and have the geometry checked and adjusted to suit the revisions.

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V12 spark plug removal

QIn past servicing articles I have read that ‘controlled application of heat’ is an aid to the removal of seized spark plugs in the V12 H.E. engine. Yes, you’ve guessed, I am (or more precisely my engine is) suffering from this affliction –perhaps you could expand on this comment to extract me from a potentially expensive predicament. Nigel Mees

AAs we like to retain our readers, this process comes under the heading of ‘don’t try this at home’. ‘Cold’ removal of a seized/ tight plug usually also results in the unintended removal of the thread in the cylinder head – sometimes recoverable ‘in situ’ with a Heli-Coil insert but often requiring the total detachment of the head to rectify it – hardly a simple job!

The ‘trick’ used in professional workshops is to quickly apply a great deal of heat to the area of the plug seat then gently unscrew the plug a fraction of a turn, retightening and loosening repeatedly to work the plug out. The degree of heat dissipation in the aluminium head means that sometimes the whole process has to be repeated several times, allowing a period of cooling between each attempt as the head’s grip on the plug resumes. In order to get enough heat into the head virtually instantaneously, a fine oxyacetylene flame is required. A home soldering torch will be useless as the heat input will be exceeded by the dissipation.

You will note this method requires a flame in the proximity of fuel lines and other heat sensitive components, therefore suitable precautions MUST be employed. QMy 1979 XJ12 Series 2 will always start from cold. Usually it then runs smoothly and if stopped restarts readily whether warm or at normal operating temperature.

Occasionally however, when it starts from cold it will run roughly with little power available. If stopped it will then not restart even if it has travelled only about two miles and is not yet at normal operating temperature. If it is then left standing for about three quarters of an hour, it will then restart and run smoothly. During the period after stopping, it does not show any sign of attempting to fire. Sometimes when it is running roughly, it also backfires very strongly from the driver’s side bank of cylinders. There is strong spark from the coil at all times so I assume it to be a fuel problem.

There is nothing that I know that predicts whether from a cold start it will run smoothly or roughly. Although, as an additional observation, I believe that as a precursor to troublesome periods, I can hear an increase in fuel pump noise from the boot area. The car can be used sometimes for about seven days without any issues. Then it will have a rough start and difficult restart from the warm event. There is a suggestion that if I do not drive it for a number of days it is more likely to show the above problems. Jim Towns

AAssuming the main inline fuel filter is in good order, first to eliminate would be the two pressure regulators to be found centrally ‘inboard’ on the inlet manifolds. Pressure differentials are possible across the banks allowing the backfire on either side. Picking up (literally) on your clue, the two fuel tanks have nylon mesh pick-up filters at the lowest points in the system. Over a period of time, fine particles of sediment accumulate in the base of the tanks, the high suction effect of the pump draws the particles towards the fine mesh, ‘blinding’ off the filter and restricting the fuel flow and lowering pressure. The pump strains against this restriction and therefore can become noisy and hot – when the engine (and hence pump) stops, the sediment slowly falls away from the filter once more allowing fuel flow, and so the cycle starts again. We suggest total draining and flushing of the tanks, and cleaning or replacement of the filters (Jaguar part number CBC5649). This will require the large brass ‘bungs’ to be removed from the base of the tanks: these are sometimes covered by large plastic grommets which must be prised out of the lower quarter panels to gain access. On a different tack, check the water temperature sensor resistance readings against those detailed in the workshop manual (temperature/resistance). A problem here will move the fuel map from its optimum setting, thus also causing similar symptoms.

XJ12 restarting problem

Our technical experts are ready to give you help and advice on any problem. If your question is a particularly complex one, it may take time to respond, and in some circumstances it may be beyond our resources to do so. In this unlikely event, we will let you know. Please allow up to three months for a response via the magazine. Personal responses can be given, but at our discretion. Fax: (FAO Jaguar World Q&As): +44 (0)1959 541400 Email: jwm.questions@kelsey.co.uk Post (enclosing an SAE): Jaguar World Q&As, Kelsey Publishing Group, PO Box 13, Westerham, Kent TN16 3WT, England.

JW would like to thank Martin Pike of Classic Engineering, (01992 788967) Keith Parrington of Painting Classic Cars (01323 885123) and Tom Lenthall of Tom Lenthall Ltd (0118 9731614) 0e479381-0069-45af-b2a9-c0a37e1e14de 0e479381-0069-45af-b2a9-c0a37e1e14de