Réglage avance à l'allumage

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pdi
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Re: Réglage avance à l'allumage

Message par pdi »

Merci mon ami, tu es vraiment plus que d'un grand secours pour beaucoup de TVRistes.
C'est une chance pour le club de te compter parmi nous.

je prends la route cet après midi sous une pluie battante pour rejoindre Zeb pour le Tour du Mont Blanc avec mon fiston pour copilote.

Il pleut vraiment comme vache qui pisse mais demain est annoncé comme bien meilleur.

Zeb va apporter ses câbles d'allumage car il me reste des mini accoup et un des miens ayant un peu fondu contre l'échappement; je le soupçonne d'être à l'origine de ses petits défauts d'allumage. on va donc tester avec le sien.
Le diesel, il ne passera pas par moi
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Re: Réglage avance à l'allumage

Message par papa125 »

René 67 a écrit :Sur la mienne, avec 12° au ralenti j'ai 28° à 3750 trs mais j'ai l'impression qu'il existe quasiment autant d'allumeurs avec des courbes différentes que de voitures.

D'après "la bible", pour une 450 c'est de 32 à 34° à 4 000 trs.

Un arbre à cames plus pointu peut autoriser un peu plus d'avance parce qu'il a généralement un RFA (Retard à la Fermeture de l'Admission) plus important ce qui a un peu le même effet que de diminuer le rapport volumétrique. En fait l'important c'est de ne pas avoir de cliquetis, si tu as l'oreille fine et que tu n'entends rien, c'est bon.
C'est exactement avec cette méthode hautement scientifique que j'ai réglé mon distributeur l'autre jour :D
"Range ma chambre !" et "Equilibrons !" aux éditions Edilivre, droits d'auteur reversés au Shift Project
Après avoir été nommée "Black Hole", ma Chimaera est désormais ma FOLY : Fear Of Losing You...
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Re: Réglage avance à l'allumage

Message par René 67 »

Ils faisaient comment avant les stroboscopes, à votre avis?

Je me souviens que dans la 203 de mon père il y avait un bouton au tableau de bord qui permettait d'ajouter ou d'enlever de l'avance en le tournant.
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Re: Réglage avance à l'allumage

Message par Thunderbolt »

René 67 a écrit :Sur la mienne, avec 12° au ralenti j'ai 28° à 3750 trs mais j'ai l'impression qu'il existe quasiment autant d'allumeurs avec des courbes différentes que de voitures.

D'après "la bible", pour une 450 c'est de 32 à 34° à 4 000 trs.

Un arbre à cames plus pointu peut autoriser un peu plus d'avance parce qu'il a généralement un RFA (Retard à la Fermeture de l'Admission) plus important ce qui a un peu le même effet que de diminuer le rapport volumétrique. En fait l'important c'est de ne pas avoir de cliquetis, si tu as l'oreille fine et que tu n'entends rien, c'est bon.
Steve Heath précise d'ailleurs que les valeurs données ne doivent être prises que comme un "guide".
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Re: Réglage avance à l'allumage

Message par René 67 »

Tout à fait :)

Le hic, c'est quand comme moi on est un peu sourd, (non, non, j'entends déjà les mauvaises langues, ce n'est pas l'age c'est héréditaire) pour détecter le cliquetis ce n'est pas évident et on doit recourir à l'électronique.
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Re: Réglage avance à l'allumage

Message par pdi »

Je vous tiens au courant des suites, d'abord j'ai acheté une lampe stroboscopique, ce qui m'évite de faire 15 bornes pour aller chez mon pote.

Donc réglée à 8°, le moteur tournait bien avec de minimes accoups visible d'ailleurs à la lampe avec un repère qui se déclenche brutalement tous les 5 à 10 secondes le temps d'un éclair. par contre, ça manquait de puissance en haut passé 4000 trm

Réglée à 10,5°, j'ai fais le rallye du Mont Blanc: ralenti OK mais toujours les mêmes accoups et manque de patate au dessus de 4000 mais uniquement par moment mais alors plus net.

Réglée à 12°: ralenti instable et pétouilles encore plus nombreuses en décellération (elle a toujours proutté comme disait mon fils plus jeune :D ). Et manque toujours de patate passé 4000 trm.

Démontage des bougies et nettoyage avec des bougies plutôt sèches.

Remise à 8°: ralenti OK et manque toujours de puissance en haut

Au final, entre 8 et 10°, pas vraiment de différence à part peut être un ralenti plus stable à 8°

Je n'ai pas vu d'étincelle sur le faisceau dans le noir qui témoignerai d'une mauvaise conduction.

Je suis en déplacement pour le travail en UK mais me repenche dès mon retour sur la bobine qui me semble pouvoir être une cause, ainsi que sur les masselotte de l'allumeur qu'on teste en regardant si le doigt peut bouger facilement de 20/25° puis revenir à sa place si j'ai bien lu.

D'autres avis éclairés ???
Le diesel, il ne passera pas par moi
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Re: Réglage avance à l'allumage

Message par René 67 »

Vérifie aussi l'état du doigt d'allumeur et des plots sur la tête d'allumeur, ça peut aussi créer des ratés d'allumage.


Passe à un allumage statique programmable :P
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Re: Réglage avance à l'allumage

Message par pdi »

j'y ai pensé mais tu as les références pour nos moulin?.
Un modèle "simple" m'irai comme sur la Z ou tu en a un avec trois options calme sport et piste et d'autre entièrement programmable mais c'est pas de mon niveau.
Le diesel, il ne passera pas par moi
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Re: Réglage avance à l'allumage

Message par René 67 »

lolo106
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Re: Réglage avance à l'allumage

Message par lolo106 »

Bonne lecture :

How to Power Tune Rover V8 Engines for Road & Track

Chapter 4

Distributors & ignition timing

LUCAS DISTRIBUTORS

Early distributors had single or dual contact breaker points with vacuum advance. While these distributors were efficient they will all have had extensive use by now and will be exhibiting the usual shaft and bush wear. Such wear will cause the engine firing to become erratic as revs rise and the shaft starts gyrating within its bushes.

Any perceptible sideways movement of the distributor shaft is not acceptable for any high performance application, especially a high rpm one. Rather than have the existing distributor rebushed, go to a wrecking yard or a Rover V8 specialist for a replacement without any play between shaft and bush. Distributor bodies can be rebushed, but the shaft may still be worn and so may the cam. Although replacing the bush will often reduce the amount of play by 50%, replacing the worn shaft and the bush of an older points type distributor is seldom considered cost effective given the keen price of brand new aftermarket high performance distributors.

Of the two early versions of the Lucas distributor, the twin point is the better one to have because of its better electrical efficiency at anything above 5000rpm. The later ‘sliding point’ single points distributors, as used in Range Rovers from 1981-1984, have longer lasting points.

Electronic conversion kits are readily available for the 35 D8 distributors from companies such as Lumenition under its part number C FK114 PMA50 CEK150. For details of Lumenition, visit the website at <http://www.lumenition.com>.

The 35 DE8, 35 DM8 and 35 DLM8 Lucas electronic (without contact breakers) distributors can all be fitted with Lumenition conversions. The cost of repairing a Lucas electronic distributor can be quite high, depending on how much work is involved in the rebuild. The spark intensity of a standard Lucas electronic distributor is quite sufficient for any application, including racing use up to 7000rpm, and many engine builders stay with the Lucas distributor for all applications. The Lumenition conversion kits for the 35 DE8, 35 DM8 and 35 DLM8 distributors are part numbers C FK110, PMA150 and CEK150.

Make sure that you quote the Lucas distributor type when ordering a Lumenition conversion kit so that you get the right pickup. The basic electronics in the two kits are identical, but the attachment of the pickup in a contact breaker points-type and an electronic distributor is different!

Repair

Most readers will find that their skills and available facilities will limit the repairs and modifications that they can make to any of these distributors. Most of the ‘repair’ work will be making sure that all of the components used are serviceable, such as the distributor cap, points, condenser, rotor arm, electronic module, vacuum advance canister, coil, ignition leads and sparkplugs. The spark intensity can be checked at the end of each sparkplug lead (wire) by using a tester, such as a Snap-On MT 2700 inductive pickup tool or a Gunson ‘Flashtest’. The module will need to be checked by an auto-electrician/automotive parts supplier for uniform output.

Mechanical advance system

All Lucas distributors fitted to Rover V8s have a mechanical advance mechanism which automatically advances the ignition timing via the centrifugal action of two interlinked bob-weights. These bob-weights are located inside the distributor, under the contact breaker points baseplate or electronic pickup plate. As the distributor shaft rotates, the advance mechanism’s bob-weights move outwards from their at rest position. This movement rotates the eight-sided cam in relation to the distributor shaft, a process which advances the ignition timing.

The mechanical advance mechanism (or ‘centrifugal advance’ mechanism as it is sometimes known) has a built-in limit as to how much advance can be provided. The maximum amount of centrifugal advance is pre-set by the factory and is not designed to be altered.

Most Rover V8 distributors have a maximum 11 degrees of mechanical advance built in, which equates to 22 degrees of crankshaft advance (the crankshaft turns at twice the speed of the camshaft). Ignition advance is always measured in crankshaft degrees: never in actual distributor degrees because it’s more convenient and logical to relate the firing point to the crankshaft position and hence to the piston crown position.

Another aspect of the mechanical advance mechanism is the rate at which the ignition timing advances from the static/idle speed setting. The rate of the advance is controlled by two small springs which control the movement of the bob-weights. A standard Rover V8 will idle at about 800rpm and, at this speed, the mechanical advance will not be operating because the advance springs are strong enough to prevent movement of the bob-weights. The springs allow the advance to start at about 1000rpm and full advance will be achieved at about 4500rpm.

Changing static advance setting

The factory static/idle speed advance settings range from 2 to 6 degrees BTDC, which is very low. Most engines will respond to the advance being increased to between 10 and 16 degrees, depending on the engine’s capacity and its state of tune.

Take a standard SD1 3.5 engine fitted with a Lucas 35 DEM distributor as an example. If this is set with the standard recommended static/idle speed advance of 6 degrees before top dead centre (BTDC) and it has the usual 22 degrees of mechanical advance built into these distributors, then there is going to be 28 degrees of total advance registering at about 4500rpm and above.

A significant improvement can be made to the performance by simply advancing the ignition timing so that there is 12 to 14 degrees of static/idle speed advance and, hence, 34 to 36 degrees of total advance. Not only will the engine perform much better, it will have a lower fuel consumption during normal running. The only drawback is that the engine will be less tolerant to labouring in a high gear without ‘pinking’ (‘pinging’). This is no problem for most of us who would naturally change down a gear anyway. Heavy cars with automatic transmission might not be able to stand 14 degrees of static timing, but 12 degrees should be acceptable.

Remember! – always disconnect the vacuum advance pipe whenever ignition timing is being measured by a stroboscope.

Changing the rate of advance

Changing the stronger advance spring of the two for a weaker one will allow the mechanical advance mechanism to advance quicker, which usually equates to quicker engine acceleration. A suitable light spring is the lighter spring of the two fitted to the X-Flow (1300cc/1600cc ‘Kent’ engine from the 60s and 70s) Ford Motorcraft distributor which will reduce the point of total advance to 3300-3500rpm (as opposed to the standard 4500rpm). The rpm point can be quickly and easily checked with a stroboscopic ignition timing light once the crankshaft pulley/damper has had the appropriate extra timing marks added to it.

Check with a stroboscope the rpm point of maximum mechanical advance with the two standard springs fitted, then carry out an acceleration test over a measured distance against the clock. Replace the stronger standard Lucas spring with the weaker of the X-Flow Ford distributor’s springs. Check again with a stroboscope the rpm point of maximum ignition advance and then repeat the acceleration test of the car. Compare the results.

A whole series of similar tests needs to be carried out using a range of springs which are progressively weaker than the standard stronger spring in order to identify the optimum rpm point of maximum mechanical advance. You should be looking at a range from the standard 4500rpm down to 2750rpm, in 250rpm steps. There are many advance springs from other types/makes of distributors that can be tried, as well as those from other Lucas Rover V8 distributors.

Vacuum advance system

The vacuum advance mechanism is designed to advance the ignition timing under low load conditions in order to save fuel, which is why all road going engines have them fitted. An engine doesn’t create any significant manifold vacuum when the throttles are wide open and the engine is accelerating. An engine does create manifold vacuum when the engine isn’t under high loads, such as when cruising along with the accelerator pedal just into its travel. Under such conditions the fuel consumption is improved significantly by the vacuum advance system.

The amount of vacuum advance can be anything from 1 to 15 degrees in addition to the mechanical advance, resulting in up to 35-50 degrees of total advance. The advance mechanism is activated when there is between about 3-4in Hg and 15in Hg of vacuum in the manifold.

If you are concerned about fuel economy, it can be checked quite easily and with extreme accuracy. If you think your engine is running with too much advance under cruise conditions, fill the fuel tank to the brim and then test the car over a piece of motorway (freeway), driving the car as you normally do there and back over about 20 miles/32km. Fill the car’s fuel tank to the brim again, noting the precise distance covered and the amount of fuel used. Reduce the static ignition timing 5 degrees and repeat the test, then compare the results. A series of such tests may be necessary to find the optimum advance setting for the best economy with acceptable performance, and it’s possible this might involve limiting the vacuum advance by modifying the distributor to limit the travel.

An engine used on the road without a vacuum advance will use on average about 10% more fuel for no gain in engine performance. It’s worth checking the vacuum advance mechanism twice a year to make sure it’s functioning correctly, with no leaks. Vacuum canisters have rubber diaphragms that do perish over time, so a new canister should be fitted whenever a distributor is being rebuilt. Any sudden loss in fuel economy should always send you straight to the vacuum advance mechanism. Start by checking the vacuum tube for leaks and then check the diaphragm to make sure that engine vacuum is translating into movement of the contact breaker points baseplate. With the distributor cap off, disconnect the vacuum pipe from the engine and suck as hard as you can on the vacuum pipe. This is usually enough to detect either a leak in the diaphragm or see movement in the points plate/pick up plate. If you can’t see any movement, something is wrong.

Caution! – Some Lucas distributors are specifically designed for use with SU or Zenith carburettors. If you’re using one of these in conjunction with another type of carburettor and inlet manifold, then be careful. The Lucas distributor’s vacuum advance is calibrated to accept vacuum from a specific position within the carburettor, which is much less than inlet manifold vacuum. The result will be the distributor on maximum vacuum advance at idle and the engine likely to be misfiring at idle.

Racing engines

Any Lucas distributor can be altered to suit any Rover V8 in any state of tune and to match anything else on the market. Many race engine builders use little else because the Lucas distributor has proved to be very reliable to 7000rpm and beyond. The only shortcoming is that the amount of mechanical advance cannot be altered easily, and not everybody is able to do it. The alternatives follow!

VACUUM ADVANCE ON RACING ENGINES

On racing engines the vacuum advance mechanism serves no useful purpose because the engine spends most of its life on full throttle. Caution! – The vacuum advance should be removed from a racing engine’s distributor in case the mechanism fails and remains in the fully advanced position. In these circumstances the engine could end up running with 10-15 degrees of excessive total advance and catastrophic engine damage is highly likely.

When an original equipment Lucas distributor is going to be used for racing, the advance plate will need to be permanently fixed in the non-advanced position. This is usually done by spot brazing or MIG welding the two plates together in the non-vacuum advanced position. The vacuum canister is removed from the distributor body and, if applicable, the slot covered by a plate made out of 16-gauge aluminium to keep out dirt. This plate can be held in place using the redundant screws and screw holes in the body of the distributor that held the vacuum canister in place. Caution! – Don’t forget to block the vacuum take-off point on the manifold or carburettor.

MALLORY DISTRIBUTORS

A very popular alternative to the standard Lucas distributor is the US-made Mallory distributor. Mallory has been making electrical equipment for decades, and it’s of excellent quality and represents good value for money. The website www.mrgasket.com lists the whole range of Mallory ignition equipment for the Rover V8. Mallory makes several distributors for the Buick/Oldsmobile 215ci V8 from the early 1960s and they’re listed below with their part numbers (P/N) –

P/N 2564301 – Dual Point distributor (no vacuum advance)

P/N 2664301 – Dual Point distributor (with mechanical tachometer drive)

P/N 2764301 – Dual Point distributor (with vacuum advance)

P/N 3764301 – Unilite Electronic distributor (no vacuum advance)

P/N 3864301 – Unilite Electronic distributor (with a tachometer drive)

P/N 4764301 – Unilite Electronic distributor (with vacuum advance)

P/N 5064301 – Magnetic Breaker-less distributor (no vacuum advance)

P/N 5764301 – Magnetic Breaker-less distributor (with vacuum advance)

These are all ‘drop in’ fits for pre-1976 Rover oil pumps/front covers. Most Rover V8 specialist companies buy these Buick/Oldsmobile distributors because they’re cheaper than those made specifically for the Rover with straight spade or tooth drives. They will also fit the later 1976-1993 front covers, with some slight alteration, so that they only have to stock one series of this distributor.

The distributors intended for the Buick/Oldsmobile engine have a long shaft with the end machined with a ‘spade’ or ‘tooth’ drive to suit any early-type oil/pump front cover. This means that it can be used on any 1976-1993 front cover by cutting the shaft to the correct length and then drilling and reaming a new hole in the shaft Caution! – a jig is required to ensure the gear is positioned correctly. All that’s required then is a post 1976 Rover distributor flexible (‘wobble’) drive.

These same distributors will also fit all ‘interim’ front covers without any modification. They’re all fitted with drive gears which can be used with the ‘early’ and ‘interim’ engine camshaft gears.

The use of a Mallory dual points distributor should include the company’s Promaster ignition coil (P/N 28720) or the Voltmaster Mark II ignition coil (was P/N 28675), which are the recommended companions for these types of distributors. These two coils are compatible with contact breaker points type distributors because they are high voltage, but not high energy like those used with electronic distributors. The dual points distributors are not designed to carry high current. If necessary use Mallory’s ballast resistor (P/N 700) with both of these coils, and the company’s plated copper core ‘Super Wire’ high tension leads for the distributor. Note that the Mallory non-points type distributors use a high energy Promaster ignition coil listed under P/N 29440 or P/N29216.

Repairing

Generally, It’s better to buy a brand new distributor just to ensure that everything is in perfect condition rather than buy a second-hand one and rebuild it. If you buy a second-hand item or your original distributor gets damaged and you do want to rebuild it, Mallory sells a very comprehensive rebuild kit.

How dual points work

The ‘dual points’ system has two sets of points, one set opens the low tension circuit and the other set closes the circuit within 2 or 3 degrees of distributor rotation. Single points systems open and close within 10 or 12 degrees of distributor rotation. The benefit of the dual points system is that it allows the coil more time to build up its voltage before the next ignition firing. The Mallory ‘dual points’ distributor is one of the best contact breaker points type ignition systems available, and is ideally suited for use on the Rover V8 up to 7000rpm. Use at high rpm relies on the points, condenser, cap, HT leads (wires), rotor and coil being in perfect condition.

Dual points reliability

For those who prefer to stay with technology that they understand and can fix themselves, rather than use electronic distributors, ‘dual point’ ignition systems are very cost effective and efficient. After all, the world used contact breaker points systems for 75 years. They are very reliable if the points used are Mallory or of equivalent quality, and the condenser is of the correct capacity and in a good serviceable condition.

The contact breaker points are the Achilles heel of this type of distributor, as everybody knows, and they will wear out eventually. In most racing use substantial wear will take quite a while because of the low mileage covered in a racing season. It’s unlikely that the points will even need adjusting within 2000 racing miles let alone need to be replaced. Points life on a road going engine will be very good, in fact vastly superior to most conventional points systems. Mallory contact breaker point sets are top quality, which is why they’re relatively expensive.

Adjustable mechanical advance

A near unique feature of many Mallory distributors is their adjustable mechanical advance mechanism, and it’s a big part of their attraction. Other distributors require permanent modifications to alter the mechanical advance, involving specialist facilities. The Mallory distributor enables the optimum static/idle advance and the optimum total advance to be established in testing, after which a simple adjustment sets the exact amount of mechanical advance that’s required.

For example, if your engine requires 16 degrees of static/idle advance and 34 crankshaft degrees of total advance, 18 crankshaft degrees advance will need to be built into the distributor. If your standard Lucas distributor has 22 degrees of mechanical advance built in, then you’re going to have to compromise somewhere. There are three options: set the distributor for 34 degrees of total advance and run 12 degrees of static/idle advance, set the distributor for 16 degrees of static/idle advance and run 38 degrees of total advance, or set the distributor with a split around the optimum timing point such as 14 degrees of static/idle advance and 36 degrees of total advance. The engine will run well, but not quite as well as when everything is optimised, as it can be with a Mallory distributor.

Changing amount of static advance

On YL models the mechanical advance is altered by first removing the contact breaker points baseplate from the distributor body. With the plate out, the length of the two slots is checked using the plastic ‘key’ that Mallory supplies with all new distributors. Both slots should always be exactly the same length. Each flat of the key has numbers adjacent to it that are the crankshaft degrees of advance. The advance is changed by altering the slot length. Undo each securing screw in turn and position the plastic key in the slot with the appropriate flat in contact with the end of the slot and the moveable stop, then tighten the securing screw. Set the other slot in exactly the same way. Both of the securing screws must be tight. Finally re-check each slot length with the key just to make sure that it’s set correctly. It’s as simple as that!

Changing rate of ignition advance

The Mallory range of distributors frequently have the right rate of advance built into them by the factory. On average they’re set to be fully advanced at 2700rpm, but if this is too quick the advance springs can be changed for stronger ones to reduce the rate of advance. All Mallory rebuild kits come with a full range of advance springs, or the springs can be bought in a separate pack. Other aftermarket advance springs can also be used. Stronger advance springs can be used in any combination, allowing any advance rate to be built into a distributor up to, but not exceeding, 4000rpm. Generally, the ignition needs to be fully advanced between 2700-4000rpm. Reducing the full advance point to below 2700rpm is possible, but it’s not recommended because it usually tends to make the engine ‘knock’ or ‘kick back’ under acceleration. It’s not unknown for engines to run perfectly acceptably with the ignition fully advanced by 2500rpm, but this is the absolute earliest that should be set.

The ignition should advance from the static/idle position to the totally advanced position at a rate that causes the engine to accelerate as quickly as possible, but not so quickly that the engine hesitates or ‘pinks’ (‘pings’). This ideal setting is quite easy to achieve through straightforward acceleration testing. Start with the ignition set to be totally advanced at 3750rpm and test the vehicle’s acceleration rate over a set distance. Then reduce the total setting down to, say, 3500rpm and repeat the test, continuing downward in 200-250rpm steps until the optimum advance for the particular engine is reached. It’s best to start high and go down to avoid damaging the engine.

Once the total advance has been set in this way the engine will give its best overall performance. Setting the advance in this way takes time, but it only has to be done once and it can mean the difference between optimum street performance and even winning or losing races. It’s always the simple things that make one car’s performance stand out from another similar car, and, clearly, it often has nothing to do with money.

Road cars

Vacuum advance is required for all road-going engines to provide good fuel economy. All of the appropriate Mallory distributors have this feature as an option.

Racing

At race meetings, always have on hand two spare sets of genuine Mallory points, a distributor cap and a rotor. While Mallory parts are top quality, failure is always possible through the rigours of racing and it’s best to be prepared for the worst. Points, caps and rotors do fail from time to time and getting replacement parts might prove difficult when you need them in a desperate hurry.

Conclusion

Chose with confidence from the Mallory range of distributors with the full knowledge that they do exactly as claimed by this well respected manufacturer. Any Lucas distributor can without doubt be altered to suit any Rover V8 engine’s state of tune; it’s just that it usually involves some fairly difficult modification to achieve an optimum result. When you buy a new Mallory distributor every single component is new and all the required tuning/timing alterations are via simple built-in adjustments. This all adds up to making the Mallory distributor a very reasonably priced and user-friendly piece of equipment.

True TDC

Top dead centre (known as TDC) must be checked to make sure that the crankshaft pulley (damper) markings are absolutely accurate. This is a critical datum for the engine and it’s ignition system: don’t assume that Rover got it right.

There are several ways of checking TDC accurately, but an ideal time is when the cylinder heads are off because a dial test indicator can then be positioned over the crown of number 1 piston. Turning the crankshaft clockwise, the piston is brought slowly up to the top of the bore and stopped the instant that the dial needle reaches its peak. The dial is then zeroed, the crankshaft turned back about a half a turn and then brought slowly back up to TDC. As soon as the needle gets to the zero, stop rotating the crankshaft and mark the damper in relation to the pointer. Continue rotating the crankshaft slowly until the needle just starts to move, and stop rotating the crankshaft. Mark this second position of the damper in relation to the pointer. The midway point between the two marks you have just made on the pulley rim is true TDC.

There are other ways of checking TDC when the engine is assembled: you can use a probe down through the sparkplug hole of number 1 cylinder or an old sparkplug with an extension welded on the end of it to act as a dead stop. In the latter case, rotate the crank in both directions until the piston is stopped by the device and mark the crankshaft pulley: TDC is the mid point between both marked positions. Clearly it isn’t as easy to check TDC with the cylinder heads in place, but it’s still possible and necessary.

DEGREE MARKING the crankshaft pulley RIM

Once TDC has been accurately established and marked on the crankshaft pulley, the remainder of the timing markings can be placed on the pulley rim using TDC as the datum. These additional marks should include static/idle and total advance. The following list includes all the degree marks required to cater for all known advance regimes relevant to the Rover V8.

3.5-litre – 10, 12, 14, 16, 18, 34, 36, 38, 40 degrees BTDC

3.9-litre – 10, 12, 14, 16, 18, 32, 34, 36, 38 degrees BTDC

4.2-litre – 10, 12, 14, 16, 18, 30, 32, 34, 36 degrees BTDC

4.5-litre – 10, 12, 14, 16, 18, 28, 30, 32, 34 degrees BTDC

It’s also a good idea to add the camshaft full lift inlet timing point to help in any camshaft timing. If your camshaft is full lift timed at 108 degrees after top dead centre (ATDC) for example, the damper should be clearly marked at 108 degrees ATDC, and so should 104, 106, 110 and 112-degree ATDC to assist in checking and adjusting.

IGNITION ADVANCE

While each individual engine will need to be tested to establish the amount of total advance that produces maximum torque and maximum bhp, the following settings will be suitable for 98% of engines.

The static/idle advance for all engines will vary between 10 and 16 degrees BTDC, with the smaller engines requiring slightly more than the larger ones. For example, 3.5-litre engines are likely to require 14-16 degrees, while 4.5-litre and larger engines are likely to require 10-12 degrees. You’ll need to experiment a bit here and find the least amount of advance that causes the engine to idle as smoothly as possible with the highest rpm. For example, if 14 and 16 degrees of advance produce equal idle smoothness, but there is no increase in engine rpm between 14 and 16 degrees, then set it at 14 degrees.

As a guide, the chart below sets out the total mechanical advance that can be used on the various capacity engines and that will be correct for 98% of them –

3.5-litre – 36 degrees of total advance.

3.9-litre – 34 degrees of total advance.

4.2-litre – 30 degrees of total advance.

4.5 litre, or more – 28 degrees of total advance.

To set the absolute optimum total advance for your individual engine will mean having it dyno-tested on a rolling road. Before setting the ignition advance the air/fuel ratio needs to be checked to make sure that it’s not too lean or rich, noting that this is not the final setting. The air/fuel ratio at maximum torque and maximum rpm should be in the range 12.5:1 to 11.8:1, which translates into 0.85 Lambda or 5.0% CO.

Next take a power reading with the engine set at the suggested total advance for the engine capacity (eg: 36 degrees for a 3.5-litre unit). This result will give you a baseline reading. Now the total advance can be increased by 1 degree and the engine tested again. If the maximum torque increases, increase the ignition advance by 1 more degree, and continue until peak torque is achieved. Any adjustment to the suggested total advance figure is likely to be slight.

Maximum torque is produced at maximum volumetric efficiency, which means maximum cylinder filling. If too much ignition advance is used the engine will ‘knock’. If your engine’s compression ratio is too high it will not cope with the suggested total advance, and either the octane rating of the fuel will have to be increased or the compression ratio will have to be reduced.

Mechanical conditions aside, obtaining the correct air/fuel ratio and the correct amount of total advance are inextricably linked to achieving the maximum torque and the maximum power possible for any engine. Once the amount of total advance has been finalised the mixture will very likely need to be altered slightly to achieve maximum torque and maximum power.

STROBOSCOPE IGNITION TIMING

It’s important to always use a stroboscopic ignition timing light when setting the ignition timing, which means having a clearly marked crankshaft damper with the correct range of degree markings for the particular engine.

It is essential to check the total advance as well as the static/idle timing. A huge number of people spend a lot of time setting the standard static/idle advance, while giving little thought to the total advance requirements of their engine. This can mean losing anywhere between 10-100bhp on a Rover V8, all for the sake of a little bit of preparation work and something as simple as undoing the distributor’s securing bolt and altering its position.

In fact, total advance figures have rarely been published by car/engine manufacturers over the years, which is a pity because the lack of this information has caused a massive amount of confusion and loss of achievable power.

The optimum total advance ignition timing figures available today have come from race engine builders who have extensively dyno-tested these engines in the quest to obtain maximum power.

When you look at the very conservative nature of recommended standard ignition timing settings you could be forgiven for wondering what the engineers were thinking of when they were calibrating these engines in their laboratories. Well, it’s all quite easy to explain. Engine manufacturers have to produce engines that do everything that might be required of them by all manner of drivers. This could mean having to go up a hill in top gear with the engine labouring away and about to stop, which is something most of us would never ever do. The engines leave the factory being able to cater for an unbelievably wide range of abuse. Electronics have changed this to a degree because they can adapt to a given situation but a mechanical advance distributor can’t cope with the wide range of operating conditions in the same way that an engine management system can.

When you set your engine to the type of ignition regime listed in this book you are individualising your engine’s ignition system for optimum performance without compromise. This means the engine might not be able to cope too well with outrageous situations such as gross labouring under extremely high loadings. If you are not prepared to accept this limitation, you should stay with the standard ignition settings.

Important! – The vacuum advance tube must always be removed from the distributor when a stroboscope is used to identify and set the idle speed and total advance settings. Failure to do this will usually lead to an engine running with too much advance when under load and this causes a loss of engine performance.

TOO MUCH COMPRESSION

If an engine has too much compression ratio (CR) for the octane rating of the fuel being used it will not be able to use the correct amount of ignition advance. The correct solution is to reduce the compression ratio, but many people don’t do this and reduce the ignition advance just enough to prevent ‘pinking’ (‘pinging’). Engine efficiency is lost when this compromise is made. It’s better to have slightly less compression ratio and be able to use full throttle under all circumstances than it is to have an engine that is slightly over compressed and have to use reduced throttle to avoid ‘pinking’. A huge number of engines are over compressed in relation to the octane of the fuel that is available. The amount of compression to be used needs to be sorted out before the engine is rebuilt. We all tend to want to use as high a compression ratio as possible and with good reason, but you do need to be mindful of the limitations.

As a guide, 9.25:1 compression ratio is the maximum possible for use with 91-93 RON octane fuel, 9.75:1 is the maximum possible for use with 95 RON octane fuel and 10.5:1 is the maximum possible with 98 + RON octane fuel (a super unleaded fuel such as Shell Optimax in the UK). Racing engines will usually stand 12.5:1 compression ratio using 98 + RON octane super unleaded fuel with or without an additive such as TetraBOOST, but this is the limit.

STANDARD SPARKPLUG LEADS (wires)

The standard Lucas suppression sparkplug leads are of excellent quality and can be used with confidence, knowing that they will perform as required. Leads on any racing engine should only be used for 1 year.

As a general rule the lower the resistance in the sparkplug leads the better, and 5-10kOhms of resistance is generally acceptable.

J.E. Developments racing engines frequently use standard suppression ignition leads and rev to 7000rpm without problems.

Massive loss of potential power can occur if every aspect of the ignition system is not operating at peak efficiency.

Sparkplug lead location

There was a change made by the factory to the position of the sparkplug leads on the distributor cap from 1987 onwards. At this point they all moved around the cap by one position to reduce the possibility of ‘cross firing’ between cylinders 5 and 7.

CONDENSER

It used to be common practice to replace the condenser whenever the points were replaced, when in fact the old condenser was frequently better than it’s replacement! When the points are replaced, always check to see if the deterioration of the two contact faces looks to be much the same. If it does, don’t replace the condenser. If on the other hand one contact looks to be much worse for wear than the other, to the extent that one point looks to have a rough looking hollow in it while the other has a rough looking raised section on it, replace the condenser as it isn’t working as it should. Don’t replace a condenser unless it needs to be replaced.

Further reading

For those seeking in depth information on optimising and modifying ignition systems How to Build & Power Tune Distributor Type Ignition Systems by Des Hammill is recommended reading. One of the SpeedPro series, the book covers, in detail, the methods of marking crankshaft pulleys and altering distributors for improved performance and much else on the important subject of ignition systems.
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Thunderbolt
Messages : 1810
Inscription : 07 janv. 2014 10:57
Voiture(s) : Chimaera 400 / Jaguar XJ6 S3
Localisation : Alsace

Re: Réglage avance à l'allumage

Message par Thunderbolt »

Si je comprends bien, il faudrait régler l'avance à 34° à 4500 tr/mn (28° pour les moteurs de 4.5l ou plus) pour une Chimaera 400 pour 10 à 12° au ralenti (14 à 16° pour les moteurs de 4.5l et plus):
"The springs allow the advance to start at about 1000rpm and full advance will be achieved at about 4500rpm".

Je suppose alors que ces 34° doivent correspondre à 28/30° à 4000 tr/mn comme l'indique S. Hayes (34°à 4000 tr/mn cela me paraît bien élevé...), non??

J'ai en tout cas réglé l'avance à ce niveau-là il y a quelques jours ( cela donnait 11° au ralenti), et il m'a semblé que le moteur était désormais effectivement un peu plus réactif, avec une meilleure facilité à poursuivre sa progression au-delà de 4000 tr/mn.
lolo106
Messages : 732
Inscription : 28 oct. 2008 14:10
Voiture(s) : MORGAN PLUS 8 3.9 1991

Re: Réglage avance à l'allumage

Message par lolo106 »

En gros c'est ça.
Perso sur ma MG : V8 rover 3.5l, bas taux de compression j'ai 10° au ralenti (capsule à dépression débranchée) et 36 à 4000 tr/min.
Après, plus le taux de compression est élevé moins il faut d'avance (dans les tours) mais toujours 10° à 1000 tr/min.

Un point à vérifier sur nos moteurs (V8 Rover) c'est l'indication du PMH sur le volant moteur car il arrive qu'il y ai un décalage et donc une erreur de réglage possible. Pour vérifier il faut utiliser le puits de bougie du cylindre 1 et un comparateur avec une rallonge. On cherche le PMH en s'arrêtant environ 10° avant (on fait une marque) et 10° après (on fait une marque) et le PMH ce trouve au milieu de ces 2 valeurs. Pour bien faire, faire plusieurs fois la mesure et dans les 2 sens (question de rattrapage de jeux).

Un problème sur les V8 rover moderne c'est l'allumeur qui a des problèmes de fiabilité, des solutions existent pour s'affranchir des du système de masselottes et de plateau qui bouge en fonction de la dépression de la capsule :

http://www.aldonauto.co.uk/aldon-amethyst
http://www.simonbbc.com/ignition-contro ... e-ignition
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