This guide captures ‘bygone’ advice on how to check and adjust ignition timing on a Classic Car. It is part of a series I am building that describes what to do on a Classic Car Basic Service.
Contents
- How to check ignition timing
- Where to find Ignition Timing marks
- What is TDC or Top Dead Centre
- What to do if your car has no TDC Top Dead Centre timing marks
- How to set Ignition Timing
- How to adjust timing using the Static Ignition Timing method
- How to adjust timing using Strobe Light method
- Monolithic Ignition Timing
- Electronic Ignition Timing
- Road Testing Ignition Timing
- What is Pinking and how to solve it on a Classic Car
- About this site
Useful information for Classic Car and Retro Car enthusiasts, as many of these tasks are no longer required on modern day cars.
Remember folks these are ‘bygone guides’ … useful but the safety and personal protective equipment measures are reflective of bygone awareness. Stay safe.
How to check ignition timing
Before we crack on you may want to gain an overall understanding of Ignition Timing Basics here.
Before starting work on ignition timing, you need to know three things :
- Which of your cylinders is No. 1.
- Which cylinder is used for the timing procedure. (In nearly all cases it is No. 1, but there are rare exceptions where the rear most cylinder (No. 4, No. 6 or No. 8) is used instead.)
- At what point (that is… how many degrees of crankshaft rotation before TDC-the timing cylinder should fire) (This varies from car to car and also varies for the same car between countries which have strict emission-control regulations and those which do not.)
So gather your facts from appropriate country specific workshop manuals. Do not just google it using car marque and model as you may receive the wrong information.
The actual job involves four stages:
- Establishing, on a fixed part of the engine, a mark corresponding to TDC.
- Establishing on a rotating part of the engine, such as the fan pulley or the flywheel, a mark to represent TDC.
- Also establishing on the rotating component another mark ‘the advance mark’ representing the number of degrees before TDC that combustion should take place.
- Adjusting the distributor so that No. 1 (or other appropriate) cylinder fires exactly as the advance mark on the fan pulley or flywheel lines up with the fixed mark, corresponding to TDC, which you have made on the engine.
Where to find Ignition Timing marks
The first step in timing the ignition is to find the timing marks or, if the manufacturer has failed to provide any, to make some. Pictures below show the most likely places for the marks to be.
If the timing marks are on the flywheel, they can usually be seen by removing a small plate bolted to the bell housing at the back of the engine. This plate is generally at the top or side, but on a few cars it is at the bottom.
On some cars with transverse engines, the marks can be seen only with a small hand-mirror and a torch. Stick the mirror to the flywheel housing with a piece of chewing gum and a suitable support while you work.
Alternatively, the timing marks may be on the fan pulley or on cars with crankshaft vibration dampers behind the fan pulley on the dampers.
What is TDC or Top Dead Centre
The next step is to determine what the marks identify.
On the fan pulley or wherever, you may find only a single mark. If it is inscribed ‘Top’ ‘TDC’ “No. 1′ or ‘O °’ then it is certainly the TDC mark – the one that denotes that the cylinder used for timing purposes is in the ‘fire’ position.
If it carries no identifying symbols, it is still almost certainly the TDC mark, except on late Volkswagens where, just to confuse the issue, it is the advance mark.
If you find two lines about 2.5 cm or l inch apart, the one that comes up first as you rotate the engine is the advance mark, the other the TDC mark.
Some engines have two advance marks set close together. These are for use when the engine is run on different grades of fuel. The higher the octane rating ( or star rating) of the fuel, the more advanced the timing will be. Useful to know in modern times.
On the pulley or damper, some manufacturers provide an elaborate scale, showing as many as 24 ° before top dead centre (BTDC) and 16 ° after top dead centre (ATDC) as well as the actual TDC mark.
Others provide only one groove on the crankshaft fitting, but a calibrated scale bolted to a rationary part of the engine. In both cases the scale allows the timing to be varied according to the conditions under which the car may be run, altitudes higher than sea level for example, or hot or cold climates.
Whatever marks are provided, it is a good plan to fill them carefully with white paint to make reference easier.
What to do if your car has no TDC Top Dead Centre timing marks
Should no timing marks exist, the correct positions will have to be calculated and marked.
For the TDC mark, the procedure is to get the piston in the timing cylinder (usually No. 1) exactly to the top of its compression stroke. Then you make a narrow groove in the rim of the fan pulley or damper and make a corresponding mark precisely in line with it on an adjacent, stationary part of the engine.
To do this the engine must be turned in its correct direction of rotation. This is most easily done with the spark-plugs removed, but first mark each plug lead by number to avoid confusion later.
There are several ways of turning an engine slowly. One is to use the crank handle, in the unlikely but happy event that your car has one.
Another is to turn the engine by pulling on the fan belt, although this is difficult with big engines of 3 litres or more and engines with electric or viscous coupling fans should not be turned in this way.
Yet another method is to use a suitable socket and a long drive bar on the nut securing the pulley or damper to the crankshaft. A final alternative although not on cars with automatic transmission is to put the car into top gear, turn the steering on to full lock, and push the car by one of the protruding tyres.
Never turn the engine over backwards; you will get a false reading.
Since making the TDC mark requires that No. 1 cylinder be on the compression stroke (when both inlet and exhaust valves are shut at the same time), the rocker cover must be removed so you can see when this takes place.
On overhead camshaft engines, the camshaft cover must be removed. No. 1 piston is on its compression stroke when the springs of the relevant valves are not compressed but are their normal length. You can see whether they are simply by looking at adjacent springs, some of which will be in noticeable states of compression.
To get an exact reading of TDC it is necessary to smear the threads of No. 1 cylinder’s spark-plug hole with a good bubble-blowing liquid, such as detergent or a strong soap solution. To keep the bubble a manageable size, screw in the spark-plug about half to one turn or, alternatively, use a tapered wood plug with a groove cut down one side.
As you rotate the engine, the bubble will increase all the time that the piston is rising on the compression stroke. Once it has passed TDC, the bubble will shrink or burst.
Repeat the bubble making procedure a few times to get the feel of where TDC is. You will need to turn the engine so that other pistons reach TDC before No. 1 will return to that position.
Once you are sure that you have the bubble at its maximum height, make your initial marks as described above.
Marking the Timing Mark
Next, you want a timing mark the right number of degrees ( as explained earlier) in advance of the TDC.
There are two ways of doing this. One is to measure the diameter of the fan pulley with a ruler and cut a circle of card exactly the same size as the pulley. Then you measure out the required angle with a protractor and transfer the timing mark to the pulley.
For the other method, start by measuring the pulley diameter.
Multiply this by 22. Then multiply by the number of degrees of ignition advance required. Divide the result by 7 x 360 (2520). This will give the required distance around the pulley rim. The formula is:
Finally, use a flexible steel tape to measure the distance around the pulley rim.
Whichever method you use, remember that as the engine rotates the timing mark must come up ahead of the TDC mark. As you face the engine from the fan end, for example the direction of rotation will be clockwise so the new mark will be to the right of TDC. The new mark is BTDC, before top dead centre.
How to set Ignition Timing
There are three methods of setting the ignition timing:
- The static method, carried out with the engine stopped. This method can be used on any car, but it is not precise, and final adjustments must be done later under road-test conditions.
- The stroboscopic light method, carried out with the engine running at a pre-determined number of revs. It is more precise than static timing, but works only on cars with a tachometer (rev counter).
- Monolithic timing. This relatively new method works only on later classic cars whose crankshafts are made specially to suit it.
Adjusting the Points
Before you begin checking the ignition timing, the contact breaker points must be adjusted.
How to adjust timing using the Static Ignition Timing method
The static method of ignition timing uses a 12-volt bulb in the middle of a length of electrical flex;
This is connected across the contact-breaker points in the distributor. or coil. With the ignition on, the engine is turned over by hand so that the bulb lights up at the instant at which the relevant spark plug would normally produce a spark.
By this means it is possible to keep adjusting the distributor until the light starts coming on when the BTDC mark on the flywheel (or wherever) is precisely aligned with the fixed reference mark.
If the light comes on before the piston is at BTDC, the ignition is advanced and must be retarded; if it comes on after BTDC, the ignition is retarded and must be advanced.
Ready made 12-volt bulb kits can ( or could be) bought from most motor accessory stores. Alternatively you can make up your own by soldering a length of electrical flex to each terminal on a 12-volt bulb and then soldering a crocodile clip to the other end of each wire.
The procedure for static timing is in the pictures shown below but two extra aspects must be borne in mind.
If the timing marks are on the flywheel, or if the engine is to be turned by rocking the car in gear, you will probably need an assistant.
When you come to make the final adjustments to the timing by means of the vernier scale (fine adjuster) on the distributor, a maximum of six clicks in either direction is all that is allowed, even though most distributors will move 11. Any more than six and you should revert to rotating the distributor body.
How to adjust timing using Strobe Light method
A stroboscopic timing light uses a neon, or similar, high voltage bulb that triggers a flash of very short duration virtually instantly it is triggered. This flash is triggered by current in the high-tension lead to No. 1 spark-plug. So each time No. 1 sparks, the bulb lights up.
To use a strobe light, you shine it on the timing marks (on the crankshaft pulley or damper, or on the flywheel) while the engine is running. Since the strobe flashes only when No. 1 fires, it makes the pulley (or whatever) appear stationary.
Hence it is easy to see whether the advance mark on the pulley is exactly in line with the fixed mark on the engine.
But there is one small problem. The number of degrees BTDC that No. 1 fires is not a constant; it varies with the speed of the engine. (Two mechanisms, the centrifugal advance and vacuum advance, control this variation.) So to use a strobe you need to know the correct dynamic ignition timing at a given speed.
For example, 7 ° BTDC at l000rpm-and to run the engine at the correct number of rpm. For this reason the car must have a rev counter. (How to fit a REV Counter)
Here are the most watched Timing Lights on eBay. Don’t be tempted to spend a fortune a Power Spark or Accuspark will be ideal for a simple classic car.
Workshop manuals will tell you the correct advance angle and corresponding rpm for dynamic timing, and this angle should be marked on the fan pulley in the same way as if for static timing.
The procedure for timing by strobe light is shown below. But before you begin, it is important to disconnect the vacuum advance pipe (arrowed in picture below).
Safety Precautions & Top Tips
Some strobe lights have leads which connect to the battery as well as to No. 1 spark-plug. When using these, always connect first to the battery, then to No. 1 plug.
When disconnecting always remove first the No. 1 plug lead then the battery leads. This way you will avoid getting a high voltage shock if you touch the battery connections.
A strobe light makes everything that is rotating at speed appear stationary. So keep away from moving parts.
It is a wise precaution to remove the fanbelt during the period of adjustment, since the fan would be virtually invisible. Do not forget to replace it when the operation has been completed.
A further precaution, although not connected with safety, is to make sure that the BTDC mark on the pulley, damper or flywheel is clearer than all the others (for example, the TDC mark). This will prevent your setting the timing to the wrong mark.
If your car has timing marks on the flywheel (unless it has a transverse engine) you will need the help of an assistant.
Monolithic Ignition Timing
Monolithic timing was a later development pioneered in the US by Ford. It uses a machined indicator incorporated into the crankshaft during manufacture.
As the crankshaft revolves the indicator sends an electromagnetic impulse to the monolithic timing equipment installed on the engine. This impulse triggers a timing light and adjustment is carried out in the same manner as with a strobe light-by turning the distributor until the timing marks are aligned.
This method is claimed to be more accurate than using marks on the fan pulley or damper since it is based on the crankshaft itself, not on a component separated from the crankshaft by a rubber ring which might distort at speed.
Electronic Ignition Timing
I will be providing a more detailed explanation of Electronic Ignition timing and conversion in a later post. However here are the basics.
There are two main kinds of electronic ignition
The simpler cheaper sort which makes use of the existing contact breaker in the ignition system and the dearer more sophisticated sort known as ‘contactless’.
Where the existing contact-breaker is retained it is possible to time the ignition statically but most manufacturers recommend stroboscopic timing.
With electronic ignition it is possible to set the ignition right up to the limit of the car manufacturer’s recommended advance because of the accuracy this type of ignition can maintain over the whole range of engine speeds. To gain the maximum benefit from it, therefore, really precise timing is needed.
Contactless ignition systems can also generally be timed only by strobe light. However some systems, such as the Kenlowe Kenlomatic, incorporate their own timing light. This works in the same way as the 12-volt bulb in conventional static timing.
Road Testing Ignition Timing
Road testing is the final stage in setting the ignition timing.
Before you begin, ensure that all spark-plug leads have been replaced in their correct order and if you remove it the fan has been replaced.
First warm up the engine to its normal working temperature.
Then accelerate in top gear and at full throttle, from about 40 km/h to 65 km/h (25mph to 40mph) while you listen for any sound of pinking (a light, metallic, knocking sound.
What is Pinking and how to solve it on a Classic Car
If pinking occurs to any appreciable degree the engine is too far advanced.
It should be retarded by turning the vernier scale adjuster knob in the appropriate direction until only the barest trace is audible.
An even better test, for which you will need an assistant, is to time the acceleration in top gear at full throttle between two fixed landmarks.
Advance the ignition very slightly that is, by one or two clicks-and test again. When the time taken to accelerate between the two points is shortest, and with only a faint hint of pinking the timing of your car will be at its optimum.
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