An ignition system in good condition and properly set-up is critical to rapid starting, eager performance and optimum fuel-efficiency. Kim Henson advises on how to get the best from your classic’s set-up

Winter months highlight deficiencies in a classic’s ignition components and any incorrect settings will only make the problem worse. If you’re not planning to use your vehicle until the spring, such ailments may result in serious difficulties when trying to get the car running again. If you use your classic in the cold and damp months, it’s even more important to have the ignition system in top condition to ensure positive starting as well as efficient, economical running.

It’s wise to carry out regular checks on the system; your car’s handbook or workshop manual should provide the recommended frequency and required settings. In the absence of specific recommendations, the ‘rule of thumb’ for a car with a conventional ‘coil and contact breaker’ ignition is that points should be inspected, cleaned and re-set every 3000 miles (or annually, whichever comes first), and renewed regardless every 6000 miles. Inspect associated components at the same time and renew if necessary.

Spark plugs should be scrutinised, cleaned and re-gapped as required every 6000 miles (or once a year), and renewed every 12,000 miles. Exceptions to this general advice include electronic breakerless systems, and ‘long-life’ spark plugs.

At the outset, always ensure that the engine is in sound mechanical condition with good compression readings and that the valve clearances are correctly set. In addition, don’t make any adjustments to carburetor or fuel injection settings until all the ignition system checks have been carried out.

SPARKS

Ideally a soft, brass-bristled wire brush should be used for cleaning soot and other debris from spark plug electrodes. Soft, non-damaging bristles can reach deeply into the plug’s aperture to oust all deposits. After cleaning, re-gap the plugs if required by gently bending the ‘side’ electrode to the required position. Assess the gap dimensions using feeler gauges and adjust to the car maker’s recommendations.

When re-fitting spark plugs, sparingly apply copper-based anti-seize compound to the threads; this is particularly important if the engine has an aluminium cylinder head. If the plugs are taper seat types, it’s ESSENTIAL that these are not over-tightened or removal can be near-impossible!

For some cars, copper-cored versions of the original spark plugs can be used with advantage; check suitability/availability with the spark plug supplier. Both the high and low tension wiring circuits needs to be up to the job. Ensure that all cables are clean, in good condition and securely connected at each end.

Ageing high tension cables can cause problems, especially if they are ‘carbon string’ suppressed types. These can break down and cause misfires after just 18 months or so. More costly but far superior are copper-cored types used in conjunction with high quality spark plug connector/suppressor caps.

Copper-cored cable can still be purchased ‘off the roll’ from many motor accessory shops and classic automotive electrical specialists. Your existing cables can be used as a guide to establish the length required.

DISTRIBUTION

Inspect the distributor cap and rotor arm, looking closely for cracks in the bakelite/plastic body of each unit, and for signs of electrical ‘tracking’, plus erosion of the metal contacts.

It’s essential that the carbon bush − usually spring-loaded − in the centre of the distributor cap is in good condition and securely attached. If in doubt, fit a new cap and rotor arm.

Wear can accumulate in the bush/bearing within the body of the distributor. This results in excessive side play in the main distributor shaft, making it virtually impossible to correctly set the points gap/dwell angle. Check for this, and if necessary install a replacement distributor of the same type or have a new bush made for your own unit.

Contact points MUST be clean and correctly set. Use feeler gauges to initially set the gap and ideally confirm the setting by checking the dwell angle reading using an automotive electrical test meter. The dwell angle reading provides a more accurate indication of the correctness of the gap. This relates to the number of rotational degrees of the distributor shaft during which the contact points are closed to re-energise the primary windings of the coil. Ensure that all the fragile low tension wiring within the distributor assembly is intact and firmly connected.

Follow your car maker’s advice with regard to lubrication of the distributor. Typically a few drops of engine oil are applied to the centre shaft through apertures in the baseplate. VERY sparingly smear high melting point grease onto the distributor cam to lubricate it. Don’t overdo lubrication or the contact points will become contaminated and misfires will occur.

After fitting contact points, ALWAYS re-check the ignition timing in accordance with your car’s handbook/workshop manual. Note that dynamic timing checks carried out using a strobe lamp at different engine speeds are more accurate than static assessment. If necessary you can paint your own timing marks on the crankshaft pulley/engine by reference to the ‘top dead centre’ position of No.1 cylinder’s piston.

USEFUL INFORMATION

Always use high quality ignition components; inferior types may let you down.

Moisture can play havoc with ignition systems and often a quick application of water dispellant spray (to the ignition coil, high tension leads, spark plug connectors and distributor cap) can make the difference between the engine starting – or not…

Some classics incorporate a ‘ballast resistor’ within the ignition system; this requires the use of a special ignition coil (with a lower voltage rating than the standard 12 volt type). Starting/running problems will arise if the unit fails or the wrong type is fitted.

HOW EASY

** (Two spanners)

Ignition checks are reasonably straightforward but you will need to work methodically and consult the car’s manual for settings etc. Don’t touch uninsulated plug leads when the engine is running as you will get a shock. Keep all loose clothing, leads and tools clear of belts and pulleys.

1. For working on the ignition systems of virtually all classic cars you will need a set of feeler gauges for setting/checking gaps on spark plugs and contact breaker points, plus ideally a set of ‘ignition’ spanners for tackling the tiny nuts/bolts employed.	2. Spark plugs are fundamental to any engine’s performance. Every 6000 miles, remove the plugs, check their condition, clean and re-gap them. Renew plugs regardless every 12,000 miles or earlier if the electrodes are visibly worn.	3. High tension leads must be clean and dry, or electrical ‘tracking’ to earth can occur. Regularly apply a water dispellant spray, and carefully wipe the leads with a clean rag. Beware of ‘carbon string’ suppressor leads (see text).
4. Unclip or unscrew the distributor cap, wipe clean inside and out and closely examine the metal segments within (usually brass or aluminium). Also check the central carbon brush. Serious erosion will result in misfires; fit a new cap if contacts are worn.	5. Inspect the rotor arm and condenser, also check for excessive side play in the main distributor shaft, and assess the condition of the baseplate assembly plus the vacuum advance capsule (where fitted). Deficiencies in these components spell problems.	6. Examine and re-set the contact breaker points every 3000 miles and renew every 6000 miles as the surfaces of the points become pitted and ‘burnt’. Using feeler gauges, initially set up the points gap according to the manufacturer’s specification…
7. …and then, if available, use a dwell meter to confirm whether the dwell angle is within the specified tolerance. An automotive multi-meter like this is a good investment and helps assess voltage, dwell angle, circuit continuity and engine speed.	8. If you find it difficult to obtain correct points gap/dwell angle readings, ensure that the contact points are opening fully as the ‘heel’ of the points set can wear. Also check the points are properly attached to the baseplate and that electrical connections are secure.	9. Ignition coils can run for many decades without giving trouble but many modern coils fail very early. Check that the unit is in good structural condition and firmly attached. On some cars a spare coil can easily be mounted alongside the original.
10. At each service, inspect the coil connections; they can work loose. Ensure that the securing nuts are tight or push-on connectors are fully attached and that cable ends are undamaged. Many coils incorporated rivets to hold the connectors; check closely!	11. Always re-check the ignition timing after fitting or adjusting contact breaker points; the timing alters as the gap is varied. Highlight the timing marks with white typist’s fluid; a 12 volt test lamp or a voltmeter can be used to check the ‘static’ timing.	12. A strobe lamp is used to check ‘dynamic’ timing with the engine running, enabling the mechanical and vacuum advance systems to be assessed at different engine speeds. The relevant data is usually found in the ‘ignition’ section of workshop manuals.
13. Some car makers used to employ ‘timing plugs’ in their engines, to help assess when the No.1 piston is at ‘Top Dead Centre’ (TDC) position of its cylinder for ignition and valve timing purposes. The plug is removed to assess piston position.	14. Vernier adjusters are found on many classic car distributors, enabling the ignition timing to be altered by up to a few degrees without the need for releasing the clamp bolt and rotating the distributor body.	15. It’s wise always to carry spare ignition system components in your boot, including a coil, condenser, rotor arm, contact points and distributor cap. Some recently manufactured reproduction replacements have proved unreliable.