If not, adjust the timing until it does so. If the timing is right, the appropriate mark should appear stationary in line with the fixed pointer. If you are timing from a static figure only, temporarily adjust the carburettor idle-stop screw (See Adjusting an SU carburettor) to give the slowest idle speed at which the engine will run steadily. Start the engine and get it to run steadily at the correct speed for the test. If necessary, disconnect the vacuum-advance tube. With the more expensive induction-trigger type, it does not matter whether the engine is running or not. Some strobes have an inductive trigger that clips round the plug lead. The vacuum advance Vacuum advance check Vacuum advance Distributeur Vacuum advance check Find the mark or marks that you need, and dot them with white paint or chalk so that they stand out.
Work in a shaded place so that the light shows the marks clearly. If you cannot get a stroboscopic timing figure, use the static figure and set the timing with the vacuum advance disconnected and the engine idling as slowly as possible. This set of measurements is always made with the vacuum advance disconnected, so it shows whether the centrifugal-advance mechanism is working properly. You may be able to find out the whole 'advance curve' for different speeds.
If it is stated for a high engine speed there may be a tolerance of a few degrees, for example 31-33/3,000. The figure may be the same as the static figure. 1).įind also whether to measure with the vacuum-advance mechanism disconnected or not - the centrifugal-advance system is never disconnected.Ī typical timing figure is 13/1,000, meaning 13 degrees before top dead centre ( BTDC) at 1,000 rpm. Alternatively, use a separate unit - which can be read from under the bonnet.įind out from a car handbook or a dealer the maker's stroboscopic timing figure, and which cylinder to use for the check (almost always No. If your car has a tachometer - or rev counter - use this to measure the engine speed. The timing must be set at an exact engine speed. Most strobes have a metal spacer connection which fits between the sparkplug and the plug cap, but more expensive models have an 'inductive trigger' that clips around the plug lead and can be fitted and removed while the engine is running. If you advance or retard the ignition, the mark appears to move a short way and then stop in a new position.īuy or hire a xenon strobe if possible, for it is brighter than the cheaper neon type. The strobe light is a xenon or neon flash tube, which flashes very briefly at the moment of firing, so that the timing mark is lit only when it is opposite the fixed pointer.Īs this happens again and again, the effect is to make the mark appear stationary. A stroboscope is simply a light connected to the sparkplug of the cylinder that is used for timing.Įvery time the plug fires, a timing mark on the crankshaft pulley is just passing a fixed pointer on the engine.
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