Ignition Timing
Ignition timing
In this blog we will learn about ignition timing. So friends technically, ignition timing is exact instant at which a spark is sent to spark plug. And ignition timing is expressed in degrees of crankshaft rotation relative to Top Dead Center or TDC. Initially it is set by positioning the distributor body relative to one of the contact breaker cam lobes. The engines now days are designed in such a way that if timing for first cylinder (in case of multi cylinder) is correct then it will be ok for all other cylinders. Here we can say that first cylinder is taken as reference to set ignition timing.
In most of the engines, spark is designed to occur slightly before Top Dead Center in order to consider the time taken for fuel to burn. If ignition timing is not adjusted correctly then two cases may occur, first case is when time is set before the exact ignition timing and second case is when time is set after the exact timing. Let see what can happen in both the cases.
If Ignition timing is set before the time: In this case severe problems may arise like difficult in starting, poor performance of the vehicle and rough idling.
If ignition timing is set after the time: In this case slow & jerky cranking with warm engine may occur. Detonation may also be experienced while accelerating.
How to adjust ignition timing?
A timing mark is provided on crankshaft pulley which must be opposite to specified degrees marked on some stationery part of engine. This approach is used in vehicles under make of Audi, Ford, Benz, Mazda etc. In the second approach the crankshaft degrees are marked on some flywheel while a stationery pointer is attached to the engine block. This way is used by BMW, Dodge, Honda, Renault etc.
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| Mercedes Benz |
What points should be considered before checking or setting ignition timing?
- The dwell must be correct.
- The engine is running at its normal temperature.
- The engine is running at specified timing speed.
- The vacuum hose is
disconnected from the vacuum advance unit.
What is the procedure to check ignition timing?
1. Start the engine and see that same has reached the normal operating temperature.
2. Connect the timing light to first cylinder or reference cylinder and aiming it on the crankshaft pulley or the flywheel, as the case may be check whether the stationery pointer is opposite the specific mark.
3. If not loosen the distributor locking bolt or nut and turn the distributor in the desired direction so that the stationery pointer comes opposite to the specified timing mark.
4. Lock the distributor bolt/nut and recheck the timing with the timing light. If required, readjust and check to ensure that it has been set correct.
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