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What is Engine 'Pinking' ?


perksy

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Pinking is a term used to describe a noise made by the engine under load when one or two parameters are not in an ideal range.

It can occur when iffy fuel is used or when the compression is too high, carbon build up on the piston crown (which raises compression) but most commonly it occurs when there is too much ingition advance. It is *very bad* for the longevity of the engine.

It is quite easy to induce pinking on a car that uses a distributor using bob weights to advance the ignition. If you snap the throttle open, the distributor reacts a little too slowly for the sudden increase in fueling. The excess fuel detonates too early and you hear the distinctive pinking noise. If it happens during more normal throttle application or simply when cruising around you have a serious problem and you should not drive your car until the fault is rectified. Pinking really will destroy your engine! You can hole a piston or damage valves, so pinking should be attended to.

On a car with mapped ignition or fuel injection you should never have this situation. If you do, again you need to rectify it but you do so by modifying the ignition map.

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Nearly... :p  ;)

A little bit of confusion reigns with the terminology. Pinking is a light metallic rattling sound created by the piston rattling within the cylinder bore as it goes past TDC and onto the power stroke - and is normally caused by a tad too much advance. If the engine isnt working hard when it happens, it is unlikely to be an engine killer. But it is a good indiction that you are pushing your luck :t-up: Quite often it is possible to hear modern cars 'pink' under certain conditons...

Pre-igniton (or sometimes known as detonation) *is* an engine killer - and an efficient one too. This is caused by the mixture exploding uncontrollably, before the spark plug has had it's time to ignite the mixture. Any number of things (or combinations of) can cause it - weak mixtures, excessive compression ratio, carbon build up, incorrect spark plug heat range, igniton timing that is way too far advanced, etc, etc.

Interestingly, the (fairly common) example set by Blatters may not be either of the above, but something known as 'knock'. This tends to occur at lower engine speeds, and is caused by the collision of two flame fronts within the cylinder - one created by the spark plug, and the other by the gases around the edge of the cylinder. These 'outer' gases tend to have a weaker mixture concentration, and will ignite on their own under certain conditons.

Indeed, snapping the throttle open on a car with a mechanical distributor, will get a dose of 'rich' mixture, but that actually helps curb pinking/pre-igniton. As stated, the bob weights will only be seeing the engine rpm, so advance hasnt increased. If the vacuum advance mechansim is connected, advance will actually decrease. Again, many things influence knock, such as compression ratio, mixture mix/swirl, fuel quality, igniton timing, engine design/cylinder layout etc, etc.  

So in summary - pinking isn't necessarily an engine killer, but consider it to be a warning sign to things looked at. Knock not a pleasant sound at all (a heavier sound than pinking), and is a sign things are definately not as they should be. Pre-igniton will waste your engine. A truly awful sound - but sometimes impossible to detect if the engine is flat out. The first thing you will know about it is bad misfire created by the valves and/or pistons that have melted away...  :(

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