The Mechanic
Guest
Many of you fellow GS'ers have mentioned 'Pinking' and 'Knocking' as heard coming from your engines at various times.
Pinking is the laymans term for what is more correctly known as DETONATION.
Detonation is where a small pocket of unburnt fuel is cornered in an area of the combustion chamber that suddenly explodes rather than rapidly burns.
The combustion process is quite complex as this is where most money is spent when developing any cylinder head for any engine.
Air and fuel are mixed (its the oxygen that we need for power) usually above the inlet valve on carb fed engines and thence in the combustion chamber where a swirl effect takes place to help create an even mixture (air and fuel mix).On fuel injected designs this may be either direct injection or as in the case of the Boxer similar to the carb method. Just before TDC (top dead centre) say for example 12 degrees Before TDC the ignition provides an externally generated spark (2 plugs in the case of the 1150) which ignites the mixture and this burns rapidly expanding many thousands of times its own volume which gives us the force or push on top of the piston POWER STROKE.
Many people assume incorrectly that when the spark plug 'sparks' the fuel mix explodes, if this were the case then the piston crown would be destroyed before anyone had done a mile or less.
So its a rapid burn we need, but if as previously mentioned a pocket of fuel/air mix is not part of the rapid burn then the heat build up causes this pocket to explode, which in turn generates the knocking sound or pinking effect. if detonation is allowed to continue unchecked then severe engine damage will result.
Poor combustion chamber design is the main causal reason for detonation, whilst ignition timing allied with air leaks can also create the same symptoms. Worn valve stem oil seals that allow an excess of oil into the combustion chamber (drawn in down the inlet vave stem on the induction stroke) will obviuosly lower the octane rating of the fuel and thus provide the ingredients for detonation.
As the boxer engine takes a fair old while to bed in (run-in) it would not be unreasonable to expect that in heavy traffic and possibly after a fair blast that on deceleration to say traffic lights you could just draw a residue of oil into the combustion chamber and then experience knocking (detonation).
Many cars do this and some Jap bikes but the components are so much smaller that the effects usually to untrained ears go unnoticed.
Pre-ignition is a condition brought about by some particle such as carbon on the piston or in the combution chamber glowing as an ember in a fire, this causes the engine to 'run on' even though the ignition may be killed. Never switch your engine off at anything over idle speed unless it is an emergency situation as this to couls case running-on.
If your car or bike appears to be running-on its serious and needs to be stopped straight away, try stalling the engine otherwise things like timing chains, belts or worse could break!
Hope you enjoyed the read, I teach this stuff for a living and I've tried to condense the info down from a two hour lesson into a more manageable 5 mins... enjoy.
Pinking is the laymans term for what is more correctly known as DETONATION.
Detonation is where a small pocket of unburnt fuel is cornered in an area of the combustion chamber that suddenly explodes rather than rapidly burns.
The combustion process is quite complex as this is where most money is spent when developing any cylinder head for any engine.
Air and fuel are mixed (its the oxygen that we need for power) usually above the inlet valve on carb fed engines and thence in the combustion chamber where a swirl effect takes place to help create an even mixture (air and fuel mix).On fuel injected designs this may be either direct injection or as in the case of the Boxer similar to the carb method. Just before TDC (top dead centre) say for example 12 degrees Before TDC the ignition provides an externally generated spark (2 plugs in the case of the 1150) which ignites the mixture and this burns rapidly expanding many thousands of times its own volume which gives us the force or push on top of the piston POWER STROKE.
Many people assume incorrectly that when the spark plug 'sparks' the fuel mix explodes, if this were the case then the piston crown would be destroyed before anyone had done a mile or less.
So its a rapid burn we need, but if as previously mentioned a pocket of fuel/air mix is not part of the rapid burn then the heat build up causes this pocket to explode, which in turn generates the knocking sound or pinking effect. if detonation is allowed to continue unchecked then severe engine damage will result.
Poor combustion chamber design is the main causal reason for detonation, whilst ignition timing allied with air leaks can also create the same symptoms. Worn valve stem oil seals that allow an excess of oil into the combustion chamber (drawn in down the inlet vave stem on the induction stroke) will obviuosly lower the octane rating of the fuel and thus provide the ingredients for detonation.
As the boxer engine takes a fair old while to bed in (run-in) it would not be unreasonable to expect that in heavy traffic and possibly after a fair blast that on deceleration to say traffic lights you could just draw a residue of oil into the combustion chamber and then experience knocking (detonation).
Many cars do this and some Jap bikes but the components are so much smaller that the effects usually to untrained ears go unnoticed.
Pre-ignition is a condition brought about by some particle such as carbon on the piston or in the combution chamber glowing as an ember in a fire, this causes the engine to 'run on' even though the ignition may be killed. Never switch your engine off at anything over idle speed unless it is an emergency situation as this to couls case running-on.
If your car or bike appears to be running-on its serious and needs to be stopped straight away, try stalling the engine otherwise things like timing chains, belts or worse could break!
Hope you enjoyed the read, I teach this stuff for a living and I've tried to condense the info down from a two hour lesson into a more manageable 5 mins... enjoy.
