mithun

The vibration that you are feeling when the engine is running. It varies depending on engine.

moeed

Great info there!

iorhld

at low rpm when the throttle is partially open,the ignition timing is retarded.the flame front from the spark plug travels slowly.as a result,there are two individual seperate combustion inside the chamber,one near the spark plug and other at the very extreme end of the cylinder.as a result of two seperate combustions,we hear two distinct sounds in a single cycle of piston operation.thus the "knocking" term is used to describe the effect.

Andante

Actually, that's not true. With retarded ignition timing the fuel air mixture still burns at the same speed as it would otherwise.

Knocking in an engine is a phenomenon that is caused by premature ignition or detonation.

Premature ignition can happen in an engine with too much of carbon deposits or because of a dirty spark plug, it's generally anything that gets too hot in the combustion chamber and ignites the fuel. Because the fuel burns while the piston is still in the compression stroke it will hammer the piston down into the connecting rod and crank. This causes the piston to rattle and you can hear it.

Detonation can happen when the fuel is of inferior quality or in high powered engines with high compression due to too low octane rating of the fuel. It happens when the fuel air mixture ignites by itself because of exceeding temperature and pressure at which the fuel will not ignite automatically. When this happens the fuel air mixture tends to burn very rapidly in what is called detonation, which flame speeds much higher than you would get with a normal combustion ignited by the spark plug. This causes a very high pressure spike in the combustion chamber. Again this can be heard.

Retarding ignition timing is done to prevent pressure from building up too fast, so the piston can reach TDC before the pressure really starts to push it back down. Advancing ignition timing is done at high RPM to make sure the fuel burns on time to give the best push down on the piston during the work stroke.

I could be off by a few bits here and there, but as far as I know this should be mostly correct.
Also see: http://en.wikipedia.org/wiki/Engine_knocking

iorhld

oops,sorry for the wrong information.it's been a long time since i studied these in college.i still have in mind some of flame front details from long time back and my head is still spinning with information of the anti lag thing in WRC cars which i had asked earlier but got clarified from wikipedia.thanx andante for giving in the correct knowledge.

cicatrix

Thank you guys for this intel!

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cicatrix

In simple words: It means the engine is an integral part of the frame.
Advantage: Weight reduction and if done correctly improvement in handling too!
Now in geeky detail: In a automobile (both the 4 wheeled type and the 2 wheel type) when the engine is acting as a stressed member, the suspension loads are fed first into the gearbox and then through the engine into the chassis. In this type of engine design the block itself has to be stiff enough to cope with these suspension loads being fed into it via the gearbox end and it into the chassis at the other, otherwise bore distortion can occur. I have also read that production blocks in cars are rarely designed to be suitable for use as a stressed member but this technology is fairly common among various sports oriented designs in cars, like few Ferraris (1995 F50 was first) and F1 cars and LeMans racers. But this type of setup is fairly common in high performance bikes (like busa) and was first featured in a sunbeam in 60's (I guess). Previously in India LML bikes used to feature this type of engines and now it has been featured again in Pulsar 135 LS.

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soumen.sam

How to keep the engine smooth and sounds like new, time by time the engine sound increase and smoothness fall. Any idea?

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Sarvajit

I guess you are talking about resonance vibrations.
Could someone please explain? I know what it is, but can't find the words to express it clearly!

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asasinationsinc

Hey
1)What does setting the timing mean w.r.t Enfields?
2)What is advance and retarding mechanisms in enfields which used the contact breaker type ignition.?
thanks.
i've googled them but the language in which they have been explained is quite technical and me being a layman is somewat difficult to understand,
thnx
regards

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