what is "BLOW BY"???? and how does it work/happen?

[MUSS]

just interested to know how it happens and works?

[Ruggers]

its were the psiton rings are worn and allowing gases past and into the crankcase causing postive pressure in the crankcase. can be checked by pressurisng the cylinder and seeing if it holds pressure and listening though the oil filler for air leaks. worn valves also may let air past them

[chimpboy]

Your engine works when fuel + air are burned inside the ccombustion chamber, causing rapid exansion and therefore pushing the piston down. The piston then turns the crank which drives the gearbox and ence the wheels.

The expansion of gas that forces the piston down relies on the combustion chamber (formed by the head, the cylinder, and the piston) to be sealed.

Sometimes, in a worn engine, the rings around the piston don't seal properly against the cylinder wall.

When this happens the expanding gases can escape past the piston into the crank case. This is blow-by. It means less power for obvious reasons.

Jason

[pegasus]

You also have a breather hose on top of your rocker cover. This is the breather for your crankcase (some engines are differnet, or have this in different places) this hose eventually goes into your air intake, for pollution control etc..

The pressurised gas from your crankcase (caused by blowby) will vent through this hose. The gas will be oily. This then feeds into your air intake to be burnt. This means some oil is then being burnt, causing the car to generate blue smoke. There has to be a fair bit of blowby for this to occur..

Stew