Originally Posted by jkubica

Hi
The idea is not to allow any pressure to build up in the crankcase - that's the purpose of having the breather hose on the valve cover going to the air filter/intake. The pressure is from blowby - combution gases that are leaking past the piston rings and pressurizing the crankcase. If not vented by the breather hose, the blowby will build up enough pressure to force oil out the dip stick and even blow out the oil seals.

You don't say what engine you have, but many 617s have an oil serarator in the air filter that removes the excessive oil from the blowby and returns it to the crankcase. The de-oiled blowby is then directed to the intake where it is burned in the engine. If the oil separator is badly gunked up - it can reduce the blowby venting resulting in higher crankcase pressure.

Oil dipstick level can't be measured with the engine running because of all of the oil being spashed around by the crankshaft anf blowby gases. To measure the dipstick oil level the engine must be off and allowed to sit a few minutes to allow all the oil in the upper engine time to drain back into the crankcase.

You can check for blowby by letting the oil fill cap sit loose on the valve cover hole while the engine is ar idle. Its OK for the cap to dance around a little but it shouldn't blow off.

Good Luck,

Joseph