crankcase pressure

[rbig]

On a horizontally opposed twin 4 cycle, is there ever a reason why positive pressure might be a goal as to the crankcase?

Seems to me the goal is always, or nearly always, to have a slight vacuum.

 

[GregLocock]

The goal is a slight vacuum. I don't know if the main reason is HC emissions, oil leaks, or some efficiency thing. All of those would get worse with positive crankcase pressure.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[ivymike]

is it a diesel w/ a particulate filter?

 

[21121956]

Hello everybody:

In stationary Diesel engines, medium speed, four strokes, the manufacturer specify maximum positive crankcase pressure of 30 mm H2O, this is 0,002942 bar or 0,04267 PSI.

What is the interpretation (significance) of this tiny pressure? What are the consequences of a rise of this pressure?

Thanks

 

[ivymike]

You see increased probability of seal leakage, and a slight increase in oil consumption. If the pressure is higher than that, you have to wonder what has gone wrong to result in the increase in pressure. A broken ring? Ring wear? Blockage of the ccase vent system?

 

[Fabrico]

There is a significant effort afoot to "close" the crankcase on all new Diesels as early as 2007. In some areas they have already added crankcase output to emissions tests.

One thing vacuum does is reduce migration of crankcase oil past the piston rings. OEM's do it for oil control and emissions. Racers do it for several "cleanliness" reasons. The vacuum is flowing, not static, so it also clears the constantly generated oil mist from the crankcase. This is one function of a good dry sump setup.