Please Explain Engine Pressure/Vacuum

[IH Cub Cadet]

I'm trying to understand engine pressure and vacuum and how this works in a Kohler Command engine. I've got a crank case vent - which I assume allows crankcase pressure to vent out? But if I look at Kohler manuals, they say that if I check the engine pressure from the dip stick tube, I should read 4 or more inches of vacuum.

I'm confused. Is the engine crankcase pressurized or does it create a vacuum?

Reason I'm asking is I have a Kohler engine that is leaking oil at the crankcase seal. I would think that the engine crankcase breather would relieve this pressure, but it appears clear.

Any explanations would be much appreciated.

Thanks,
Bill

[CADplans]

Originally Posted by leeave96

I'm trying to understand engine pressure and vacuum and how this works in a Kohler Command engine. I've got a crank case vent - which I assume allows crankcase pressure to vent out? But if I look at Kohler manuals, they say that if I check the engine pressure from the dip stick tube, I should read 4 or more inches of vacuum.

I'm confused. Is the engine crankcase pressurized or does it create a vacuum?

Reason I'm asking is I have a Kohler engine that is leaking oil at the crankcase seal. I would think that the engine crankcase breather would relieve this pressure, but it appears clear.

Any explanations would be much appreciated.

Thanks,
Bill

Sounds like the crankcase vent regulates incoming air to maintain a specific vacuum!!?? -

If there were crankcase pressurized, the engine would leak more oil. Not good.

If the Crankcase were unregulated, the vacuum could get too high.

[green 4 acres]

If you are talking about a single cly Command engine they are talking about a way to check condition of the rings/cly /valves . when the piston goes up at 20-50 times a second, a vacuum will be created in the crank area a small , and short lived one , when the piston comes down it will build pressure the same way Are you sure they are not talking about closing the vent or checking at the vent and checking while cranking only? anyway I think it would take a special fitting to fit the vac gauge A cold compression wet / dry test is probably a better way to test ( if not comp release equip)or a cly leak test which takes some expertise

[IH Cub Cadet]

This engine is a Kohler CH18 twin cylinder.

Thanks,
Bill

[Oak]

I'll give it a shot. The vent is a reed type valve that is a check valve. It will let air out but not in. When the pistons are traveling up and down any pressure should go out the valve. I believe this will cause a slight vacuum in the crankcase. If your vent is clogged or your rings are worn/not seated this will cause the pressure to build and push out the seals. I would check the breather first and then maybe a leak down test on the cylinders

[Vince_o]

Green Acres and Todd are both corect.

As the cylinder moves it creates high and low preasure in the crank case. The breather acts as a check valve, only leating air move one way, out of the crank case.

There are 2 differnt valves on the commands that Ive seen. Cant remember but one gives much more problems than the other. If I remember right it was on the engs with the spark advance modual, most times you see it called a SAM unit.


On another note I have a friend that has 10 vanguards in carpet cleaning trucks. He called me about one that was blowing a lot of oil and the air fitler was covered in oil. With him in Pa I cant bring it in and do a leak down test on it. But what really was the key, oil on the air filter. After many phone calls I sent him a breather and he put it on. Now it runs much better, no more oil blowing out the seal.

He dosnt know much about engs, but he was ready to put another eng on this van. after a week of running he called me to let me know how it was running, and said he couldnt belive that that little thing could cause so much trouble.