crankcase vent question

paracer · Post by **paracer** » Mon Mar 27, 2017 3:07 am

So, I'm wondering if I am missing something simple here.

I currently have two atmospheric vents on my engine's crankcase. One is where the dipstick goes. The other is on the valve cover.

My question is why I experience such a difference in the air pressure at each vent. With a finger over the dipstick vent I can barely feel any pressure at all, if any.

However, the vent on the valve cover is very different. I feel a distinct, pulsing, positive pressure.

It seems weird to me that these vents don't have the same condition. I have never completely torn apart a gy6 engine, so I don't know if maybe there is a separation between these two parts of the engine that I'm not thinking about. Does anyone have any insights?

babblefish · Post by **babblefish** » Mon Mar 27, 2017 5:22 am

The part of the crankcase that your dipstick is in is separated from any crankcase pulses by the crankcase oil. In other words, it is not at atmospheric pressure, but it is under some pressure from the oil pump. Try removing the dipstick with the engine running and you'll see what I mean. Warning: have some paper towels handy...

scootERIK · Post by **scootERIK** » Mon Mar 27, 2017 5:12 pm

babblefish wrote:The part of the crankcase that your dipstick is in is separated from any crankcase pulses by the crankcase oil. In other words, it is not at atmospheric pressure, but it is under some pressure from the oil pump. Try removing the dipstick with the engine running and you'll see what I mean. Warning: have some paper towels handy...

I forgot to put the dipstick back in after adding some oil and started my Buddy, oil ended up 5-6 feet up the garage door that was 4' from the scooter. It was a mess but I learned a lesson to always keep track of the dipstick when checking and adding oil.

babblefish · Post by **babblefish** » Mon Mar 27, 2017 7:40 pm

scootERIK wrote:
babblefish wrote:The part of the crankcase that your dipstick is in is separated from any crankcase pulses by the crankcase oil. In other words, it is not at atmospheric pressure, but it is under some pressure from the oil pump. Try removing the dipstick with the engine running and you'll see what I mean. Warning: have some paper towels handy...
I forgot to put the dipstick back in after adding some oil and started my Buddy, oil ended up 5-6 feet up the garage door that was 4' from the scooter. It was a mess but I learned a lesson to always keep track of the dipstick when checking and adding oil.

, sorry, I couldn'd help it...

paracer · Post by **paracer** » Wed Mar 29, 2017 1:07 am

I too have a similar story. I drilled a small hole through the dipstick in an attempt to vent excess crankcase pressure. That little hole was like a nozzle.

Okay, so I can understand now that I should not be worried about the difference in pressure between the two vents. Now, my other question would be, do I need two vents? If I have a atmospheric vent on the valve cover, do I need one on the dipstick?

Thanks for the replies!

babblefish · Post by **babblefish** » Wed Mar 29, 2017 8:18 am

paracer wrote:I too have a similar story. I drilled a small hole through the dipstick in an attempt to vent excess crankcase pressure. That little hole was like a nozzle.

Okay, so I can understand now that I should not be worried about the difference in pressure between the two vents. Now, my other question would be, do I need two vents? If I have a atmospheric vent on the valve cover, do I need one on the dipstick?

Thanks for the replies!

Why do you feel you need to vent the oil galley to atmosphere? The oil pressure to push the oil through the wire mesh filter will be lost, so probably not a good idea.

paracer · Post by **paracer** » Wed Mar 29, 2017 11:31 am

because when I did that I did not know that the pressure in the crankcase assists with pushing oil through the strainer.

I should probably find a dipstick at this time.

babblefish · Post by **babblefish** » Wed Mar 29, 2017 1:07 pm

paracer wrote:because when I did that I did not know that the pressure in the crankcase assists with pushing oil through the strainer. I should probably find a dipstick at this time.

The oil pump pushes the oil through the strainer (and out the dipstick hole), not the pressure in the crankcase.

paracer · Post by **paracer** » Thu Mar 30, 2017 12:02 am

babblefish wrote:
paracer wrote:because when I did that I did not know that the pressure in the crankcase assists with pushing oil through the strainer. I should probably find a dipstick at this time.
The oil pump pushes the oil through the strainer (and out the dipstick hole), not the pressure in the crankcase.

Ok. So it is good to vent both the valve cover and the crankcase. Relieving the pressure through a dipstick vent would aid the system by reducing the resistance that the oil pump is pushing against.

That is what I get for trying to convey my thoughts before I have had my coffee.

Thanks!

Syd · Post by **Syd** » Thu Mar 30, 2017 3:32 am

If it was truly food to vent the case, don't you think PGO would have designed one in?

babblefish · Post by **babblefish** » Thu Mar 30, 2017 7:33 am

Venting the valve cover vents the crankcase because they are directly connected through the head and cylinder. From the factory, the crankcase gases are vented through a PCV and into the carb intake.