Crankcase ventilation

[Wilfried]

That's interesting. With my oil separator, and with the standard setup, there is positive pressure when one revs the engine, less positive pressure on idle, and negative pressure on the overrun. I know this because I wanted to check that the oil separator sucks, so I removed the oil filler cap and put some cling film over the hole.

 

I don't really see how there can be other than positive pressure with the engine under load, after all one is trying to compete with the blow-by from 6 cylinders at 220psi or thereabouts, there's no way that the piddling intake vacuum is going to compete with that. I always assumed that so long as one has a reasonable rate of crankcase evacuation, that should be OK ?

 

Ivor

My experience is with an MGA, a TR4 and a Jaguar MK2. It is on that Jaguar engine that I discovered the problem: when adjusting the carburators, I had the crankcase ventilation disconnected from the airfilter. After about 15minutes fiddeling with the carbs (mostly in idle) I found a puddle of oil under the front crancshaft seal. Of course I did not yet understand the reasons for it. When I then put the airfilter and the ventilation back, the leak did not any more occur. I then did Google quite a lot under the topics "oil leak on engines" and read several reports saying: if you have the slightest positive pressure in the crankcase, your engine will leak "everywhere" , not only at the ends of the crankshaft, but also on the valve cover etc.

My idea was then: if positive pressure makes leaks, then negative pressure must stop leaks.

I bought an electric 12V airpump for inflating swimming gear: this pump has not only a pressure side but also a succion side which I connected to the crankcase ventilation. The hole for the dipstick I pluged with a pressure measuring device. In spite of the leaks at the crankshaft ends I got a depression of about 200mm H2O colomn. And no oil leak at all.

Upon that I built something more professional using a mini-blower 12V with a promised livetime of 1000h. The depression was much less: about 40mm with engine off and 20mm with engine full load. (I had a small plastic tube with a syphon installed in the cockpit, filled with red ATF so I could see the depression by one column going up and the other down, the differnce being never less than 20mm.

The only problem I have with that device, which is installed now in the three cars is that the fan gets oily, because it aspirates a mixture of air and oil mist. I should improve the device in such a way that the oil can run down into the oil pan.

If you are interested, I can send you a picture.

Wilfried

[trfella]

My experience is with an MGA, a TR4 and a Jaguar MK2. It is on that Jaguar engine that I discovered the problem: when adjusting the carburators, I had the crankcase ventilation disconnected from the airfilter. After about 15minutes fiddeling with the carbs (mostly in idle) I found a puddle of oil under the front crancshaft seal. Of course I did not yet understand the reasons for it. When I then put the airfilter and the ventilation back, the leak did not any more occur. I then did Google quite a lot under the topics "oil leak on engines" and read several reports saying: if you have the slightest positive pressure in the crankcase, your engine will leak "everywhere" , not only at the ends of the crankshaft, but also on the valve cover etc.

My idea was then: if positive pressure makes leaks, then negative pressure must stop leaks.

I bought an electric 12V airpump for inflating swimming gear: this pump has not only a pressure side but also a succion side which I connected to the crankcase ventilation. The hole for the dipstick I pluged with a pressure measuring device. In spite of the leaks at the crankshaft ends I got a depression of about 200mm H2O colomn. And no oil leak at all.

Upon that I built something more professional using a mini-blower 12V with a promised livetime of 1000h. The depression was much less: about 40mm with engine off and 20mm with engine full load. (I had a small plastic tube with a syphon installed in the cockpit, filled with red ATF so I could see the depression by one column going up and the other down, the differnce being never less than 20mm.

The only problem I have with that device, which is installed now in the three cars is that the fan gets oily, because it aspirates a mixture of air and oil mist. I should improve the device in such a way that the oil can run down into the oil pan.

If you are interested, I can send you a picture.

Wilfried

 

 

Sounds like a plan for these leaky gearboxes

[foster461]

If you are interested, I can send you a picture.

Wilfried

 

Wilfried, when you get a chance a picture would be good. It would be interesting to see how you hooked this up.

 

Stan

[Wilfried]

Wilfried, when you get a chance a picture would be good. It would be interesting to see how you hooked this up.

 

Stan

Here are some pictures from MGA and TR4

Wilfried