1275 Marina engine with active crank case ventilation

[MMT1968]

Hi there,

I rebuilt a 1275 Marina engine and tuned it seriously to a powerful street engine for my Traveller. It has raised compression ratio to 10.3:1, a fully ported head, a Kent 266 camshaft, twin HS4 carbs and a big bore Maiflow exhaust. As it was difficult to set up a good and functional crank case ventilation and several tried solutions failed I ended up in setting an active crank case vetilation system by using an electric vakuum pump with an oil catch can following some suggestions in US V8 boards. That works perfectly. The engine is now loosing not a single drop of oil and to my subjective experience is running a bit better.
Different from the US suggestions I used a Bosch secondary air pump. The main advantage of this is that it is a kind of turbine system though leaving the ventilation pipe open to athmosphere if the pump is not running for any reason. That way there is always some ventilation of the crank case. The pump is producing a negative pressure to the crank case and sucks the vapour out continuously. I added a PWM controller to regulate the revs of the pump motor to adjust the suction level.
I also added a Land Rover flame trap to prevent oil being sucked into the pump. The outlet pipes of the pump are lead underthe car. When the system and the engine is running the vapour being sucked out of the crank case is visble showing that it works well.

Chris

[svenedin]

Very interesting. I am a believer that so many A-series engines leak oil due to neglected or misunderstood crankcase breathing. I managed to get my 1098 to a state where it will leak just one drip of oil on shutdown from the rear scroll. This is the best that can be achieved with the scroll oil control because it is not throwing oil forward when the engine is stopped and there will always be a little residual pressure.

I am also a believer that there is elegance in simplicity. Did you try to get the engine to breathe using a Smiths PCV valve on the inlet manifold or with a breather type carburettor (a later SU with a breather port)? You could have a set up where there is a tappet chest oil separator and a breather rocker cover connected via a Y-piece to vacuum or there are various other ways to have 2x breathers.

Although they are very expensive, I do admire and covet this beautiful replacement front plate assembly: https://s-can.co.uk/product/timing-cove ... rris-1000/ If money was no object I would get one!

Stephen

[philthehill]

A very good installation - but in my honest opinion total overkill.
If a 'A' Series is assembled correctly it will have no excessive crankcase pressure that leads to oil leaks or drips via the rear scroll. My 1380cc full race (Marina 'A' Plus based) engine has only the timing chain cover canister breather, a breather on the fuel pump aperture and a pipe from the rocker cover and it has no excessive crankcase pressure, leaks or drips from the scroll.
The front cover assy in the link above is very nice but again if the engine is assembled correctly there will be no leaks from the front of the engine.

[MMT1968]

Hi Stephen,

….elegance in simplicity…, a nice interpretation of choosing the cheapest option even if it’s a pre war solution, very common in BMC cars.

Back to topic.
Yes I tried a smiths PCV valve at the inlet maifold but that didn’t work. The vacuum to the crank case was much to strong and oil gut sucked into the combustion chambers producing a huge cloud of smoke. As my carbs don’t have a breather port there is no connection for the breather pipe possible there. I also tryed the connection to the air filter housing that didn’t work eigther. Simply leaving the pipe open to athmosphere was not sufficient. So I ended up with the active system as it is now.

Chris

[MMT1968]

Hi Phil,

You’re right, total overkill. But it works. And as the scoll on my crank shaft is so badly worn - you have seen a photo earlier- there was no other solution than mounting a rear cank seal which was difficult to get it sealing well due to the courious way of mounting it in a Marina/Ital engine. The engine has been mounted carefully and right to specs in any case, i.e. ring gaps at 0,25mm aso, and the crank case pressure I see now may be reduced after running in.

Chris

[svenedin]

Hi Stephen,

….elegance in simplicity…, a nice interpretation of choosing the cheapest option even if it’s a pre war solution, very common in BMC cars.

Back to topic.
Yes I tried a smiths PCV valve at the inlet maifold but that didn’t work. The vacuum to the crank case was much to strong and oil gut sucked into the combustion chambers producing a huge cloud of smoke. As my carbs don’t have a breather port there is no connection for the breather pipe possible there. I also tryed the connection to the air filter housing that didn’t work eigther. Simply leaving the pipe open to athmosphere was not sufficient. So I ended up with the active system as it is now.

Chris

Ah I see. Perhaps the PCV was not working properly or there was no mesh in the oil separator to catch the oil mist. It is supposed to keep the vacuum fairly constant. At idle when the engine vacuum is high the valve should be almost shut but when the engine is under load and the engine vacuum is low the valve is wide open. When a PCV malfunctions it is worse than useless; it actually makes the engine leak more. When mine went wrong there was oil leaking from everywhere!

Stephen

[svenedin]

A very good installation - but in my honest opinion total overkill.
If a 'A' Series is assembled correctly it will have no excessive crankcase pressure that leads to oil leaks or drips via the rear scroll. My 1380cc full race (Marina 'A' Plus based) engine has only the timing chain cover canister breather, a breather on the fuel pump aperture and a pipe from the rocker cover and it has no excessive crankcase pressure, leaks or drips from the scroll.
The front cover assy in the link above is very nice but again if the engine is assembled correctly there will be no leaks from the front of the engine.

Interesting. So you had a set up with 3x breathers? My standard 1098 has one (tappet chest breather) but I am considering adding in a breather rocker cover and connecting with a Y-piece.

Stephen

[philthehill]

Yes three breathers (still) all discharging into a catch can which has never received a drop of oil.

[MMT1968]

So do some Minis. One breather on the crank case and another one at the rocker cover.

I have two pipes led in one and then connected to the flame trap and from there to the catch can. One coming from the canister on the timing chain cover, the other one from the fuel pump aperture. When I tested the pipe connected to the air filter housing the oil leaked almost everywhere. The PCV valve was a completely new one but didn’t work either. As I read in several posts the BMC-A engines, specially the bigger ones, should be run best with -0,2 bar crank case pressure I decided to build that vacuum pump system and this has proven as beeing effective. So I‘ll stick with it even It’s a bit overkill.

Chris

[Classiccars]

I had a lot of trouble with mine on a traveller with an ital 1275 engine.Too much oil was pushing out of the breather cylinder for a pcv valve.I put the pipe from rhe breather cylinder to the rocker cover with a pipe pointing up to air.The oil now can't go to air as the pipe points up it goes to least resistance back to the engine via the rocker cover.Now I can drive and keep my oil in the car.Not ideal but it seems to work.

[MMT1968]

I guess there might be a lot of solutions therefore that help solving the problem more or less. I just wanted to show another but working solution for those who are facing similar problems than myself.
At last I got tired of pulling the engine out to reseal the rear crank seal again and again. So I looked for a solution that would last. PCV valves are mainly mounted to reduce air pollution. And if they don’t work they are more than useless. My Jag XK120 has a simple hose from the chain cover leading under the car that is open to atmosphere. That works good enough in that case.
No one ever cared about pollution in the 50ies and 60ies when these cars were built so why should I do now. I‘d never think about mounting a catalyst system to my Traveller‘s exhaust either.
But in my case the open hose surely reduced the crank case pressure but didn’t stop leaking oil. So I ended up with the „vacuum-crank-case-evacuation-system“, VCCE, as I like to name it.. Good enough that it works well to keep me from being frustrated as I was.
Overkill yes or no, I just like to drive any of my cars without watching the oil pressure warning light steadily with an oil canister in the boot and have fun.

Chris