Crankcase ventilation. Part2

In this entry – practical issues, related to replacement of crankcase ventilation.


For N43/N53 engines, the crankcase ventilation valve is part of the valve cover, which means – in case of the damaged membrane, the valve cover has to be replaced. Price of this spare part is EUR 400 .. 450.

Accordingly, the question “is it possible to replace only the membrane” is very logical.

Yes, several manufacturers offer DIY products, which are intended to solve this problem.


For example (N53 series engine):


a) full set (cover and membrane):

b) membrane:

2. (products similar to Bersa products, description of products – identical):


In my e-mail very often I receive complaints regarding these products, so I performed the small experiment.

At first – I purchased several sets of each product (this time I chose production of Bersa). After some time vanos-BMW sent and example for testing purposes too.

At second – I evaluated several repairs, performed by my acquaintances and helped to solve the problems – so to speak, I got acquainted with the situation in real conditions.


Conclusion – there are several significant nuances, which have to be taken into account. What kind of nuances? Read on!


Here you can see products of Bersa tools. On the left – membrane, on the right – full set (membrane and valve cover).

And here is the first surprise (actual for both manufacturers) – membrane is just inserted in valve cover! And nothing has been done to ensure, that the connection “membrane – cover” would be airtight.

The first basic thing, which has to be taken into account (but which is not described in the instruction) – the membrane has to be glued to valve cover! This gluing has to be airtight! If it’s not done, the air is sucked into the inlet manifold via ventilation hole. This air is not measured by air mass measure sensor, and as result, the engine has incorrect and unstable offset type adaptations, the idle can be uneven, misfires can appear, also persistent vibration in idle, errors regarding fuel trim etc.

(1) Body

(2) Rubber membrane

(3) Spring

(4) To intake manifold

(5) From oil separator (crankcase)

(6) Ventilation hole

Marked with a red arrow: unacceptable airflow from ventilation drill to intake manifold.


In the image, marked with a red circle – ventilation hole for Bersa product.

Ventilation cover for Vanos-BMW product.

Attention – when gluing the membrane, make sure, that the ventilation hole is not covered! After gluing check, if the membrane moves easily, allowing the extra air to flow out via the ventilation hole.

When the membrane is glued, make sure, that the connection is airtight. Cover the ventilation hole with a finger (from outside of the cover) and try to move the membrane. If you don’t feel strong resistance, you have to find the places, which are not airtight.


Second essential thing. These aftermarket membranes are thicker than OEM products (this is not bad – they are resistant) and construction of membranes, produced by Bersa tools, is slightly different from the construction of OEM membrane – membrane, produced by Bersa tools, squeezes the spring bit more. In addition – overall ”height” of valve (air gap when valve is opened) can differ after repair. Due to these obstacles, usually it takes more power to move the membrane, which means, that the valve doesn’t close completely with OEM spring! For valve to work perfectly, as the producer has intended (if the valve doesn’t close properly): the OEM spring has to be shortened – one winding has to be cut off.

After shortening, the last winding has to be bent as shown in the image:

Also, connection ”cup – cylinder head cover” should be airtight.


When the valve is glued and mounted, the performance of it has to be checked.

1. Turn on the engine, don’t press the accelerator pedal (so the engine will work in Homogeneous mode mixture);

2. wait for at least 30 .. 60 seconds, check, if the wide-band Lambda probes are heated up: ../F5/F6

PWM of the wideband probe heating has to be an the area of 30 .. 60 % – it means, that the probes are being heated and are in work order.

3. open the oil refilling cup while observing offset type adaptations and integrators.

Note: for some SW releases (typically for N43 series engines) offset type LTFT are displayed ”after” voltage of control probe (scroll down the fuel mixture menu).

If the integrators and offset type adaptations don’t change essentially (fast), the valve is in working order.

If the integrators are increasing fast (and reaching +30%) and/or offset type adaptations also are changing, the valve has not closed – solve the problem.


Possible causes:

a) the spring is gripping and don’t allow the membrane to cover crankcase ventilation;

b) the spring is too strong, it has to be shortened;

c) membrane is not airtight via perimeter, the air, which flows via ventilation hole, presses the membrane in inclined position – the membrane doesn’t cling to the crankcase ventilation outlet and don’t close it;

d) ventilation hole is blocked – unblock it.


If the engine had problems with the crankcase ventilation before, and due to this defect the error messages regarding, for example, fuel trim, obligatory:

a) delete old adaptations;

b) re-adapt the engine. More information read here.