inlet / breather valve
inlet on the 2CV motor is more than just a funnel to fill in the oil.
The unit controls the pressure inside the crankcase. Inside the
cylinder the breather valve found its home.
It is quite easy to explain the necessity of this valve. Imagine the
pistons are just at the upper dead center. This means one cylinder
just fired. The explosion drives the piston down. Via the crankshaft
the other piston is also pulled down. As long as both pistons were at
the upper dead center we had a certain amount of air inside the
crankcase with atmospheric pressure. With the pistons coming down the
space inside will be reduced by about 600 cc. This would increase the
inside pressure what would make the pistons to fight against this
increasing pressure. The result would be counterproductive. To avoid
this effect we have the breather valve. It is located inside the
cylinder of the oil inlet. When the higher pressure wants to build up,
the valve opens and lets the motor breathe out. Once the pistons reach
the lower dead center the valve closes again. The pistons now continue
upwards what gives us a little under pressure inside the crankcase.
When the motor breathes out it will also take some fine oil out of
the motor. The crankshaft splashes into the oil sump in every cycle.
So the oil sprays everywhere. The air inside the crankcase contains a
fog of microscopic drops of oil. When the motor breathes out this oil
fog goes with the air. If now this air would be released into the
engine compartment, pretty soon a fair film of oil would cover
anything (including the front brakes).
To avoid this the air is led into the air cleaner. For this we have
the hose between the oil inlet and the air filter housing. The
carburetor will now suck the oil drops in and the motor burns it.
The breather valve is designed very simple. It is just a flat layer
of rubber what lies on top of a flat panel covering holes. If now the
pressure on the underside rises over the pressure on top the rubber
will just be lifted up. The over pressure will escape. When the
pressure on the underside drops down the rubber is pulled down sealing
off the holes.
Open oil inlet
with breather valve
years and miles the rubber turns hard or some dirt settles between the
rubber and the panel. Therefore the under pressure cannot build up.
The result is that the motor pumps out about 600 cc of air in every
cycle. So far no problem, but remember the fog of oil. When a lot of
air is pumped out, the amount of oil going with it also rises. In the
air cleaner housing the oil condensates.
In a good motor the "basement" under the air filter is oily
and dirty. If the breather valve doesn't work proper you will find a
lot of oil in the air cleaner. As long as the motor runs it pumps oil
into the air cleaner. When the motor stops the oil will run back into
Anyhow - if you find a lot of oil in the air cleaner it doesn't
necessarily mean that the breather valve is defective. It can also be
an indicator that the compression isn't good anymore, i.e. if the
piston rings are broken or worn some pressure from the explosion will
find its way into the crankcase. This overpressure will be pumped out
via the breather valve transporting the oil into the air cleaner.
If the breather valve is defective the whole oil inlet assembly has
to be replaced. A repair is normally not possible. My attempts to wash
out the oil inlet cylinder with solvent fluids did not work.
The assembly is attached to the crankcase with two 7mm bolts. The
hose to the air cleaner is simply to be pulled off. Before you
disassemble the oil inlet it is recommended to loosen up the holder
for the alternator.
When the bolts were removed you can simply pull off the oil inlet.
Mostly the seal between the crankcase and the foot of the oil inlet
rips apart. To avoid anything from falling through the hole into the
crankcase you should push some clean tissue paper into the hole.
Before the new oil inlet can be installed the rest of the old seal
has to be removed from the crankcase. Use a sharp tool to scratch it
off but don't hurt the aluminum surface.
To install the new oil inlet you have to use a new seal. I always use
some liquid seal to compensate little scratches on the surfaces. This
stuff also holds the seal on the foot of the oil inlet. Quite often
the little rubber hose between the foot of the oil inlet and the
dipstick turns hard. This makes it impossible to seal off again. To
avoid an oil leak I put some liquid seal on the outside of the little
pipe on the oil inlet. The hose pushes back the excessive sealant
material when you push it in. This sealed off every motor where I
replaced the oil inlet. It is much easier to use liquid seal then
clamps on the ends of the hose. It would be very hard to reach the
clamps to tighten them when the oil inlet is installed.
When you remount the new oil inlet (Don't forget to take out the
tissue paper from the hole) put the foot in the right place and insert
the bolts (Don't forget the holder for the alternator). It is very
tricky to get the bolts in the right position. Due to the shape of the
oil inlet it is hard to get the bolts in straight. If you now use a
tool to force the bolts in, this will destroy the threads in the
crankcase. So it is recommendable to put the bolts in just by using a
11mm socket and extension. When the bolt is almost all the way in you
can use a ratchet.
When the bolts are tight and the hose to the air cleaner is connected
you are done.