Carterpressure of an Honda VF400F

All 4-stroke bikes I ever owned had some contraption
that made the pressure in the carter (is that English?
maybe should call it 'sump') slightly below ambiant. The
effect is that oil will not be forced out, but instead be
retained in the sump. (The Harley vintage1927 did not
have such a contraption because I kept on filling
the oil tank with oil ;-) *Gawd.. everytime I think
about that one-cilinder, water comes to me eyes. Not
because my love for HD, but that machine was sold for
100 guilders (50 US dollars!) many years ago.

I currently own a Honda VF400F. The manual is not clear
about any 'contraption' that would keep the sump pressure
lower than ambient.

A week ago I blew out an oil seal and made a nice 4 mile
trail of oil on the road (I'm waiting for the environment
police because all they need to do is to follow that trail
back to my back yard).

That oil ring (seal) is for the clutch actuator pin (hydraulic
clutch actuator on the left, clutch on the right hand side of the
engine, so that '8 millimeter pin' traverses from the outside left
to the inside right of the engine.)

That seal is hard to replace. It is mounted from inside the
sump (you need to take the whole engine apart) and retained
by a rim that prevents it from blowing out (and prevents me
to pull out the old seal and insert a new seal from the outside).
This gives me the idea that the sump has a pressure that is
higher than ambient. The seal is blown outward (that is why there
is a rim).

I 'filed' out the rim, inserted a new seal (simmer ring as we name it)
from the outside and fixed it with some glue and a homemade
retainer to prevent it from being blown outward.

I now have small oil leakage (some drops) that seems to come
from the seal/pin area, but I cannot tell if that really is the spot
where it leaks.

Question:
*********************************************************
Is it standard for the VF400F to have overpressure in the sump?
*********************************************************
If not, I have to take the engine apart and go for oversize pistons
and rings (or a kinked tube going to the air intake).


Rob.

 

There really is no such device, bu motorbike engineers are very aware
of pumping losses inside the crankcases as pairs of pistons move up and
down. Engineers have been designing ports between cylinders to allow
the air to move around without being compressed.

But the piston rings probably have enough "blow by" to pressurize the
crankcase by a few PSI after the engine has a few thousand miles on it.


There is probably some kind of oil vapor separator on the crankcase or
on the valve covers. It's usually a wire mesh that is cooler than the
oil vapors, so it condenses the oil and it drips back into the engine.

If you really want to try to reduce crankcase air pressure, you could
make up a road draft tube from the crankcase to the road. Cut the
bottom of the road draft tube on a 45 degrees bevel and aim the bevel
to the rear. That causes turbulence when the motorbike is moving and
sucks vapors out of the engine.

Another way is to get some large diameter plastic tubing and run it
into the low pressure area behind the motorcycle.

Or, you can run the breather hose into the air box. The air pressure
isn't that much lower than ambient in the air box though.

 

Hi,

Thanks FB.

I should have told: The VF400F engine is basically the same engine
as that of the VF500, VF750, VF1000 and (I think) the Honda
Magna. It is a 90 degrees V-shaped engine, has four cilinders, and
each pair of pistons move simultaneously up and down.

There is such a 'device' that keeps crankcase pressure
low. Very simple: A disk with a hole. Or just a piece
of sheet metal that we call butterfly-valve.

My former BMW's (R20 thru R50) and even the Ural-crap all had a
breather to the outside world. I cannot remember how my other bikes
were built, because you only look at stuff when it malfunctions, and
breathers never gave any trouble. The beamers did not either,
but you could hear them puff. The Ural was a totally different story...

The breathers were just a piece of metal pipe running from the
crankshaft bearing (front end) downwards to the outside world.
On the crankshaft there was a rotary shutter (a disk with a 'long'
hole in it) that opened the breather at the moment the pistons
went inwards (down) but closed when the pistons went out (up)
so that --on average-- the sump pressure was a bit below
ambient, and certainly not higher than ambient, which keeps the
oil inside nicely.

My VF400F breathes the crankcase by some tubing via an
oil-separator right back to the air box (for environmental reasons).

The only oil seal to the outside world got defective and made
me spill a gallon of oil on the road. And it spat like a fountain.

So I bought a new seal and then, to my amazement, found
that the 'rim I was talking about' prevents the seal of
being blown out. I expected a 'rim' that prevents the seal
being sucked in. Also the position of the seal (rubber lips
inward) tells me that there is/should be overpressure in the
crankcase.

I filed out the rim (opening the engine is too much work),
applied glue to the seal, waited long enough to let it
set, started the engine, and the seal popped out like
a cork.

I then made a retainer, so it is fixed in place now, but
all that made me think: Did not Honda make anything
(the 'contraption') to prevent crankcase pressure
building up? The manual does not say anything about it.


BUT...
The advantage of writing a story is that you have to
re-think again. I only just did........
I better have a look at the breather tubing (kinked?), the
oil seperator and all that stuff.

Rob.

 

I suppose that the true intent of such breather valves is to keep cool
moist air from entering the crankcase and causing parts to rust while
the machine sits unused over the winter.

Kawasaki used reed valves on the cam cover. They might have been to
prevent backfires from following the oil vapors back to the crankcase,
but, since I never owned one that had the reed valves I never studied
it.

 

......................

.............................

I think you have your answer right there. Open breather =
unacceptable to exhale oil mist. Breather connected to air
box = let's keep pressure balanced to prevent moisture
and dust entering the engine.

I have seen oil seals that were mounted from the outside
(countershaft sprocket, gear change) on engines without
regulated breathing and as long as nothing is really wrong
I don't think they will be forced out. The reason for your
clutch rod seal being restrained the way it was has to be
something else.

 

This subject can be closed. I found the answer.
Thank you all.
Like OH wrote: It has to be something else.
Sometimes you need someone to tell you that you
are following the wrong trail. Thanks OH.

Well it *is* something else.

I took out the oil seal and had a long peek in the 25mm
bore it is in. Then I saw a little hole in the bores side
(where oil spits out) and saw a ball bearing a bit deeper in
the bore.
I wondered: "What's a ball bearing doing there?"

After long thinking, I realized that the primary gear shift axle
is sitting there, and that it is a hollow axle (the clutch pin goes
all the way through it to the clutch at the opposite end).

The sliders and gears on the axle need lubrication. Some
have small holes perpendicular to the axle, which also has
small holes at the same spots.

Because I cannot draw it, from left to right:
Seal-- oil pressure--hollow axle

So it is not the crank case pressure, but it is the oil pressure
that pops out my oil seal.

Like my late dad used to say: "Bikes are simple things. It can
only be a mechanical, electrical, or fuel problem."

I can add: "But some problems take forever to find".

Rob.