I have been offered a car with dry sump lubrication and I'm told that
the engine does not need a breather as all air is scavenged back to
the tank. I always thought engines had to breathe. Can anybody help?

"Helen" <moon27.helen (AT) googlemail (DOT) com> wrote

My old triumph motor bike had dry sump lubrication and it also had various
breathers( and oil leaks). Whilst it is true that the return pump pumps 2 or
3 times the amount of the delivery pump so that all the oil and some air is
returned to the oil tank, it is a very poor way of allowing an engine to
breathe. Various vapours including water , need to be removed from the
engine and this is normally done by ventilating the crankcase to the outside
,normally to either the air filter or the inlet manifold , you really dont
want the vapours back in the oil tank , you need to get rid of them .
Lou Bricant

"Helen" <moon27.helen (AT) googlemail (DOT) com> wrote

Interesting. What car would that be?

You're right though, it needs a breather as just pumping the oil (and it's
only oil, even though it might be somewhat aerated) back into the oil tank
isn't going to do much to alleviate air pressure variations in the crankcase
due to things going up and down and round and round.

Ron Robinson

On 26 Feb 2007 03:24:48 -0800, "Helen" <moon27.helen (AT) googlemail (DOT) com>
wrote:

No, the scavenge pump only pumps oil, not air. Although it will be
designed so that it happily handles air or a mixture when cornering,
this doesn't remove the need for a breather system.

What is it, BTW ?

Thanks for all your help.
The car is a Bentley with the engine tuned for racing.
There is a breather hole in the filler cap of the oil tank. I'm
assured that this will be enough ventilation, but I'm not sure as its
only 5/16ths of an inch. The original crank case breather was through
the oil filler cap, but this has been blanked off as it's now a dry
sump. Do you think it should have better breathing than this?

"Helen" <moon27.helen (AT) googlemail (DOT) com> wrote

What sort of Bentley? There are several different types, built in several
different places, but I would have thought that if the engine had been
properly 'tuned for racing' there would be a crankcase breather and it would
lead into a catch tank of adequate capacity to meet with the approval of the
scrutineers. Take a pipe from where the oil filler used to be and run it to
a suitable sized can which is vented to the atmosphere.

Ron Robinson

"Helen" <moon27.helen (AT) googlemail (DOT) com> wrote

from Alan Padgett - and what he doesn't know about building Bentley
engines for racing really isn't worth knowing.

Please tell me it isn't one of those hideous Mk VI specials...


--
Kevin Poole
**Use current month and year to reply (e.g. feb2006 (AT) mainbeam (DOT) co.uk)***

.....No, its an 8 litre WO Bentley.
It's the size of a small steam engine and it's a real monster! Like
all monsters it belches smoke and fire, and the roar is enough to
burst any unsuspecting ear drums within a radius of 50 yards. (I have
may have empoyed just a little artistic license here!)
I'm visiting it this weekend with all your helpful comments under my
belt, and well, we'll see .....
Thanks to everyone who has posted so far.

"Andy Dingley" <dingbat (AT) codesmiths (DOT) com> wrote

Rubbish, the scavenge pump pumps a mixture of air and oil back to the
holding tank, where the air is allowed to rise out of the oil. The engine
sump is connected to the holding tank so a vacuum doesnt form in the sump.

Tim.
..

"Tim.." <the.farm.no (AT) spam (DOT) btinternet.com> wrote

You may have seen a system where the crankcase was connected to the oil tank
by something other than the oil return pipe, but in many years of dealing
with dry-sump racing cars I haven't, but then most of the ones I dealt with
had the tank at the opposite end of the car to the engine. If they are
close to each other, yes, you could perfectly well run a pipe (not the oil
return pipe, a separate breather pipe) from the crankcase or the old oil
filler to the air space in the oil tank. Talking of which, it's a good idea
to use some sort of centrifugal arrangement for separating the oil and air
on their return to the oil tank.

Ron Robinson