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Crankcase ventilation
https://www.ausmini.com/forums/viewtopic.php?f=2&t=89312		 Page 1 of 1
Author:  Hanra [ Fri May 01, 2015 8:43 am ]
Post subject:  Crankcase ventilation
Im pretty sure Ive brought this topic up before in someone elses thread, but rather then hijack, Ill make my own.

OK first up..... Is my rocker cover oil cap a vented type? Is air drawn in or pushed out at this point? If it is pushed out, I guess I am also pushing air out of the tube/vent on the top of my Rocker Cover, which, via a hose and T piece, goes directly to both carbs.

I also have a breather fitted at the clutch end. It appears to push air out of that location. If air is being pushed out here and pushed out at the rocker cover...... at what point is air being drawn in????????

So.... Could I buy another Rocker Cover without the tube/vent pipe? Block off the two ports on both carbs? And not effect the crankcase ventilation??? I dont want to blow a seal out... I have no other breathers fitted......


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Author:  drmini in aust [ Fri May 01, 2015 9:24 am ]
Post subject:  Re: Crankcase ventilation
Yes it's a breather cap. As used on Cooper S, Clubby GT, 1275LS and Morris 1100S. It is an air INLET.
That rocker cover is not an 1100S or Cooper S one. They are sealed. I have some here if you need one.
Normally there is a PCV valve on the manifold, and it's connected to that breather can on the flywheel housing for Positive Crankcase Ventilation. Air goes into the cap, and fumes + air out through the PCV valve, into the manifold.
On a road car, this stops smelly engine fumes getting into the cabin.
Author:  Hanra [ Fri May 01, 2015 10:03 am ]
Post subject:  Re: Crankcase ventilation
Thanks Doc. Cant say Ive ever had to much of an issue with fumes in the car with the current set up.

On a standard set up, what is connected to the two ports on either carb???

As you mentioned previously, having these ports directly connected to the rocker cover could be causing a lean condition?
Author:  drmini in aust [ Fri May 01, 2015 10:08 am ]
Post subject:  Re: Crankcase ventilation
Hanra wrote:
Thanks Doc. Cant say Ive ever had to much of an issue with fumes in the car with the current set up.

On a standard set up, what is connected to the two ports on either carb???

As you mentioned previously, having these ports directly connected to the rocker cover could be causing a lean condition?


On a 1275LS, the breather can connects to the vac port on the carb.
On a late Clubby 998 the breather can (on the side cover) connects to the vac port on the carb. Air is drawn into the rocker cover via the charcoal canister. The rocker cover pipe is restricted by a tiny hole. Cap is sealed.
On a Clubby GT the breather can connects to BOTH vac ports on the carbs via a Y piece.
Author:  Hanra [ Fri May 01, 2015 10:13 am ]
Post subject:  Re: Crankcase ventilation
Ok thanks Doc. If I were to get another rocker cover without that vent/tube pipe. Keep my vented Rocker Cover cap on. Block off the ports on both carbs, keep the clutch case vent as it is, do you see any issues with crankcase breathing?
Author:  drmini in aust [ Fri May 01, 2015 10:22 am ]
Post subject:  Re: Crankcase ventilation
Personally, I prefer the original PCV system for a roadgoing 1275.
If you don't want to do that, I would bin the bling filter, block the carby vac ports and just run 2 hoses to a catch tank. Cap would be fine.
Those Bling breather filters have been known to block up.
Author:  Hanra [ Fri May 01, 2015 10:59 am ]
Post subject:  Re: Crankcase ventilation
I dont mind buying a new Rocker Cover if need be without that tube/pipe. But would that be a concern for breathing? Or is the clutch cover breather enough???
Author:  Hanra [ Fri May 01, 2015 1:13 pm ]
Post subject:  Re: Crankcase ventilation
Ive got to buy a pair of retractable seatbelts form Minisport, so perhaps I should also get this rocker cover? And fit my oil cap to it?

http://minisport.com.au/mini-chrome-roc ... h-with-cap
Author:  drmini in aust [ Fri May 01, 2015 1:44 pm ]
Post subject:  Re: Crankcase ventilation
I breather was enough for Mini Cooper S to win Bathurst, 1st 9 places.
Look, you will get varying opinions on here, we all have one.
Some folks say the more breathers the merrier, the bigger the better.
A well known race engine builder gets by with NO breather on one of his engines.
I only had a single breather to a PCV valve on my 1412 stroker, and it was fine. Ditto my 1360, which still revs to 8000.
Author:  Hanra [ Fri May 01, 2015 2:37 pm ]
Post subject:  Re: Crankcase ventilation
I talk your word for it Kev. You have plenty more years of experience then myself!!!!!!! Thanks mate!!!
Author:  1071 S [ Fri May 01, 2015 5:15 pm ]
Post subject:  Re: Crankcase ventilation
[quote="Hanra"]Im pretty sure Ive brought this topic up before in someone elses thread, but rather then hijack, Ill make my own.

"OK first up..... Is my rocker cover oil cap a vented type? "

Yes

"Is air drawn in or pushed out at this point? "

It depends. On a nice healthy engine with breathers attached to ports on the carb you might generate a sufficiently low crank case pressure to suck air in through the cap.

"If it is pushed out, I guess I am also pushing air out of the tube/vent on the top of my Rocker Cover, which, via a hose and T piece, goes directly to both carbs. "

True

"I also have a breather fitted at the clutch end. It appears to push air out of that location. If air is being pushed out here and pushed out at the rocker cover...... at what point is air being drawn in???????? "

Its not being drawn in.. its being forced in past the rings by combustion pressure.

"So.... Could I buy another Rocker Cover without the tube/vent pipe? Block off the two ports on both carbs? And not effect the crankcase ventilation??? I dont want to blow a seal out... I have no other breathers fitted...... "

As Mr Bridger might say...For why?

The breathers are only there to release pressure so the answer is ... maybe.

Having these ports directly connected to the rocker cover could be causing a lean condition?

No, that's why the inlets (inside the carb) are so small

Those Bling breather filters have been known to block up

BTDT

"A well known race engine builder gets by with NO breather on one of his engines.
I only had a single breather to a PCV valve on my 1412 stroker, and it was fine. Ditto my 1360, which still revs to 8000."

This is because both gentlemen have very healthy engines with good ring sealing. As I found out the other day, I have buckets of blow-by (well, the engine is 25 odd years old and has been a daily driver as well as weekend warrior) so I run 2 x 1 inch and 1 x 1/2 inch breather tubes.

The need for (and required volume of) breathers is not particularly determined by engine type/size per se. Its really a factor of the wellness of your rings/bores.... Of course things like compression and revs have an effect.

Cheers, Ian







Kev notes that
Author:  gtogreen1969 [ Fri May 01, 2015 5:19 pm ]
Post subject:  Re: Crankcase ventilation
How about a 5litre catch can?
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Author:  Morris 1100 [ Fri May 01, 2015 5:39 pm ]
Post subject:  Re: Crankcase ventilation
A catch tank is great if you want to inhale fumes as you drive along.
The idea is to reduce pollution, not to modify it so that the driver inhales it.

Race cars use catch tanks because the rules say they have to.
Author:  1071 S [ Fri May 01, 2015 5:53 pm ]
Post subject:  Re: Crankcase ventilation
..And also because inhaled oil reduces fuel octane requiring more retarded timing than might be otherwise achievable....

Cheers, Ian
Author:  gtogreen1969 [ Fri May 01, 2015 8:21 pm ]
Post subject:  Re: Crankcase ventilation
My "catch can" is going as soon as I can get the bungs out of my inlet manifold. Me thinks that someone has taken to them with araldite.
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