Crankcase Breathers Options

[McMark]

I was looking at the factory manuals and talking with someone about crankcase breathers. We were talking about breather setups for carbs specifically. And I realized as I was looking at the breather diagram that it appears that the breather ports on the heads were included to supply extra air to flow through the engine case. And then I read this little snipped in the manuals which seems to support my thought:

Crankcase ventilation has been considerably improved in the engine by ducting fresh air from the air filter. This modification reduces crankcase condensation and icing at low outside temperatures.

So following that logic...
If the crankcase breather (at the oil filler neck) isn't connected to a vacuum source, then the ports at the heads should/could be plugged instead of connected to a breather box.

Thoughts? Contradictions? Agreement?


I realize people have been connecting breathers all sorts of different ways and most work just fine. I'm more interested in the theory aspect, and refining an 'ideal' installation since we already know many ways to 'make it work'.

[SirAndy]

From my limited experience the head vents *suck* air until you get to higher rpm (5k+), at which point there seems to be enough pressure in the case to reverse the flow.

That was on my carbed 2056 ...
(IMG:style_emoticons/default/bye1.gif)

[Beebo Kanelle]

I always want the crankcase ventilation to be just that. Venting the crankcase. I'm afraid that the venting of the heads inhibits oil drainage back into the crankcase and may, in fact, exacerbate oil loss.

Just my 2 cents...

[michael7810]

I had crankcase and head vents tied directly into my air filter lids until recently when I installed Gold Wing air filters. Now I tied the 2 head vents together with a single hose (what I read from Jake Raby a while back) and vented the oil filler housing overboard (thru tin under the engine). Eventually I want to get a breather can for the oil housing vent. I drove the car to ~1800 miles to WCR and back with no adverse effects that I know of. Didn't use any oil that I could tell and I had expected it to use about as quart based on previous trips with the old configuration. I'm leaving tomorrow for RRC and that will be about 2K miles with the new configuration. I'll report back if the results were not the same as WCR. I have a 1911cc with webers.

[McMark]

I always want the crankcase ventilation to be just that. Venting the crankcase. I'm afraid that the venting of the heads inhibits oil drainage back into the crankcase and may, in fact, exacerbate oil loss.

Just my 2 cents...

It could inhibit drainage if there is no vacuum source on the breather, since that configuration would make all ports into exit ports.

But on a plenum based engine with the case ported to manifold vacuum, are would almost always be sucked in the heads and flow down the pushrods tubes to the case, which would aid drainage.

To really compare anecdotes we need some pertinent info:
1. Heads ported? Where to?
2. Case ported to vacuum? (Air filters are not vacuum, ever)
3. Functional PCV valve?
4. Stock-ish or Wild engine?

[914_teener]

(IMG:style_emoticons/default/agree.gif)

[yeahmag]

In my last build, Jake's recommendations at the time were to close off the head vents and run a larger vent from the chimney. Now, I'm dry sumped too, but a -10AN modded "chimney" to a breather is all I have for the motor.

[falcor75]

http://hamheads.com/type4-test.php

Here's some info on it....

[SirAndy]

http://hamheads.com/type4-test.php
Here's some info on it....

Interesting ...
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[McMark]

I think I had read that before, but it was a good refresher. Unfortunately, it doesn't address a stock type system where the breather 'chimney' is connected to manifold vacuum.

I would agree with Jake and Len for non-vacuum-breathers. But if the filler neck is connected to manifold vacuum, the head ports should be connected to filtered air supply.

[ottox914]

I think I had read that before, but it was a good refresher. Unfortunately, it doesn't address a stock type system where the breather 'chimney' is connected to manifold vacuum.

I would agree with Jake and Len for non-vacuum-breathers. But if the filler neck is connected to manifold vacuum, the head ports should be connected to filtered air supply.

Sounds about right to me. On my 2056 with ITB's I've got the heads plugged per Len and a single line off the filler neck to a tangerine racing catchcan. No issues noted.

[914_teener]

I think I had read that before, but it was a good refresher. Unfortunately, it doesn't address a stock type system where the breather 'chimney' is connected to manifold vacuum.

I would agree with Jake and Len for non-vacuum-breathers. But if the filler neck is connected to manifold vacuum, the head ports should be connected to filtered air supply.

I.d agree in a stock aystem. Manifold vacuum equalizes the pressure in the rocker chamber by drawing filtered air into the rocker chambers up and out the chimney and into the intake to be burned.

Interesting that they tested it with a dry sumped motor.

My quess is that it was equalizing in the chimney depending on the crankcase pressure.....and if aerated enough into the puke can.

[McMark]

Just found this in the 1975 Emissions book that came in the glovebox with the operation manual. Oddly it shows the filler neck vent connecting to the air cleaner, and the head vents connecting to what appears to be the plenum, which is completely backwards to how we know the system is hooked up. But it does show that the air flow is intended to flow into the heads and out of the filler neck.

[worn]

Just found this in the 1975 Emissions book that came in the glovebox with the operation manual. Oddly it shows the filler neck vent connecting to the air cleaner, and the head vents connecting to what appears to be the plenum, which is completely backwards to how we know the system is hooked up. But it does show that the air flow is intended to flow into the heads and out of the filler neck.

I like how they show air going two opposite directions in the same line. Might it be that they expect the air to oscillate and eventually particulate matter would be sucked into the intake?

I also am wondering about the term flash arrestor used for the T that connects the two rubber lines from the heads. Is that so a backfire cannot ignite the case vapors?

[worn]

Just found this in the 1975 Emissions book that came in the glovebox with the operation manual. Oddly it shows the filler neck vent connecting to the air cleaner, and the head vents connecting to what appears to be the plenum, which is completely backwards to how we know the system is hooked up. But it does show that the air flow is intended to flow into the heads and out of the filler neck.

Also an anecdotal evidence is that when I initially plugged a set of earlier 2.0 head vents the D-jet ran fine. But when the plugs popped out (undetected by me on the way home from Rt66 I had oil all over the place running at 3000 RPM. So I am thinking there wasn't a lot of suction going through them. At least as I hooked up the oil breather, which went to the air cleaner I think.

[ChrisFoley]

Just found this in the 1975 Emissions book that came in the glovebox with the operation manual. Oddly it shows the filler neck vent connecting to the air cleaner, and the head vents connecting to what appears to be the plenum, which is completely backwards to how we know the system is hooked up. But it does show that the air flow is intended to flow into the heads and out of the filler neck.

You're looking at those diagrams all wrong Mark. The passages leading to the heads are intake runners not rocker box vents.
The only crankcase ventilation in both pics is the one at the filler tower.

[McMark]

Just found this in the 1975 Emissions book that came in the glovebox with the operation manual. Oddly it shows the filler neck vent connecting to the air cleaner, and the head vents connecting to what appears to be the plenum, which is completely backwards to how we know the system is hooked up. But it does show that the air flow is intended to flow into the heads and out of the filler neck.

You're looking at those diagrams all wrong Mark. The passages leading to the heads are intake runners not rocker box vents.
The only crankcase ventilation in both pics is the one at the filler tower.

Your right. That's stupid. (IMG:style_emoticons/default/dry.gif) (IMG:style_emoticons/default/ar15.gif)

[r_towle]

So, what setup for carbs would you suggest to suck the most oil out of the valve covers and back into the case?

[IronHillRestorations]

I ran hoses from both head vents to a T and to one carb. I found some cloth braided hose at NAPA that looks like it could've come from the factory, and not too expensive

[r_towle]

But what method works the best?