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Proper crank-case venting with mods - 78 Midget

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lbc_newbie

lbc_newbie

Jedi Warrior
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I have a 78 Midget with a 1275 (not a 1500) and need to know the proper way to vent the crank-case. I have a Weber conversion and a Pierce manifold and K&N filter with 1/2" barbed connecting point. There is an open connecting point on the timing cover (funky canister looking thing). Does that go to the vent on my air-cleaner? I do not have any smog on the car, no PCV valve either. I have the valve cover vented to the charcoal canister. I had oil blowing out my dipstick and found I needed to vent the crank-case, but cannot figure out how to do it properly with the mods that I have.
 
That cannister thingie is a kinda-sorta "swash plate" device to cut down on the oil escaping. If running it to a separate container with a piece of hose is possible, try that first. If it still "pushes" oil you may need to introduce some "negative pressure" by running it to the air cleaners... tho with what you describe it'd be better to not suck oil to the intake. The charcoal canister would definitely be a restriction and could cause the condition.

Another possibility is: crankcase pressure is above normal due to worn rings... but we won't worry over that until other things have been tried.
 
On most 1275's it went to the air intake to give a bit of vacuum to the crankcase.
 
Newbie
Where are you in Seattle- I'm in Renton.
Are you in the MG club?
I agree that you need to hook up the PCV, otherwise you will leak oil like a pig.
Bill
 
Check out the web:
https://www.mgccnwc.com
RickB and I both attend the Bellevue meetings

Good club, several Midgets (one Sprite)

For the PCV I would recommend trying to hook the canister at the front of the engine to one of the air cleaners (or if your Weber manifold has a port for it connect the canister to a generic PCV valve and into the manifold port)

This will at least get you started on stopping the oil leaks.

Bill
 
Billm said:
(or if your Weber manifold has a port for it connect the canister to a generic PCV valve and into the manifold port)
Bill
Click to expand...

I had to drill and tap a hole in my Pierce intake, right under the carb, outboard side, to get some good vacuum to the valve cover. The hose to the air cleaner didn't provide enough vacuum.
 
I'll jump in here because I'm having similar issues with mine. I hooked my crankcase ventilation back up this weekend. I went from the timing chain cover breather up to the same Weber air filter inlet that lbc_newbie is talking about. I did this however, with NO PCV valve, and my car smokes pretty good now. What I'm wondering is if I can just buy an off-the-shelf PCV for my setup instead of paying the $75.00 that I see one of the big suppliers wants? Do different PCV valves open at different manifold vacuums and/or crankcase pressures or can I use whatever I can make fit?

Also, while we're on the subject, perhaps someone can explain the reason and function of the PCV valve. Is it closed under heavy vacuum (idle) to prevent sucking too much fumes and therefore smoking and then opens at RPM when more crankcase pressure would be present? That's the only way that makes sense to me. Thanks!

JACK
 
The purpose of the PCV (positive crankcase ventilation) is to keep a backfire from getting into your crankcase and blowing it up. All it does is allow pressure to pass one way (from the crankcase) and not the other (into the crankcase).

To prevent oil from entering the intake, you may need to buy or build an oil catch can.
 
Is there another source that it can be routed to other than the intake? I've seen images where only a breather is installed with a filter on it, some have it going from the timing cover to the valve cover, others have far too complex systems to create on my engine. I just want to know what works best without all the smoke! Thanks for jumping in on this, Jack.

Ed
 
Hey Ibs newbie, I have a 78 1500 and just went through all this as I put the Weber conversion on my midget as of late. All of the emissions items on my car are gone so my response is going to be a bit less complicated. By the way if your wondering, the car runs great with all the emissions items removed. It depends on the state you live in if you can get away with taking it off. Anyway, under the air cleaner on the weber they give you a plastic hose barb to connect a hose to. Run air hose from this barb over to the hose connection on the side of the valve cover. Now this alone will not remove the oil blowing out of the dipstick so you need to tie in a 3 way hose barb to allow a 3rd hose in the network. This hose was connected to an oil breather which I picked up at Autozone for $20. After that all my oil issues were resolved and it runs good.
 
If you pull vacuum on the oil sep canister on the timing cover, you should probably fit a pcv valve in line. If you want to try and avoid an oil catch can, then you might try reducing the line diameter so that it pulls less volume. I think that makes sense. Let me go get a cup of coffee and come back.
 
hey Sweendog,

Am I understanding this correctly. You have a vacuum source, the barb under the carburetor, teed into the crankcase vent, and a filter exposed to atmosphere? If this is so, please remove the filter with the engine running and check for vacuum at that fitting. Sounds like you are running an open vacuum, which will lead to leaning out, etc..
 
So here is what I found from a race friend of mine...

Edward: On my race car I run a length of 1/2 inch heater hose from the breather to a "catch can" which is nothing more than a small container which holds any oil that comes out. You could run a hose from your timing chain cover to the same can. Almost any container would work. Mine is mounted up high on the firewall. You need to be able to drain it periodically. The catch can is a long aluminum cylinder mounted to the firewall. You can buy catch cans fairly inexpensively on ebay. Just search on "catch can" in ebay motors parts and accessories.

I'm thinking I'll try this out... nice, affordable option.
 
I am going to disagree with Morris-
The PCV valve should(and will) stop a backfire from going into the crankcase but it also restricts the volume of air going from the crankcase into the intake. As someone back a few notes said it allows "wide-open" air flow when there is low-vacuum in the intake (at higher car speeds) but only allows partial open air flow during high manifold vacuum (ie. at idle). This gives you a more constant air draw and allows less oil to be drawn up into the intake.
Any generic PCV valve with 1/2" fittings from the chain stores will work perfectly.
Bill
 
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