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MG MGB Technical - Crankcase ventilation

The PO desmogged my 69 engine (18GH), installed an aluminum valve cover with vented cap and a draft tube from the side cover. He said Brittek recommended that setup. I've talked to Brittek, and they do recommend that setup, claiming that the early engines ran ok like that and that if you blow any oil by, that way it won't gunk up your carbs before you know it.

Never one to leave well enough alone, I found a Smith's MGB PCV valve and decided to install it. ThHe car runs great and has good compression. However, after a hard run for about 30-45 minutes, there was some oil in the PCV valve. I wonder if it would just be from oil that had puddled in the side cover from not previously having sufficient ventilation. After cleaning the PCV valve, I ran the car briefly, alternating idle and reving and didn't see any oil come through.

Any thoughts?
Greg Bowman

Greg: I also have a 69, but with the stock setup, i.e. vented cap, and "Y" pipe connection from the front sidecover into the port on each carb. I assume that you have either blocked these or are using earlier model HS-4s.
My carbs do not get "gunked up" from this setup. I think your approach should work well too. I have noticed that after a sustained high speed running that my oil consumption increased noticeably. Investigating previous threads on the subject of oil use, this does not seem uncommon. My engine, as far as I know, has never been rebuilt and has at least 79,000 miles on it. Under "normal" driving I have not had any problems and the oil use is around 1 qt/1000 miles. FWIW
Andrew Blackley

Greg,
Unless your car is moving there is no air passing over the draft tube tube to pull air through the engine, hence no oil in the pcv valve when revving the car at idle. Personally, I like, and use on my B, an evacupan setup which basically places the draft tube in the exhaust stream and creates a negative pressure in the crankcase when the engine is running.
David

David,
What is an Evacupan? I've never heard of it.
Bill Boorse

Bill,
First off, I take no credit for this idea. It's an old concept that I heard about from a friend who was a national-level drag racer and later I read more on the subject in a book on tuning A-series engines. I also remember seeing a kit advertised by Jeg's or Summit. A 5/8" or so metal tube with a 45-60 degree mitred end is welded (or JB Welded) in the exhaust pipe just downstream of the collector. The tube needs to be inserted about 3/4 to 1 inch into the exhaust pipe at about a 135 degree angle, pointing towards the rear of the car in a fashion such that the exhaust gas passes over the mitred end creating a venturi effect. An anti-backfire valve is attached to the outer end of the tube and a hose connects that to, in my case, the front tappet cover/oil seperator pipe that normally feeds the stock pcv assembly. A good vented oil filler cap or a quality aftermarket crankcase intake filter completes the setup. I really like this affair because I always have negative crankcase pressure and that helps keep seal leaks to a minimum and moisture out of my crankcase. With the engine running, a very noticeable suction can be felt at the end of the hose. It is also very clean looking with only a hose diappearing out of sight behind the bellhousing.

I found a stainless air injection pipe ('80's GM I think) in a junk yard that was threaded for, and had attached, the proper anti-backfire valve. Since I have a stainless exhaust, a little TIG welding fixed me right up. I did install a new valve and I used silicone hose in the area of the exhaust. I've seen carbon steel versions of the air injection pipes as well. The person who told me about this has had his JB Welded in his exhaust for six or seven years with no problem. And no, this does not suck oil out of the crankcase. Hope that I made some sense.
David
David

Never heard of that either David. Apparently several solutions for crankcase venting.
Greg Bowman

I like this idea! Since I've got a DCOE, my present setup is to route the breather hose to the air filter - and I've never felt that it created as much vacuum as it should. Time to get out the drill and the JB Weld!!!
J.G. Reed

The 69 model year should have the positive ventilation system comprising the carbs with the breather ports connected to a Y-piece connected to the front tappet cover, and a ventilated oil filler cap. Before that the PCV valve was used, also a positive system, before that the non-positive system with a pipe from the rocker cover to the front air filter can and an open pipe on the front tappet cover. The PCV is more trouble than it is worth, go for one of the other two. I also have noticed slightly higher oil consumption at speed (later positive system), but that is sustained 70+mph for a couple of hundred miles or more, but it isn't significantly higher. If you have oil gunking up the carbs then you have a serious engine problem, which will be pumping oil elsewhere if not via the carbs.
Paul Hunt

It was said 'I have noticed that after a sustained high speed running that my oil consumption increased noticeably.' Usually that indicates that oil is blowing out the seals, especially the rear seal, because of elevated pressures inside the engine. A friend built a vintage race car and I was crewing on its maiden voyage. He blew out a tremendous amount of oil each race from the rear seal. We couldn't figure it out. After the weekend was over I thought about it and realized his breather was way too small and created high pumping pressures. After modifying his 'catch can' his oil consumption problems ceased immediately.
MaGee

Went for another high speed run yesterday and had no oil in the PCV valve, so I guess my suspicions were correct.
Greg Bowman

David

You have my curiosity aroused, especially with the line about reducing oil loss through the "seals". What is the chance of a picture or two and a couple of sketches?

Thanks

Larry
Larry Hallanger

I'll jack my car up and snap a picture or two and send them to you as well as send a pencil diagram. I'm at about a first grade level in artistic ability, so don't laugh at my sketch. David Vizzards book on tuning A-series engines has a diagram as well. With no crankcase pressure it's easier for the oil to stay inboard of the crank seals or slingers.
David
David

Larry,
Did you get the pictures I sent?
David
David

Doug Jackson at his web site offers side covers that are less susceptible to oil flooding the ventilation system. Take a look at www.mgbmga.com.
Barry
Barry Parkinson

David

Yes, and Thank You! I was involved in non-MG things this past weekend and didn't have time to do more than just scan my email at home.

Larry
Larry Hallanger

One thing we might want to consider is how this oil mist injected into the exhaust stream affects NOX and other pollutant levels?

The real reason I bring this up is that many of us have to meet Smog testing requirements in our states, and sometimes that is hard enough to do (depending on the local rules) with a fully functioning OE smog setup or even just a PCV valve setup.

Introducing raw oil mist and other crankcase contaminants into the exhaust stream might just cause a car to fail, I think, and therefore, for those of us who want to ensure that we can continue to drive the cars on the road, a little more info on this aspect of the Evacupan setup. If my suppositions are wrong, then it would be instructive to know why and how this system would be able to cope with maintaining low pollution levels. A catalyitic converter might generate high enough heat to burn off the oil, etc, but I am not sure that the exhaust stream below the collector in a conventional setup gets that hot or what it might produce.
Bob Muenchausen

I did a search on ask Jeeves and found this.

http://www.team.net/html_arc/datsun-roadsters/200006/msg00551.html
Mark
MLS Somers

MLS: Marc Sayers is also noted for his insights into MGBs and their tuning.

One thing that I found interesting in his comments your link goes to (above) was his comment that this Evacupan system was for "race cars only". No explanation why, but it does make me wonder why he would say that.

Also, I am not sure how one relieves pressure by creating a vacuum and does not also simultaneously pull molecules of oil or anything else dispersed in the crankcase's atmosphere in the direction of the vacuum????? Traps will catch a lot of the big condensed stuff, but I am not sure the gaseous stuff doesn't find its way into the exhaust stream.
Bob Muenchausen

"it does make me wonder why he would say that" Complexity? Cost? One-way valves and all. Positive crankcase ventilation (PCV valve or not) *does* pull oil molecules from the crankcase but via an oil separator and flame trap that returns most of it to the sump. Although there is a partial vacuum, there isn't much flow due to the restriction of the oil filler cap (non-emissions cars) or the restrictor on the back of the rocker cover of emissions cars. I would expect a high flow to return a lot less to the sump and burn more. However at least one person here or on the mailing list had severe oil burning via the breather - he could see it pumping up the pipe when disconnected from the carbs - that was only cured by replacing the front tappet chest cover. In theory, unless you do have blow-by, there shouldn't be any pressure in the crankcase becase as two pistons come down the other two go up. But there will always be a little blow-by, and I have heard (but never understood) that piston movement is asymetric. The carbs put quite a lot of suck on the crankcase, so even through the flow is small (high flow would upset mixture), there is always negative pressure 'absorbing' any tendency to pressurisation. This can be felt and heard at the the oil filler orifice as a change in idle speed as the cap is removed and negative pressure if covered by the palm of one's hand. No idea of MJS's status, but I would only expect exhaust gases to create a venturi and partial vacuum if the breather pipe were very close to the open end of the pipe, like an aerosol. If it were before any silencer/muffler boxes, or too near the engine, I would expect back-pressure to nullify any suction. Either that or the breather pipe being connected to a part of the pipe that rapidly increased in diameter.
Paul Hunt

"One thing that I found interesting in his comments your link goes to (above) was his comment that this Evacupan system was for "race cars only". No explanation why, but it does make me wonder why he would say that."


Bob,
I believe he answered your question in the following paragraph, although at least in my limited experience, his statement is not true. I have a big bore stainless Falcon sytem on my car and it works just fine.

"Obviously this only works with
a low pressure exhaust (generally only an open exhaust will work though
I did build a system for a 510 race car once which used a big Flowmaster
muffler and the exhaust pressure was still low enough for the Evacupan
system to work) and this means race cars only."


Paul,
My simple little set-up works fine with suction from idle on up, hence no back pressure problems. As far as complexity and cost, an air pump valve is less than $20.00, the pipe is a scrap yard piece and the hose cost $3.00. It can't get much simpler or cheaper or work much better for my old B.
David

I would assume that the "racing only" disclaimer is similar to that on the lead substitute bottles that read "for off road use only" to keep from running afoul of environmental protection laws and emmissions control issues.
R. L Carleen

David,
it makes more sense now than when I first read it. Apparently, a low pressure exhaust is required to allow the venturi effect to overwhelm it where the tubing enters beyond the collector pipe.

R.L.,
That was my assumption too. And if so, then that may verify my concerns for people doing this on "street" cars, especially those in areas with stringent smog laws. Probably ought to write Marc Sayer for a better explanation.
Bob Muenchausen

I was envolved in David's car a bit and I was very impressed with the results. A much better and simpler system then any other I have seen. I plan to use it on my crossflow if it ever finds it's way into a car. The suction even at idle was amazing. Bob
Bob Thompson

This thread was discussed between 06/08/2003 and 22/08/2003

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