Crankcase Ventilation System

[Bob Bidonde]

I would like to see pictures of crankcase ventilation systems in use on Model A and Model B engines.

Once upon a time I had a simple crankcase ventilation system on my Model B engine that kept smelly crankcase gases from blowing into the car at highway speeds. The system consisted of a cap on the breather pipe with a hose that routed the crankcase gases to carburetor. At speed, the low pressure at the air intake throat of the carburetor drew crankcase gases into the air-fuel mixture. The GAV made it possible to tune the air-fuel mixture.

I will be re-installing a crankcase ventilation system again, and I would like to see how others have done this. This time I a thinking about a closed and positive system that routes the crankcase gases into the air-fuel mixture like used on cars in the mid-1960s.

[H. L. Chauvin]

One I saw was perhaps similar to the one you mentioned. I saw it as early as about 1949 & it was installed by my mechanic/inventor uncle in 1932 in his boat with a B engine.

The removable oil filler cap was neatly modified with soldered sheet metal to "completely" seal the cap at the upper end of the oil filler tube.

A "completely" sealed 3/4" copper tube was solder connected to the front of the oil filler tube, routed around the front of the engine above the timing cover, & again "completely" sealed & connected to the Model B Air Maze device clamped to the intake of the Model B carburetor.

This 45 degree Model B Air Maze device had a flame arrestor mounted to the pot metal Air Maze device. (Model A has a 90 degree Air Maze device.)

As soon as the engine started, the suction at the carburetor intake immediately began to withdraw all of the fumes from the oil pan.

(Caution: One tiny pin hole in this suction tube, connections, or oil filler cap will severally decrease carburetor intake suction operation. E.g. to witness this malfunctioning event, just place one tiny pin hole in a straw & try to draw Coca-Cola out of a glass or bottle with a leaking straw ......... same effect with a pin hole in the side of a cigarette ...... old trick to see almost "NO" smoke withdrawn).

One can imagine in an inboard engine type of boat, with engine up front, & passengers seated in the rear, traveling at 45 mph with no firewall, inhaling oil pan breather fumes being pushed to the rear can become most annoying in a short period of time.

Higgins copied lots of other marine engine modification features & lofting design from this boat when developing his WWII PT boats.

Hope this information helps.

[Terry, NJ]

Al marine engines used a spark arrester type air cleaner with a pipe (or some other arrangement) that directed the fumes back into the engine. Fumes in a boat hull are a big deal! Gas and other fumes can lead to an explosion and there's no place to go so they gather. This is the purpose of the fore and aft scuppers and the stovepipe that directs the air to bottom of the hull (Fore) and up and out (aft). They are not there just to look nice, although they do.
Terry

[Jim Brierley]

Look in my book, page 142. It is on an OHV engine but applies to flatheads too.














look in my book

[CarlG]

Originally Posted by H. L. Chauvin

...
(Caution: One tiny pin hole in this suction tube, connections, or oil filler cap will severally decrease carburetor intake suction operation. E.g. to witness this malfunctioning event, just place one tiny pin hole in a straw & try to draw Coca-Cola out of a glass or bottle with a leaking straw ......... same effect with a pin hole in the side of a cigarette ...... old trick to see almost "NO" smoke withdrawn)...

In High School, I dated a girl whose mother was a heavy smoker. I didn't win any "brownie points" when I did this to a pack of her cigarettes.

[H. L. Chauvin]

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Hi Carl,

This was often times a very often used high school trick to offer a new young smoker a smoke & watch their cheeks sink in tightly against their teeth trying to draw smoke. LOL

[MikeK]

Read This:

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[CarlG]

Originally Posted by MikeK

Read This:

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Looks pretty clear to me.

[H. L. Chauvin]

Bob,

In simple laymen's term, the tube from the oil filler tube to the air maze connection at the throat of the carburetor that you & I both experienced before will work just fine to capture engine fumes in a car or boat.

Again in laymen's terms, smelly fumes from blow-by are allowed to exit the engine because the pressure "inside" the engine is greater than lower atmospheric pressure "outside" the engine; hence, smelly fumes are just gently pushed to the outside.

You only need to provide a very small amount of vacuum to capture these "low" pressured fumes exiting the engine ............ now if you want to get bold, just create a suction with a vacuum pump strong enough, & you can suck all of the oil out of the oil pan ...... better yet, increase vacuum more & you can make the thin metal oil pan collapse ....... just apply a little common sense.

Do not connect this sort of suction tube to the intake manifold where pressure is greater at idle & decreases greatly when the throttle plate is opened ........ again with laymen's terms, remember old vacuum wipers where when one pressed on the gas to pass a car & the vacuum drops so low the vacuum windshield wiper stops working.

With or without a flame arrestor, or with a properly sized "large" K&N Hi-Boy air filter, with a tube connection at the Air Maze device at the throat throat of the carburetor, there can never be enough vacuum to suck the oil out of your engine or make the oil pan collapse, or make your clutch plate touch the crankshaft pulley up front.

Remember at the preferred increased highway speeds you mentioned above, there will be more vacuum on the out-side of the throttle plate & less vacuum on the engine side of the throttle plate in the intake manifold ...... at idle, these two same vacuum readings will reverse & read just the opposite.

Hope this helps if blow-by is a problem -- some cannot tolerate smelly fumes because of migraine headaches & other causes.

[Bob Bidonde]

Thanks all for your replies.

[H. L. Chauvin]

Bob,

Also allow the tube from the oil filler tube to enter the Air Maze device at 90 degrees to create a venturi effect on this tube in this partial vacuum, at the out-side of the carburetor intake.

Without getting into the private lives of Giovanni Venturi, or Daniel Bernouilli, with their p's, u's, & v square equations, (again in laymen's terms), just think of the operation of an old simple "Flit Gun" which can still be observed on Ebay now & then.

Also remember one tiny pin hole in the "Flit Gun" can below, like with the cigarette smoke, the "Flit Gun" ceases to operate.

[Jim Brierley]

For what it's worth, PCV valves are designed to use a small orifice at idle (high vacuum) and a large one at opened throttle (lower vacuum). Those used on trucks years ago could be easily disassembled for cleaning.

[Chris in CT]

Hi Bob,

I chose a slightly different approach from the oil filler tube modification cited above, but very similar to the marine "flame arrestor" also referred to. I drilled and tapped a 1/2-20 hole into the valve galley cover, at the top of the cover. I made a small baffled fitting to screw into the hole, and connected it via rubber tubing to the intake of my air maze attachment.

I feel that it is more effective than the oil filler tube attachment because it allows the crankcase to breathe directly, and completely eliminates the oil percolation through the filler tube that so often happens with the Model A engine at higher engine speeds. In addition, it is barely visible and you would have to be observant to even see it. The engine runs noticeably cooler, and the engine bay is as clean as a whistle.

Sorry for no pictures, but I still haven't figured out how to post these yet. Happy Motoring!

[David L. Holloway]

How much crankcase oil dripping from filler tube cap while engine running is normal? My 'A' engine was rebuilt 40 years ago but very few miles driven since. Just now completing restoration.

[glenn in camino]

If your rings are seated and your engine is tuned properly, You shouldn't need any special ventilation. Model As run pretty clean.

[Bikerider58]

Like many I get a bit of oil mist on the engine from the filler, no worries, but it Air is blown out then air with dust and grit is sucked in.

I have one of the spring cap things with a side vent, so I plan to add a small cone air filter. Not too small, something from a dirt bike intake. This should allow no grater air flow resistance than the current cap and block the sand.

[Mike V. Florida]

I seem to have lost the rest of the details don't know if this will help,

[redmodelt]

Back in the Model T era there was a unit that could be installed in the Model T oil fill hole and allowed fumes from the crankcase to be pulled into the carburetor. This was made for use in cars not boats but is in principal the same thing. I made one for my Model T, while not as sealed as units described above, it helped some.

[duke36]

The attached was from our parts bin, circa 1970. PCV valve inside hose, one end to valve chamber cover, other to intake manifold with wiper tube connected at threaded fitting.
Not sure who "designed" this, but recollection was from some club newsletter.
I remember it was tried and removed because of tuning issues. Now we use the larger '32 oil breather pipes with a lightly screened, (no copper mesh!) stock cap.

[Joop]

Shown a new set never used (Yes it is for sale at Swap site)

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