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CJ-3B Bulletin Board

Welcome to the CJ-3B Bulletin Board, the forum of CJ3B.info. Everyone is invited to view the postings here, but you must register as a member in order to post messages. The moderator reserves the right to remove items posted. Items may be archived on the Tech Tips page. If you post a problem, please follow up by posting the solution when it is found, as it will likely be useful to other readers. For forums covering other Jeep models, see the bottom of this page.

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Pages: (2) 1 [2]  ( Go to first unread post )

 PCV vent tube. sucking air in?
Rus Curtis
Posted: Apr 27 2012, 07:40 AM


Group: Members
Posts: 1,287
Member No.: 11
Joined: 16-October 08

Good luck with your project! You can spend a lot of time on the 3B Page looking at all the images and reading the articles, but it pays off as there's a lot of info here! I've spent hours upon hours looking and comparing different angles, different years not to mention different approaches to modifications. Very educational!

Rus Curtis
'54 CJ-3B
Bantam T3-C
Posted: Apr 28 2012, 03:35 PM


Group: Co-Admin
Posts: 5,374
Member No.: 3
Joined: 12-July 08


Know that every internal combustion engine must be ventilated.
The internal combustion engine is basically a pressure and a vacuum pump.
When a cylinder fires, a small amount of gas pressure called blowby seeps past the piston rings and valve guides.
If unvented a sealed engine will blow out the weakest gasket in order to reach atmospheric pressure.
Prior to crankcase ventilation it was considered as normal for all engines to exude oily sludge deposits.
For this reason 2 basic types of engine crankcase ventilation have been developed.
There are open crankcase ventilation systems and closed crankcase ventilation systems.

Willys Motors is generally credited with developing the closed crankcase ventilation system.
From its inception the WWII military LRV mandated a closed ventilating system.
At that time this closed system was not considered as being advantageous beyond promoting deep water fording capability.
In fact the civilian SW and PU models with L-134 Go-Devil engines from 1947-1950 used simple open crankcase system.
The Go-Devil powered DJ-3A also used the open system from 1956 onward.

The Hurricane engine began replacing the Go-Devil engine as early as 1950.
The Hurricane engine itself has perhaps the longest production history of all automotive engines.
It was produced virtually unchanged from 1950 through 1971.
Initially both types of systems were also used on the Hurricane engines.
The open system was originally installed on the SW, PU, DJ and industrial engines.
The closed system was always installed on the MA, MB, MC, MD, CJ and FC engines.
Over the years 4 different crankcase ventilation systems were installed on the Hurricane.
1 being the open system and 3 being closed ventilation systems.
The specific intake valve cover installed should best determine what system was used for any particular Hurricane engine.


Open crankcase ventilation consists of a breather and a ventilator.
The breather for a Hurricane is located on top of the intake valve cover.
This breather cap can also function as an oil fill, albeit without the oil level indicator.
It has an integral mesh filtration / restriction built inside of the cap.
This mesh restriction is two fold in function.
It restricts pressure outflow and filters any incoming airflow.
It really makes little difference from where a crankcase vents pressure out.
When not in motion pressure can and does exit the breather cap.
When pressure ocassionally tries to escape via the breather, an oil film forms on the breather mesh.
The oil film further restricts outflow and also helps clean the inflow air of dust particulate.

The mesh cap fibers restrict the pressure from escape and that promotes pressure escape at the unrestricted ventilator.
The ventilator commonly called a draft tube is a straight tube out from the exhaust valve spring cover.
While in motion outflow occurs when air passes by the tube opening, thus creating low pressure at the ventilator port.

By 1958 50% of all smog was credited to fumes from the open crankcase ventilation system.
It was also realized that burning of the crankcase fumes leads to a much cleaner engine inside.
In 1961 all Willys engines went to the closed ventilating systems.


With all closed systems the Hurricane must have increased air intake because the crankcase is literally sucked clean via the intake manifold vacuum.
This increased air inflow first passes through the Donaldson air filter.
From there it is plumbed directly into the oil filler tube providing direct access to the crankcase.

On the 1st closed Hurricane system (1952 - 195?) a "tee" fitting was inserted just before air inflow enters the oil filler tube.
This routes a portion of the filtered air into the intake valve cover by way of a special dome cover.
With this system the air inflow is actually redundant because it enters the crankcase at 2 locations.
Evidently the concept was to better sweep bypass fumes from the upper valve cover.

On the 2nd closed Hurricane system (1955-1965) there was no "tee" fitting to divert a portion of the inflow into the intake valve cover.
This particular valve cover has no provision for any plumbing attachments.
This system was always used on FC's to reduce the engine height.

These 2 earliest closed systems both retain the exact same PCV valve that was developed for the Go-Devil.
This particular PCV valve is likely the finest PCV valve that's ever been designed.
It is easily cleaned and most of the original valves in service are still operating todate.
Excepting the integral by-pass port the valve is pulled closed during engine idling.
When the manifold vacuum drops during acceleration or under load
the valve opens fully to allow more bypass gasses into the intake manifold.
It is very simple and highly effective !

Both of these 2 early closed systems use a combination AC fuel / vacuum pump.
The lower vacuum pump portion of the AC unit was tied into the PCV system.
The vacuum hose was connected to the Trico vacuum wipers.
With the Trico wipers in use, output air from the AC pump went into the intake manifold tubing.
With the Trico wipers inoperative no airflow exits the AC air pump.
The wiper airflow or lack thereof has virtually no effect upon the manifolds intake.
Therefore the dual AC fuel / vacuum pump is not required if one does not have vacuum wiper motors.

On the 3rd closed Hurricane system (1966-1971) the fuel vac pump was eliminated and replaced with a fuel pump only.
As before the inflow air was filtered by the Donaldson before going straight into the oil filler tube.
Pressure outflow was relocated away from the exhaust valve spring cover.
Pressure outflow was by way of the intake valve cover with yet another dome design.
Pressure outflow is routed directly into the manifold port using a later PCV valve design.
This late PCV valve is not as easy to clean nor as durable as the original PCV design.

It is my observation that the open ventilation system allows the most internal sludge to accumulate.
The other 3 closed systems are relatively negligable concerning sludge buildup.
I generally prefer the 2nd closed system because it uses the better quality PCV valve and reduces valve cover height.


The closed systems may be tested for correct operation.
First determine if the oil fill indicator cap has a good gasket seal.
Remove the filtered air intake hose from the oil fill tube.
Warm engine and operate at idle (550) RPM.
Attach a vacuum gauge to the sealed oil filler tube.
Reading of the gauge should reach 3 to 5 inches within 10 seconds.
A low or zero reading indicates a clogged valve or air leaks in the system.

Currently rebuilding RANGER ... 1962 CJ-3B / Hurricane F-134 / T90C / 5.38 / Powr Lok Front and Rear / Deluxe Koenig Half cab
St Louis Area
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