The Stovebolt Site Forums The Shop Area Engine Shop crankcase evac! this is diving me nuts

hey guys,
getting to the end of my 1958 235 rebuild and i'm a little confused about the crankcase evac system on these motors. I know the original method was with a "draft tube" but a pvc system would be more efficient. right?
The machine shop put a plug in the hole where the draft tube typically goes...and i know this motor had a plug in there before i tore it apart. this brings me to the conclusion that the evac system was primarily in the valve cover and air filter..nothing to the crankcase directly. WHAT SHOULD I DO?! I just want to setup a evac system that works nicely and discard the draft tube altogether.

there's info on the road draft and the optional PCV systems in the shop manual here

Bill

Some engines had a valve cover that vents on the top at both front and rear of cover, some had solid covers. I had a solid cover on my 235 and my 261. My answer to the pvc situation was to get a oil cap that had a pvc connection on it, then ran a hose to the intake manifold just below the carb. Been that way for years and no problems. Yes the draft tube was removed and a freeze plug inserted in it's place.

I just installed a PCV in my 1955 235. I turned an aluminum plug to plug the down draft hole and made it able to accept a PCV grommet from a mid 70s GMC van. As long as you have the baffle/shield in the block where the tube went you shouldn't have any problems. I ran the same PCV for the mid 70s van and ran the hose around the back of the engine to a fitting in the intake. Haven't had any problems so far and it seems to work great.

If you install a PCV system, you need a place to draw the fresh air in and another for the PCV. I converted my draft tube to the PCV connection and I installed a filtered oil cap on the valve cover. The idea is to move fresh air into the crankcase to replace the air laden with fumes. the system removes the water vapor too.

thanks for the input guys, is there a specific aftermarket PCV system anyone recommends for the 235? I'm still confused how the evac system was setup before I did the overhaul, I didn't find any PCV valve, or draft tube. valve cover has filtered oil breather and a tube that connects to the stock air cleaner (which im discarding) but i don't recall anything connecting to the crankcase itself. if there was would it be near the draft tube plug or somewhere else on the block?

Hook a hose to it and find a filter to put on it. You can let it sit in a tin can under the hood. All it needs is to be filtered whether it is through the air cleaner, valve covers filtered oil breather, or on it's own filter.

to purge the crankcase you dont have to have anything connected to the crankcase proper as the fumes can be evacuated out through the valve cover. The oil drain holes in the head provide a passageway for the fumes to be pulled from the crankcase by vacuum. Perhaps the fumes were drawn only by the slight vacuum at the carb airhorn. The pcv systems for 235s had to have been a Calif. only thing as pcv for the rest of the nation did'nt come out until the '63 cars. (no more 235s by then)

http://www.1954advance-design.com/Documents/EngineeringFeatures/slides/orig_Page61.html

http://www.1954advance-design.com/Documents/EngineeringFeatures/slides/orig_Page58.html

above link is for a 261, shows how the system flows.

A PCV system was available on some domestic GM small truck 6 cylinder engines as early as 1948. It was available as an option on all 1954 truck engines. It was not, however, standard on all trucks until much later.

I had a problem in a 71 nova 250 pulling to much vacuum thru the PCV and stumbling at idle. Solved by installing a vacuum actuated fuel petcock for a moped inline and operating it off the same hose as the vacuum advance. Worked great.

is removing the oil-bath air cleaner that connects to the top of the valve cover (putting breather on valve cover instead) going to effect the air flow? then all i have it a hose with a PCV filter in it going from the intake manifold to the valve cover.

a hose from the intake to the valve cover is an undesireable duplication of the one from the air cleaner to the valve cover .... having full engine vacuum to the valve cover is effectively a giant vacuum leak, and it's not going to scavenge the fumes from the crankcase .... you should really read the shop manual link I gave above carefully and understand how the system works .... the one hose you should leave is the one from the valve cover to the air cleaner - along with the vented oil filler cap, that will collect any fumes from the top end, you still need a proper venting of the crankcase

Bill

did'nt know that -was refering to standard production stuff.
Have you ever personally seen one of those optional jobbies? I would think they were a little sold option ('cept maybe in Calif.)

the crankcase is common (by way of oil drain holes and 12 pushrod holes)with the valve cover and the side plate, so picking up fumes at any of these places is sufficiently adequate and takes care of the entire engine. Whichever is most convenient or adaptable to use.

so im clear? the book doesn't give a good description of where the PVC lines connect on the engine. How would YOU guys hook up your crankcase evac? pics?

rig it like any of the post '62 inline chevys. For a 235 with say a '55 nonvented valve cover use the filtered oil fill cap for fresh filtered air intake and suck it out of the valve cover (maybe a welded-on 3/4" nipple and hose with a pcv valve plumbed to the intake manifold. make sure the pcv valve allows flow toward the intake-they make them to flow both ways-pay attention to any flow arrows. The system will make most any older fumer fumeless, and the cab atomosphere more pleasant on hot days.

In 1954, the PCV system was plumbed like this .

Here are pictures of the original parts both on and off the truck for your reference. Truck was a 1954 6400 farm truck.

http://www.flickr.com/photos/advance-design_parts_co/8129417263/in/set-72157631868452754

You want to draw the fresh air through the motor. If you use a fitered oil cap for the intake then you should connect the PCV hose to the crankcase.

Brad,

Is that a disconnected hose from the air cleaner between the valve cover and the rear of the carburetor?

That hose probably comes from the rear driver's side of the valve cover and should be connected to the tube-fitting on the top of the air cleaner?

your link didn't work tclenderman. truckernix thanks for the clear input, There's a couple bolt holes that open right into the crankcase where an oil filter can adapt to (mine 235 was ordered without one), should i just run a hose from one of these holes into my intake? and then a breather on the valve cover.

Yes it was disconnected in the photo Tim. It came off the valve cover to the air cleaner. Tim your link works for me.

You most likely have the remains a AC Spark Plug retrofit kit. The state of California required a closed PCV retrofit on all light vehicles from 1950 through 1960. Starting in 1961 all California cars and light trucks were factory equipped with closed PCV system by law.

An AC Spark Plug retrofit kit consisted of freeze plug to seal the crankcase after the draft tube was removed. Hose barbs and a hose were installed from the air cleaner to valve cover (provides clean air to the engine). The vented oil cap was removed a replaced with sealed oil cap. Another hose barb was installed in the side of valve cover towards the front of the engine. A quarter inch hose was attached to the barb, the other end of the hose is where PVC valve was installed. The other end PCV valve connects to 3/8" hose. This hose was then connected to brass block installed on the intake manifold.

The AC part numbers were CV3 for PCV valve kit. The state of California required the system be closed, so another kit (KV1002) was required to seal up the engine, it contained a sealed oil cap, freeze plug for road draft tube, and a hose kit from the air cleaner to the engine.

The PCV valve in the CV3 kit was CV609. Is this the "filter" you are talking about? CV609 valves are easy to find on Ebay.

It rare to find a complete kit on these engines, most were "modified" somewhere down the line. Most people did not understand system and removed/modified it.

darn, you really know your crankcase evacs! haha you described my setup perfectly piece for piece. I would just hook up the same exact system but i have a couple of variables that don't allow that.
1) new air cleaner that doesnt connect to the valve cover
solution: K&N breather on valve cover?
2) new offenhouser dual carb intake manifold, which doesnt provide a large enough pipe thread for the brass piece
solution: use smaller hose fitting that is provided on the intake and connect that to a new AC spark plug and then into the side of the valve cover.

will this work?

Installing a K&N breather on the back hose barb will be OK.

A good hardware or plumbing supply house should be able to set you up with a 3/8 hose barb for your manifold.