The 36 had Positive Crankcase Ventilation but not the "closed" type we see today. To convert to the closed system would take a lot of work but could most certainly be done. Tony
Good morning Tony. Crankcase ventilation on my '36 engine consists of air entering the engine through 3 small louvers in the valve cover and exiting through a draft tube connected to the oil filler tube on the left side of the engine block.
It is interesting how driveability issues like this create different levels of interest on different forums, probably reflecting whether the old vehicles are primarily driven or displayed. Here's the response this inquiry got on the stovebolt forum:
So there is actually quite a bit of specific information on how to select the proper PCV valve that creates the correct crankcase vacuum (1"-3") and how to install a PCV system on an old inline 6. The intended benefits are keeping the engine insides cleaner and reducing seepage of the primitive front and rear crankshaft seals. I'm going to make my PCV as "stealth" as possible like the 3.55 rear gear conversion and tandem master cylinder on my '36. One will have to look carefully to find the PCV valve attachment at the oil fill/draft tube and at the intake manifold windshield wiper vacuum port to notice it.
It seems that "display 'em" use of the antique vehicles may be more prevalent in urban areas and "drive 'em" use may be more prevalent in rural areas.
In your case part of the process of "closed" system would include closing the valve cover louvers, connecting the road draft tube between the air filter and carburettor and then fitting a PCV valve between to valve cover and the intake manifold after the carb. Also making sure there are no other air leaks into the crankcase. Tony
"In your case part of the process of "closed" system would include closing the valve cover louvers, connecting the road draft tube between the air filter and carburettor and then fitting a PCV valve between to valve cover and the intake manifold after the carb. Also making sure there are no other air leaks into the crankcase."
Good morning Tony.
Thank you for your interest in this project. I've gotten responses from a couple of people who have added PCV systems to older Chevys and they attached the PCV valve between the draft tube and intake manifold. If I use that air routing I was thinking of trying to mount some air filter medium on the inside of the valve cover at each of the louvers to make the PCV conversion more "stealth"
Your '38 looks really nice and reminds me of what my '36 looked like back in the early 1970s when I was restoring it at home. The restoration still looks quite presentable and my wife and I drive it a couple of times a month.
There is a guy in your part of the world, or maybe in New Zealand, who makes direct replacement halogen headlight bulbs for the 1930's era vehicles. My OEM '36 generator with a James Paterson voltage regulator hidden inside powers those much brighter halogen bulbs no sweat, despite "expert" assertions that the old generators can't keep up with halogen bulbs ("Globes" down under, right?), .
I didnot intend to say my idea was the only way to do what you wanted to do only to point out that there was a reasonable amount of work involved, there are several routing choices available and your ability will be the deciding factor. I am half thinking of doing a version on my 38 but as I dont need to pass a smog test probably wont go to the trouble.
As for my my 38 I bought it 40 years ago and still havent driven it under its own power yet though that is getting closer by the year but so is retirement. I am not sure that it will stay that colour, I think to much red and not enough black for 1938 but there is time to change it as that is only a sealing coat of color.
I did see a posting about the halogen light replacements but havent made a decision in that regards yet and also about the Paterson regulator though I may well have difficulty tracking both down now though there is no rush at this stage. You are right about the "globes" bit , "bulbs" grow in the garden. Tony
"there are several routing choices available and your ability will be the deciding factor. I am half thinking of doing a version on my 38 but as I dont need to pass a smog test probably wont go to the trouble."
Good morning Tony.
Making a PCV system looks simple from the examples I've seen on various forums, especially if you're not trying to hide it from view. The simplest seems to be amputating the draft tube, welding a washer onto the stump that will accept a PCV valve grommet and valve and routing that to the existing windshield wiper port on the intake manifold. The part of the system that admits air into the engine should probably use filtered air, either from the air cleaner housing (an obvious, in your face modification) or a more stealthful mounting of filter medium on the inside of the valve cover at the louvers.
My motivation in doing this is to try to reduce the weepage of oil from the crude crankshaft seals that isn't really causing a problem but is messy. A slight vacuum of 2" or 3" in theory should help. We'll see. I assembled this engine in the early 1970s. If I were doing it today I'd put modern crankshaft seals in it. At age 73 pulling the front clip off the '36 pickup to access the timing cover seal has no appeal.
Brino I see your problem and agree with your routing idea as a workable 1. I am putting my 38 engine together now and can see the modern seal would be much better than the slinger that is there now and can see a couple of ways to change to either a "graphite rope" or a more modern "neoprene" type seal but I am going to risk it and use the slinger. Others have posted that the check ball in the rear main bearing cap often sticks allowing a leak especially if it sticks shut, clearing it does mean dropping the sump pan though. If the ball is stuck I am not sure the PCV system will cure the problem. Tony
One thing to keep in mind is that a PCV is a vacuum leak. If you look at almost any factory system, the PCV will be plumbed in such a way that the incoming air/vapor mixes with the air/fuel mixture coming from the idle jet and transfer ports in the carburetor. This almost always means a plate right under the carb with the discharge right under the idle jet, or something similar right in the carb casting. This is not an accident.
I have seen a few systems that just have PCV plumbed randomly on the manifold somewhere, like the wiper port, or power brake port or whatever. Some Ramblers were like this in the mid 60s when they were sold for California. I have seen a few others, but it escapes me right now what they were. Ir results in a miss on one or more cylinders, and the carburetor must be richened a lot to get all cylinders firing. Cars run lousy like this, and the emissions are off the scale.
If you do it, plan on plumbing it in under the idle jet. You might have to work on the mixture in the idle and transfer port area, but maybe just richening the idle screw will be enough to compensate for the PCV (sometimes it is).
There is a limit to how much air you can leak in this way without causing driveability issues, even if the mixture is correct. Usually you would pick a PCV valve for something of about the same displacement as what you have, but in this case I would go even smaller, due to the slower idle of a 1930s engine.
The biggest PCV valve you can get away with still wont be enough to ventilate the crankcase at all times. It is going to blow backward part of the time. If you have an open breather, like a breather cap, it will make a mess. In the 80s, they plumbed the PCV intake into the air filter. That made a mess all over the air filter element instead of the engine. I'm not sure what the effect would be on an oil bath air cleaner. Maybe nothing.
Either way, there just needs to be a way in (breather) and a way out (pcv valve). The more territory you cover the better. I suspect this is why you see them at opposite ends of the valve cover on newer Chevrolet sixes. The downside is it makes a mess on the valve cover.
"Others have posted that the check ball in the rear main bearing cap often sticks allowing a leak especially if it sticks shut, clearing it does mean dropping the sump pan though. If the ball is stuck I am not sure the PCV system will cure the problem."
Tony, do you know if a '36 has that check ball? I've made a temporary installation of the PVC system and found that there is a really big air leak at the rear main bearing that prevents a vacuum from forming in the crankcase with either manifold vacuum or with a vacuum pump that I use for air conditioning service. When slight pressure is applied to the crankcase the air leak is audible inside the bell housing. The next step is probably dropping the pan to check bearing clearances. Hopefully readjusting the bearing clearance will allow a vacuum to form. The engine has only 13,000 miles but I assembled it nearly 50 years ago and I don't remember the bearing clearances I got. The bearing work was done by Egge Machine in California and they do really low quality work. After boring the block they left it outside in the rain and the fresh bores rusted. Nice, huh?
"Either way, there just needs to be a way in (breather) and a way out (pcv valve)."
Bloo, thanks for your insights. The air will come in through 3 louvers in the valve cover. I will put filter medium over them. The PCV valve is inserted into a grommet in a 1 1/4" metal tube I welded to the side of the draft tube. The draft tube is very thin (1/32") but with my tig machine I was able to make the weld without any problem. Tig is a really effective welding process. With it a guy could weld a razor blade to an anvil. The bottom of the draft tube is plugged with a 1 3/16" freeze plug.
I'm hoping to eliminate the air leak with a correct bearing clearance of about 0.0015". A PCV valve that applies a low vacuum of about 1"-3" Hg will hopefully not draw air in through the rear main bearing as the valve cover louvers will hopefully be the "path of least resistance". What do you guys think?
I've swapped emails with Deve Krehbiel who makes PCV kits for vintage vehicles and he's never heard of one being put on a '36 Chevy so he doesn't comment on the possibility of curing the rear main leak.
"Devestechnet.com has some of that. I have no input on the subject."
Wisebri, I followed his example in doing my project, including getting the PCV valve he recommends.
After writing the above Pre 68 Dave on the Stovebolt forum pointed out to me that my air leak is not along the crankshaft - bearing interface. The air leak is through the oil drain back hole at the bottom of the slinger groove in the block and main cap. That hole allows the vacuum I try to create in the crankcase to draw air in through the drain back hole. That appears to be a fatal flaw in my intention to put PCV on a '36 Chevy engine.
If your primary intent is to reduce the bearing seal weeping/leakage, perhaps your best approach is to directly work on those areas. There are quite a few posts about all that can be done to minimize that. And it will not affect the drivability of the engine.
Using ideas and inputs from various members I was very successful in reducing rear seal leakage on my "37 to almost nothing.
I may be sort of shooting from the hip here, as we are talking about stuff I haven't thought about in a long time, but the 1-3" of vacuum in the crankcase does not ring true to me. I don't think there should be any vacuum in the crankcase in a perfect world, and in the real world only the residual vacuum that is unavoidable due to the filtering media in the inlet (breather cap or equivalent). I seem to remember that vacuum in the crankcase, such as you might get with a restricted breather cap results in oil burning. Your inability to pull a vacuum with a vacuum pump sounds completely normal to me.
If I remember correctly, the two things to pay attention to when selecting a PCV valve are flow, and the vacuum at which the valve opens. To get the flow right, you might have to just pick something from a similar displacement engine. The vacuum rating (which is in a book from one of the manufacturers, probably fram) has not to do with the vacuum in the crankcase, but how much vacuum it takes to open the valve. This matters if you have a big lumpy cam or something. For instance, if you only have 8" of vacuum at idle, the valve might never open, unless you pick one from some high performance Corvette that opens at 6" or whatever. For smooth idling applications, like a stock 207, there are probably many valves that would open at about the right vacuum level. The PCV valve only acts as an orifice in normal operation, and the only purpose of the valve function is to slam shut during a backfire and prevent a crankcase explosion.
The absolute limit is going to be how much air you can leak/mix with the idle air/fuel (CFM) and still get the carburetion to work properly. It is never enough air.
"I may be sort of shooting from the hip here, as we are talking about stuff I haven't thought about in a long time, but the 1-3" of vacuum in the crankcase does not ring true to me. I don't think there should be any vacuum in the crankcase in a perfect world, and in the real world only the residual vacuum that is unavoidable due to the filtering media in the inlet (breather cap or equivalent). I seem to remember that vacuum in the crankcase, such as you might get with a restricted breather cap results in oil burning. Your inability to pull a vacuum with a vacuum pump sounds completely normal to me."
The article is directed at the 216/235/261 Chevy engine.
"All Chevrolet engines through 1939 had the ball bearing check valve."
Gene
Thank you for that information. I assembled the engine I'm trying to retrofit with a PCV system in the early 1970s and because it's been so long and because my memory is very porous now I have no recollection of that check valve. I have seen it referenced but I have not seen a photo or diagram of it. Do you know of a photo or diagram?
If applying a vacuum to the crankcase would tend to pull that check valve open then this PCV project is probably a lost cause because with that check valve open the crankcase is open to atmospheric pressure and the vacuum would simply pull outside air in through the oil drain back hole. That would have the dual adverse effects of pulling unfiltered air into the crankcase contaminating the inside of the engine and eliminating the vacuum that is needed to pull blow by gases into the intake manifold to burn them in the combustion process.
If I were 30 years younger I would machine the back of the engine for a rear main seal but at age 73 that has no appeal. Pulling the engine, removing the crankshaft (probably the whole rotating assembly) then setting up a boring bar at the back of the engine to machine the block and rear main cap for a rope seal is more than I can take on anymore. I'll let my sons or grand kids tackle that project when this '36 belongs to them.
If anyone who is following this discussion has access to a '36 engine rear main cap I would really appreciate a photo showing that check valve. What I have to offer in exchange is photos of all the other parts of this PCV system that I have already made. That includes the oil fill/draft tube with the bottom of the draft tube plugged with a 1 3/16" freeze plug and a PCV valve inserted into the side of the draft tube, the grommet and PCV valve used, a 3/8" hard line to connect the PCV valve to the intake manifold windshield wiper vacuum port and the fittings used to make that connection.
I don't take my '36 pickup to shows because after winning Class T2 at the 1976 VCCA National Meet in Colorado Springs there's nothing left to prove and it's really much more fun to drive it than to show show it. But, like the other modifications from original I've made to it (3.55 rear gears, modern tie rod ends, tandem master cylinder, etc) the PCV was going to be a "stealth" modification that would be well hidden and barely noticeable. It would be nice if the PCV could actually be done. If anyone would like to collaborate by suggesting a way around that rear main cap oil drain back vacuum leak, please do. Any and all suggestions will be gratefully accepted.
I see no advantage of a PCV ststem for a car that is normally driven at speed, especially in temperatures above 60 degrees. It is great for a city car tha is driven short distances and with a lot of idling and speeds under 30 MPH. The air passing over the end of the road draft tube (breather pipe) will pull a higher capacity of air through the engine than a PCV system can.
"It is great for a city car tha is driven short distances and with a lot of idling and speeds under 30 MPH."
That's my '36 Gene. It's driven over to the park, 12 miles away, for a picnic a couple of times a month. That's why it's only accumulated about 13,000 miles since 1976.
What can you tell or show me about that oil drain-back check valve?
I stay interested in this '36 by doing projects like this. The last one was finding (a 40 year effort) and installing a factory fa shroud even though it has never had an overheating problem. How many of those fan shrouds did you sell?
Before the fan shroud the project was a "Stealth" tandem master cylinder that bolts to the original MC holes.
Before that it was 1950 Chevy car 3.55 rear gears in a 1937 Chevy car rear axle, another "Stealth" modification.
Brino The purpose of the ball valve at the rear main is to prevent rear main oil leak when parked on steep slope and the oil level rose above the crankshaft opening. Sometimes the ball will stick allowing/causing a leak depending on where it stuck. Tony
Thank you all for your interest and suggestions. I think that updating the '36 engine with a PCV system would only be possible if the block and rear main cap were machined for a rear main seal. The reason is that the oil drain back hole in the rear main cap is open to atmospheric pressure and acts as a massive air leak that prevents pulling a vacuum in the crankcase. Applying a vacuum to the crankcase would have the effect of pulling unfiltered air, including road dirt and clutch wear dust, into the crankcase through the drain back hole and the rear main bearing clearance.
Whatever might be gained by vacuuming water vapor and other combustion byproducts out of the crankcase would probably be more than offset by the contaminants that would be sucked in.
It seemed like a good idea based on the Deves article but is a lot more complicated than I first imagined on the '36 engine.
If I were rebuilding the engine today, instead of about 45 years ago as actually happened, I would add a rear main seal. I would also adapt in a modern clutch pressure plate to get a smooth clutch engagement instead of the hair trigger clutch engagement of the 1930s. My 1971 Dodge van, that I bought new and still have, has a truly silky smooth, totally progressive clutch engagement that I wish my '36 had. I can stop the van on a steep uphill then continue up the hill as smoothly as if it had an automatic transmission. Oh well, people in hell want ice water too.
You have to remember that the engineering going on at Chevrolet during 1936 produced a very dependable truck for the road conditions of that time. Chevrolet improved the engine of 1935 in '36, from the one in 1934,33. It went on with more improvements in 1937, etc. Also, you have to remember the general public's reluctance to accept new ideas about auto making. The stock market that every person in the 1920's owned stock in had crashed and that "new idea" of owning stock broke so many well intended persons. "New ideas" were not well accepted. The ideas of hydraulic breaks, steel bodied doors and door post, safety plated glass, steel top roof and many other so called improvements had to be "proved by the general public before being accepted as good". I well remember my Grandfather saying cylinders in engines should always be standing up because if at a slant the rings will wear out on one side and it will burn all the oil in the country. Those beliefs had to be changed and it took generations to do it. Engineering advanced ahead of acceptance and still does.
"Those beliefs had to be changed and it took generations to do it. Engineering advanced ahead of acceptance and still does."
Terrill,
You are so right on that. One who really resisted was Henry Ford. His engineering staff had a really hard time dragging him forward. He resisted hydraulic brakes until 1939 although Chrysler had them in 1926 and others may have had them before that. Henry also resisted overhead valves until 1954.
In the auto industry it's the bean counters against the engineers. Examples are the Pinto gas tank explosions and the Corvairs that would flip while cornering. And the same thing continues to this day with the exploding air bags.
One thing I have to give Ford credit for is they did not have to beg for corporate welfare in 2008 the way GM and Chrysler did.
Thank you very much for that photo. I wonder if you would be willing to send it to me as an attachment to an email so I could really zoom in on the rear main cap. I haven’t totally thought this through yet but it seems that if a steel tube like an oil pump pick up tube were inserted into the drain back hole and extended down below the upper level of the oil in the crankcase, then applying a vacuum to the air volume in the crankcase would not pull a large volume of air through the rear main cap area. To work properly the PCV system should inhale through the valve cover and exhale through the PCV valve that I have adapted into the side of the draft tube.
PCV conversions are actually pretty common on later year Chevy and GMC vehicles from what I see on the Stovebolt forum. It would be nice to figure out how to do it on 1930s era vehicles. If you’re a do-it-yourselfer like me you may be curious to see where this may lead. Others may be interested also. What do you think guys?
