The Stovebolt Site Forums The Shop Area Engine Shop Out with the Draft tube

I have several questions about the draft tube. 1949 216 3600

Is it hollow or is there a screen or filter in it?

Should it drip oil over night after a 15- 20 mile drive? Just a nickel size drop.

Can I remove it and plug the hole and install a pcv valve in my valve cover?

Or must I install the valve in the hole like Deve does it?

Is it considered a modification away from “stock original” if I remove the draft tube and go with the pcv valve?

I would like to see more options than the Deve method. But it is a good one. It just seems backwards of other cars.

Thanks Don

Air goes into the valve cover through a vented fill cap or a line plumbed into the "clean" side of the air filter element, and out of the modified crankcase vent standpipe with a PCV valve installed instead of a draft tube. DO NOT eliminate the standpipe and install some sort of Mickey Mouse plug with a PCV installed into it- - - -you'll end up using massive amounts of oil. There absolutely must be a positive flow of air through the engine, not a single line with a PCV in it.
Jerry

Wish i could post a pic ?
Hotrod what do you think about adding a rubber hose at the end of ( standpipe ? ) on bottom of engine and running it out past the tranny ? Or ?

That would keep the draft tube from working at all. The tube needs to hang down into the air flowing under the engine at speeds above 30 MPH or so, which produces a vacuum at the end of the tube. The position and length of the tube was the subject of a lot of pretty sophisticated engineering. If it drips, the engine is well on the way to needing an overhaul. It probably smokes out of the valve cover vents or the oil fill cap at idle, right?
Jerry

Could you explain in more detail how I should install the pcv valve? I was planning on the Mickey Mouse method.

Don

If I was going to use a PCV, which I might do, I would just in install a breather cap on the oil fill at the front of the valve cover, and simply install the PCV valve in the top of the cover near the rear. I've used the same setup on many Chevy V8's that way, only on opposite valve covers is all, and it works fine.

This link to stove bolt PCV:

http://devestechnet.com/Home/PCVInstall

Deve has done all the testing and actually offers a kit of those not able to make their own.
As far draft tubes and dripping......... they dripped d from day one and do a really poor job of venting the crank case. There is really good reason PCV were introduced and your engine and driveway will thank you.....especially if you fix all those other leaks. Not to mention less fumes getting into the cab.


There are several posts on the topic on this forum.

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1257565/2.html

Having the vent and PCV on opposite valve covers of a V8 requires the fresh air to pass through the valley area. Putting them both on the same cover of an L6 means no air is drawn from the crankcase volume, where the blowby contaminants are located.

Look at the way GM chose to do the PCV, and try to duplicate their effort. Cut the draft tube off the canister that plugs into the crankcase, and weld a big flat washer into the hole that's left. Then install a rubber grommet the right size to accept a plug-in PCV valve and run a 3/8" diameter tube to the intake manifold. You'll need a vent of some type in the valve cover to let air into the engine. The standpipe canister needs to be there to prevent splashed oil at the hole in the block from being drawn into the valve as it pulls air from the crankcase.
Jerry

As far as venting the valve cover with a breather cap, I would want to weld the unfiltered 3 vents shut, that are on my 1950, or maybe a new shiny cover. And as previously mentioned on the draft tube would be a great spot for the pcv.

Okay! Thanks for the responses.
If the draft tube dripped oil from day one. There’s no way I’m going to remove it and install a pcv valve directly in the hole it came out of.

I may cut off the draft section, turn it north and install the valve there.

I may cut down the draft tube and pry the cap off and reinstall it and put the valve in the cap.

Thanks Don

I removed the draft tube from my 58 and installed the pcv valve directly into the engine block. I also made a catch can from a glass baby food jar and installed inline before the intake. There was so much oil mist collecting in the jar that I measured 6 oz. in 300 miles . I removed the pcv from the block and installed a 10 inch piece of 1 inch electrical conduit with the pcv valve in the top inside a grommet. I still used the catch can jar . I have driven over 1500 miles and have collected only about 1/2 teaspoon oil. That catch can made from the small glass jar let me see everything as the engine was accelerated. When the pcv was directly in the engine block upon acceleration of the engine there was a visible fog inside the jar ( oil mist ). Now there is nothing visible while accelerating. My engine is a 1955 235 recently rebuilt.

I installed a PCV directly into the draft tube hole in the same manner. I didn't install a catch can but noticed when I pulled the vacuum line off at the manifold oil would literally drip out of the line and out of the fitting in the manifold. I then cut the down tube portion off the draft tube and installed the PCV there, no more dripping oil. The lowerend of these engines generate a tremendous amount of oil mist by design, primarily to lube the undersides of the pistons, cyl walls and around all the rotating/moving parts.

That info was GREAT INFO ! Only a old timer would know that , I did not know it was designed for a Draft ( Duh the word Draft tube ) Thanks
P S my engine just got rebuilt this week

My PCV set ups are exactly has Hotrod Lincoln describes, not a problem over several years. Best of luck

Would you If you can post a pics of your pvc set up ?

"I have several questions about the draft tube. 1949 216 3600"

Good morning Don.

There is suddenly a lot of interest in PCV systems on this forum and I'm really interested in that too, planning one for my restored '36 Chevy pickup. What PCV valve are you guys planning to use? Are you planning to test the actual internal engine vacuum with the system installed to verify that it is in the 1"-3" vacuum "sweet spot"? Supposedly different valves create different amounts of vacuum.

How will potential vacuum leaks, for example around the oil level dip stick, be controlled?

On the '36 engine oil is put in through a fill tube on the driver's side of the block and the draft tube branches off that fill tube. The draft tube is 1 1/4" OD and is baffled from the fill tube. My plan is to branch another piece if 1 1/4" tubing off the draft tube horizontally near its junction with the fill tube and put the PVC valve in the added horizontal branch using a flat washer and a grommet (Dorman PN 42052) To try to keep an appearance as original as possible the draft tube will not be altered otherwise except to block its opening at the bottom with a 1 3/16" freeze plug (Dorman PN 555-086).

The '36 has no oil fill opening in the valve cover but it has 3 louvers in the valve cover that breathe in unfiltered air. I was planning to hide filter medium on the underside of those louvers if space allows.

Would you other guys doing this conversion be willing to share photos of your intended methods how it's going?

old55guy sent you a pm, have pics for you!

yar, I believe your '36 has a unique fill cap on the draft tube so if you don't want to butcher that one any later tube could be modified for the pcv. I was advised to use a pcv valve from a later inline with near the same displacement like a 230 or 250 inline. Re. attempting to measure the vacuum, don't see the need all I can tell you that this modification is simple and it works. We cut off the 'down' draft tube up near the top and welded in a thick washer and tapped as described.

Also, what ever old draft tube you use make sure it's boiled out or completely cleaned in some manner, most of these things are chuck full of packed crud.

JiMerit,

Is it you that has the pictures? I would really like to see them. Could you possibly email them to me?

I got this quote from another PCV thread on this forum:

Volfandt Offline
Shop Shark Joined: Aug 2012
Posts: 1,028
Knox County, TN
Originally Posted by dougs
Thanks for reply. Just so I am clear (please bear with me). I have electric wipers. I only have one port on my manifold which is now used for my disc brake booster. So can I tee off my one port and use it for both my disc brake booster and PVC? Thanks for your help.

Yes but there exceptions. All PCV's aren't the same. Some flow alot more than others. A PCV that flows too much will rob vacuum needed for your brake booster. I run a PCV on a 49 216 and it's tapped onto the same port/line as the vacuum wipers are connected. I had quite a few differing PCV's in my stash and found one that worked. It is a Purolator PV141 PCV valve. One of the PCV's fowed so much the wipers didn't even attempt to move.
Deve's tech-net site has a great writeup on adding a PCV.

According to the Deve's article measuring the vacuum inside the engine is necessary in selecting a valve that is right for the engine it's being used on.

This is an interesting subject. It's tasks like this that have kept me interested in my restored '36 pickup since I first got it in 1965. A project vehicle is never done.

yar, will get you some pics

I’m new at this and can’t offer professional advice. But as for me, I’m going to mount my valve in the sawed off draft tube hole and run it to the intake manifold. I’ve installed a vented filtered oil fill cap on my valve cover and will block the slits in the valve cover to keep out dirty air and or moisture.

Don

Anyone have an answer to these remaining questions?

Is it hollow or is there a screen or filter in it?

Is it considered a modification away from “stock original” if I remove the draft tube and go with the pcv valve?

Thanks Don

The PCV was not standard equipment on small trucks, and, it looks like it was not an RPO in 1949.

I think there was a screen near the top of the road draft tube. Maybe some knows for sure?

Draft tubes changed a bit over time old ones have a oil fill cap (make sure you have a good gasket there) . Later valve covers have an opening for a cap which could be also an air filter but your original cover will be ok.

Yes once you do this it will no longer be considered stock, but easy to change out if you are putting in a judged show.

Road draft tube is a tube (perforated) and an outer tube, no screen. Space between was for collecting oil/crud.

So, how does one remove the roaddrafttube, just grab it firmly and pull while twisting it toward the radiator. Or perhaps use a thin chisel or screw driver and separate it from the block, then pull twist?

Gently rock it side to side or use a rubber mallet and tap it side to side and pull out as you do. No need to use any other method that will damage the edge of the opening or tube.

Whatever you decide to do, please CLEAN the draft tube thoroughly prior to reinstalling it- I think they are typically FULL of junk. Both of mine were nearly completely blocked with sludge up inside the perforated baffling. I could not pass any air through one of them.

I soaked it in kerosene for a week and then used compressed air and water flushed it. Carb cleaner might work even better.... some recommend baking it on a BBQ to turn everything inside to ash, then flushing it. Once you have it off, try blowing through it, and you'll see what I mean....

Dave,

Is there a mesh/screen near the top of the road draft tube?

Yes..... there is double wall with holes.

[img]https://photos.app.goo.gl/FW4BS0nXdvQ8Zp6H3[/img]

Tim, you can see small, perforated holes at the top if you invert it and look through the tube that pushes into the block. It may have something like steel wool in there too, which would explain whyone of mine was totally blocked. I can't be sure about the steel wool though...perhaps it was only screen behind the holes?

I have a question: on my intake manifold there is a drilled and tapped hole for 1/8 npt and previously it served to power the wipers, provide vacuum for the vac advance and then around 1980 I added a third nipple to power a wolf whistle. Is this 1/8 npt hole going to be large enough for an effective pcv system or do I need to make it 1/4 npt? Or larger? Obviously adding pcv is going to lean the fuel/air ratio and obviously larger means leaner, so what say you folks? The pcv valve wants 3/8 inch hose, but a 1/8 npt connection is going to reduce that by over 50%.

Actually I have 2 questions and the second one involves an alternative approach. In Briggs & Stratton engines, crankcase vapors are simply sucked back into the engine via a pipe which connects to the crankcase and then enters the throat of the carburetor right below the air filter. There is a simple check valve to keep it from becoming a bomb in case of a backfire. The ID of the pipe that sucks the vapors in is 3/8" and that is for a one-cylinder small engine. So the crankcase vapors, water, etc go in to the carb along with clean air, are mixed with the fuel and then burned during combustion. Why would it not make sense to modify the road draft tube and then connect it straight to the air filter (inside the air filter so these vapors won't foul it) and use a pcv valve as the backflow preventer to protect in case of a backfire? The effect would be the same (that is to say you'd still be burning crankcase vapors and water vapor) but the air/fuel mixture would only be modified minimally. If you wanted, you could also easily add a common water separator (the kind used on air compressors) and you'd remove water and maybe other water soluble junk. You'd probably have to empty this frequently, however...at least I'd expect you would if you lived in a humid area. Ideas?

PCV systems have been in common use for over 50 years, with a great deal of factory engineering involved in their research and development. Why not simply try to duplicate these successful systems rather than attempting to reinvent the wheel? GM chose to use a modified crankcase ventilator with a PCV valve adapted to it when they put a closed vent system on the 261, and that system is very easy to duplicate with only a little effort. Yes, I'd suggest making the intake manifold port for the PCV at least 3/8" NPT, and the 1/2" NPT manifold port like the big rigs with a hydrovac brake booster and a vacuum shift 2-speed rear end used would be better.
Jerry

It's a few years old, but here's a link to a detailed post about my PCV install. Includes pictures :-).

talk.classicparts.com/threads/my-pcv-valve-install.16863/

Anyone know of a good source for a new / refurbed Road Draft Tube for a 235? Mine was franken-welded at some point and a bit beyond salvaging. Can't find a source (beyond ebay).

I like the research that Deve did for his PCV system. I have installed a few of them, but had concerns about the standpipe issue for reasons addressed in previous posts. Here is a simple adaptation to Deve's design that includes a standpipe that can be built for less than $10 worth of parts from the plumbing department of any hardware store. Use Deve's instructions for everything else, just add the standpipe if you want to raise the PCV out of the crankcase.

The pictures are pretty self-explanatory. The piece that has the friction fit into the draft tube hole is made from a 3/4" threaded coupling for rigid electrical conduit. The hole measures 1.25", and the coupling measure 1.27". Twirl it around a couple times on a belt sander until it taps into the hole nice and snug. The other parts are a 3/4" male NPT copper fitting, a 3 1/2" length of 3/4" copper pipe, a 3/4" to 1 1/4" copper adapter, and a 1 1/4" copper cap. The cap has a hole drilled into it using the instructions that Deve gives to add the hole to a 1 1/4" freeze plug. Just drill it into the copper cap instead. I use a step drill to get it to 7/8", then use a die grinder to do a final trim. Sweat solder all of the copper parts together, then screw the copper assembly into the turned-down conduit coupling, then tap the standpipe into the draft tube hole.

You can buy the correct size grommet at Lowes for about $.79 if you don't want to spend about $5 for the Mr. Gasket version.

I appreciate all of the work that Deve has put into and shared about his PCV system. I tweaked it just a tad by adding a standpipe. No disrespect intended. He did all of the hard work.

Matt

Matt,

What was your reason for raising the PCV valve with this extension? Was there a problem with it at a lower level? What size hard line does your PCV use?

I'm asking all these questions because I'm going to put one of these systems on my '36 Chevy engine. That's a little more complicated than the
37+ engines because the draft tube is integrated into the oil fill tube at the side of the block and there is no oil fill provision on the valve cover. The valve cover has three louvers that breathe unfiltered air. But every problem has a solution and I'll figure out a way to filter the air entering those louvers.

Yar, I use 1/4" lines.

I raised it out of concern that the suction would pick up oil splatter if it sat down too low in the crankcase. I can't say that I had a problem when I had it mounted in a freeze plug directly in the draft tube hole, but I was concerned that it would suck up oil. I raised it to avoid that.

Something that you might want to consider is to fill the vents on the valve cover, then add a fitting to the valve cover and one to the top of the air cleaner. Connect the fittings with a rubber tube. That will allow the engine to breathe clean air that has been filtered through the air cleaner.

If you want to keep the vents looking cosmetically the same (but closed), I remember reading a post on this forum that someone had filled the openings with JB Weld, then sanded them smooth. I thought that was a good idea when I read it. I seem to recall that others have filled the gaps with silicon. I have seen several conversions with the vents pounded closed and then brazed shut.

Matt

Can anyone explain if it’s not working property after installed how we will know?

Don