The Stovebolt Site Forums The Shop Area Engine Shop Road Draft Tube

OK...another question about PVC items..If you have a road draft tube and a open breather cap like a stock set up AND on the valve cover a PVC from valve cover to intake maifold and you get rid of that annoying oil bath air cleaner and replace it with paper from Jim Carter have you done good or bad?...Or, same set up but block the draft tube internally and have it on just for looks? THANKS, STEVE

Steve,

Are you referring to a 1954 original engine, valve cover, and oil filler cap (which did not breathe in 1954)?

Also, I think that the PCV set up on 1954 235/261 engines did not have a tube from the valve cover to the intake manifold. A diagram is at the bottom of this page.

[Your profile shows you have a 1954 1300 1/2 ton. Maybe a Canadian Chevrolet had a different set up?]

Tim

Sorry.. forgot to include 1954 truck 3100 with a 235 1955 1st series engine and drive line...what I want to do is get rid of the oil bath air filter and install a PVC valve. I have been looking around at other post and there has to be at least 20 diffrent opinions and ways of doing it...just trying to get opinions and thoughts on the subject. THANKS tclederman

The pcv setup will let you loose the driveway oil slick caused by the draft tube. You can replace the draft tube with a plug, plug the end that's in the block, or cut off the side tube and weld in a piece.

The engine will need an air intake to the crakcase. Either leave the open breather cap or add a hose from the valve cover to the air cleaner, most leave the breather cap in.

Fred...good idea... There is a post from Beaver 52 where he cut the draft tube at the elbow welded in patch and connected his PVC valve there to intake manifold..but upon reading all the post it seems in the long run a road draft tube is the best way to go with a valve cover breather cap...no oil slick in drive way if you have a drip pan...THANKS, Steve

If you go with a PCV system you MUST use a filter with a collector and drain.
You can make one yourself but they are also available online.
It works by condensing the heavy crankcase fumes into liquid form inside the filter canister.
It fills up really quick and needs to be drained every few hundred miles.
You have to see for yourself how much nasty stuff the crankcase produces.
You would never introduce this into your intake on purpose.

Despite the filter a pcv system will produce a hard crusty build up inside the combustion chambers after a few thousand miles already, decreasing performance.
Another drawback with these systems is they stop working when the engine produces most of the crankcase vapors - under heavy load or prolonged high rpm.
Without the road draft tube, the increased crankcase pressure in these conditions is hard on the seals and rings, let alone escaping oil vapor makes a constant mess of a clean engine.

I have used a filtered closed PCV system daily for a few years and am now going back to the road draft tube with a dedicated valve cover filter.
I found that crankcase vapors shouldn't be anywhere near the intake of my engine and that increased pressure on the freeway needs to be evacuated.
If the road draft tube can't do this efficiently, I may use the exhaust as the last resort.
There are crankcase evacuation kits available online where the exhaust sucks out the vapor pressure at higher rpm and eases piston travel at the same time.

when installing a pcv in an older unit you are creating a vacum leak so be shur to size the valve to the engine and you have to tap the intake vacum for pcv and you will have to close all external such as road draft and VC use only pcv to control engine preasure,,tap valve into VC and install baffels to control oil loss thru valve..you can install intake line to air cleaner from VC to help you will also have to baffel to control oil loss but I don't think this is a must...doc

Hey that's what I have been reading about PVC valves and combustion chambers...Do you think it would be OK to leave the draft tube working ( when I find one) and a breather cap on the valve cover and a paper type air cleaner set up? Or should I leave oil bath air cleaner hooked to the valve cover an no paper air cleaner? Also one post said PVC are better as the guy gets oil on his clutch from the draft tube....I think Chevy would have figured that one out when they built them? THANKS, Steve

How bout plugging the Draft Tube at the bottom. (Pound in a wood plug). Drill an appropriate hole in its flat circular top. Install a PCV valve there and route into the exhaust manifold where appropriate. My Fentons have a couple of tapped holes already.
Too simple?

OK....another idea....I don't enough about the subject matter to respond that is why I'm gathering all this info...I still think the draft tube and no PVC is the way to go..but I still need to know about air cleaner set- up paper/oil bath....leave alone? Disconnect ? THANKS for your information, Steve

I use K&N filters on my carbs, completely disconneted from the valve cover.
You can clean and reuse them. They are also more efficient than paper.
I also use a dedicated valve cover filter by K&N - The typical breathers stuffed with some foam are not very efficient.

Using the exhaust for crankcase evacuation is basically like a mini road draft inside the exhaust pipe after the collectors.
A small tube is welded inside the exhaust pipe with its important angled cut end facing away from the flow, just like the road draft tube.
The pressure difference at the cut angle sucks out the crankcase vapors. A regular check valve prevents exhaust gases from flowing back. A PCV valve is only needed to limit flow when used with manifold vacuum.

This system is more efficient at higher rpm and somewhat like the opposite of a PCV system which is most efficient at idle and cruising.

I thought PVC was plastic.

TINY..... laugh, thought I'd never start.....PCV is the correct answer and thanks for playing! Steve

If the engine is in good condition all factory breathers aes fine..Use what filter sys on the carb you feel good about,,the oil bath is fine if you are willing to keep it serviced..Some of the cleaners werenot oil just a screen to stop large chunks so if that is what you have replace with paper unit...Why go to the work for PCV and retain all org factory ,,in order for PCV to operate correctly system should be closed...PCV in the top of the road draft might work good I don,t know,,it would save some work redoing the VC...doc

I know some of you know what is happening here, but IMHO - If oil on the driveway is your concern, then the old rope seals, oil pan gaskets, timing covers, etc will need to be updated with new gaskets, seals. The road draft tube modification to a closed PCV system will not be enough on its own.

If you are trying to update the breathing system, take the easy way out and either lengthen the draft tube to the rear of the vehicle, put a filter on it, or both. You can filter the air more efficiently without changing the way the engine breathes.

It the modification isn't really understood, I would be careful. One should understand how the enigne breathes first.

Filtering where the air comes in and out is what is going to save the engine life from small dust particles. Blocking a part of the system incorrectly can give you a new problem to contend with.

OK..options for the most orginal looking / working set ups:

1. Leave whatever air cleaner alone with hook up to valve cover..yes/no

2. Replace oil cap filler to non-breather.. yes/no

2A. Close all holes (previous attempts at smog ) in valve cover except the air cleaner hook up..yes/no

3.Install road draft tube with out modifications and NO PCV valve..yes/no

Option two:
1. Leave air cleaner hooked up to valve cover yes/no

2.Replace valve oil cap with non-breather and close off any other openings to the valve cover, leaving the air cleaner as the only point of air introduction to the engine..yes/no

3. Close off bottom of draft tube and connect a PVC valve (some how ) to upper portion of road draft tube and run line to intake manifold vacumm port with or without a TEE connection, if you have electric wipers no TEE needed yes/ no

Option three:
Same as two with the diffrence of insted of vacuum port on the intake install weld fitting to exhaust pipes down stream and connect PCV line there yes/no

If you reply in the negative please give us a reason with the best answer...all opinions will be considered and tabulated and then we can all do what we think is correct and in that way we can all be right. THANKS, Steve

You are the one,,all info given on this is to help you make a jugement as to what you want,,if you ask 5 people you will get 5 versions on it..doc

Doc...I'm not the only guy out here in California that has had an engine from the 50's cut up to meet the tuff smog standards. I thought I would post in the Q/A format so you fellers with all the knowledge about these trucks could help us out with that knowledge base. In this way we can make informed choices....at the close of the day you are right, it's all up to personal choice....but the more options the better! Thanks, Steve

Steve,

Just to complicate your options: does your valve cover have four slits/slots in the top (as was found on 54/55-1st non-PCV engines)?

If you have the slits, you can use the vented oil filler cap or the original non-vented oil filler cap but no PCV system (the slits in the valve cover and/or the vented oil filler cap do not allow the PCV system to operate properly).

If you do not have the slits:
- you should use a vented oil filler cap with no PCV;
or,
- you should use a non-vented cap with a PCV system.

As doc41 suggested, do what suits you. If you want an opinion about original appearance:

- Use an original PCV set-up for 54/55-1st (hosed-draft tube, hosed air-cleaner/valve-cover, and non-vented oil filler cap);
or,
- Use an original non-PCV set-up (non-hosed draft tube, non-tubed oil-bath air cleaner or wire-mesh air cleaner, and matched valve cover and oil filler cap.

Nothing like a clear, concise answer, right?

Tim

I now have pics of the system I used on my 53 3100.If anyone would like to see it you can E-Mail me as I don't know how to post pics here. It is as close to orgional as it can be.

TIM...its so clear now I can see the light at the end of the tunnel...just one thing, on your "matched valve cover and oil filler cap " we have no idea of what that means. Perhaps... breather cap or non- breather...and no other openings on valve cover except of course the oil fill hole? Will you illuminate? Thanks, Steve

Yes, not knowing if you have slits in your valve cover:

- slits in valve cover matches not-vented oil filler cap;

or

- no slits in valve cover matches vented oil filler cap

Tim,
some of us ( I'm speaking for three people who do not type ) have slits on their covers and some not.. so your answer is perfect... and we thank you! Steve

...we have a desenting vote..we have a person who has a hose from air cleaner to valve cover and a breather cap and a draft tube NO PCV and he says that you can have both the air cleaner and the breather cap on a non PCV( draft tube ) set up as it makes no difference and in fact improves air circulation?...Got me, I just do the typeing. Steve

Steve,

Who am I to argue? Hey, are you all drinking beer, etc? I wish I was in SF to chew this over with you.

"OK..options for the most original looking / working set ups:"

1954/55-1st?

"we have a desenting vote..we have a person who has - a hose from air cleaner to valve cover
- and a breather cap
- and a draft tube NO PCV

and he says that you can have both the air cleaner and the breather cap on a non PCV( draft tube )"

What does non PCV ( draft tube ) refer to?

There never was a 54/55-1st non-PCV with a hose from the air cleaner (to anywhere). Now, I think you said that you might have a newer engine (can you post the casting code or the engine serial number)? What year do you want it to look like?

Tim

Tim,
Thanks...for your help....now everyone is happy...but me as I need another answer to MY radiator question about X bracing... and those who are not happy can learn to type and send their own questions! Steve....PS. SF... we are out of SF about 35 miles to the South near the ocean. No beer has been consumed as the typist i.e. me has had enough of people shouting their ideas to me and I can't do that and drink beer.....I did my basic training for the Army in Fort Dix New Jersey and saw the big apple...up-state was very nice.

Engine casting number...3837004= 1955-57... engine head 383684 gm 28 = 1956.. The owner died and they had no info. on the truck so we do not know what was/was not done that's why all the research plus my buddies both own a 1948-50 3100 both of which are not stock and one stock 1954 150 miles from here. We are setting the truck up to look like 1954.

you will have to find out what the state will accept,,I have no idea what... I was of the opinion that older cars if left unmodified were exempt...If you are going PCV then close the engine and install a PCV..doc