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Username Post: rubber hose coming out of back of block sucks air        (Topic#346671)
Eric_Gary132 
Contributor
Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
08-18-17 03:04 PM - Post#2704717    

Its like a vacuum. its by the distributor. looks sorta like a PVC valve is coming out the back of the block, with the rubber hose connected to it.

We thought it was a draft tube, but its a rubber tube that is not metal or very hard. Right now it is not connected to anything, except where it is coming from.

can anyone tell me why and for what purpose some engines have a suction hose coming out the back of the engine block?



Edited by Eric_Gary132 on 08-18-17 08:18 PM. Reason for edit: No reason given.

 
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sidworks 
Valued Contributor
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sidworks
Age: 72
Loc: Sidney, B.C.
Reg: 12-03-05
08-18-17 05:01 PM - Post#2704729    
    In response to Eric_Gary132

how many threads do you need on this ??
ron

http://www.sawmillcreek.org/showthread.php?208929-...
http://www.sawmillcreek.org/showthread.php?220902-...
http://forum.woodenboat.com/showthread.php?156542-...


 
Eric_Gary132 
Contributor
Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
08-18-17 05:41 PM - Post#2704734    
    In response to sidworks

I think probably about 132 threads, like in my user name.....kidding aside

but seriously, this is my first thread on this particular subject, because I formerly thought it was a draft tube/blow by tube, but it isn't. its sucking in air instead of blowing.

me and my grandfather are trying to figure out why the tube is sucking air, like a vacuum, and what its purpose could possibly be, since we figure it most likely is NOT a draft tube.

its got a fine looking holley 2 barrel carb and there's 2 ports/holes to connect into.




Edited by Eric_Gary132 on 08-19-17 05:34 AM. Reason for edit: No reason given.

 
Eric_Gary132 
Contributor
Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
08-20-17 07:02 AM - Post#2704903    
    In response to Eric_Gary132

heres a picture of where the tube is coming from on our engine, hope this helps. its right beneath the distributor.


https://ibb.co/eUPKMk




Edited by Eric_Gary132 on 08-20-17 07:28 AM. Reason for edit: No reason given.

 
marmst64 
Forum Newbie
Posts: 10

Reg: 11-01-14
08-20-17 08:28 AM - Post#2704916    
    In response to Eric_Gary132

Looks like draft tube was removed and i've seen that fitting/pcv valve used on many chevy 327 engines the hose is
normally connected to the back of of carb fitting edelbrock/ rochester 4 bbl.



 
raycow 
Honored Member
Posts: 26842
raycow
Loc: San Francisco, CA
Reg: 11-26-02
08-20-17 09:20 AM - Post#2704919    
    In response to marmst64

That fitting is normal on engines made from 63-68, because PCV was standard in those years. If the engine in the pic is 62-earlier, it is likely that the draft tube was removed and replaced with that fitting. However, PCV was available as as option before 63, and I believe that California engines might have had PVC as standard before 63.

On a factory PCV setup, the line from that fitting is connected to a PCV valve and the other side of the valve is connected to either the carb or the intake manifold.

My feeling is that Eric has some other point on the engine (like maybe a valve cover) connected to a vacuum source and that is the reason for the apparent suction at the fitting in the pic when the line is disconnected. However, that is only a feeling and is worthless without proof, like pictures showing what is connected to the valve cover(s). I have asked Eric for pictures, but he has been remarkably economical in posting them so far.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Eric_Gary132 
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Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
08-20-17 09:58 AM - Post#2704923    
    In response to raycow

https://ibb.co/h2iCGa

circled in red with the arrow is hole where the shop connected the tube to.

we found that the hose on drivers side, the front of the valve cover, is running into the carburetor. (the hose right behind the alternator).

https://ibb.co/nq05qQ



Edited by Eric_Gary132 on 08-20-17 10:00 AM. Reason for edit: No reason given.

 
raycow 
Honored Member
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raycow
Loc: San Francisco, CA
Reg: 11-26-02
08-20-17 10:49 AM - Post#2704934    
    In response to Eric_Gary132

Eric, thank you for the pictures and descriptions. Those pretty much show what I was looking for and may provide the answer to your problem.

The connection on the driver side (from the valve cover to the carb) is probably ok PROVIDED that you have a PCV valve in that line. The picture does not show enough detail for me to tell whether it has a valve or not. If it does not, then you MUST install one.

There are two ways you can deal with the other line.

1. This will produce a "closed" system and is preferable because it will keep the outside of the engine cleaner:
Disconnect the hose from the passenger side valve cover and plug the opening in the cover. Leave the other end of the hose connected to the fitting at the rear of the engine. Connect the free end of the hose to your air cleaner inboard of the filter element. Most air cleaners which are large enough in diameter have a provision for this. I can't tell on yours because the top side does not appear to have a connection and I can't see the bottom side. This line MUST NOT have a PCV valve in it.

2. This is an "open" system, to be used if your air cleaner does not have a hose connection and you do not want to replace the air cleaner:
Leave the hose connected from the fitting at the rear of the engine to the passenger side valve cover. This line MUST NOT have a PCV valve in it. If it does, remove the valve. REPLACE your present sealed filler cap with a VENTED one.

After making the necessary connections for either (1) or (2), you may need to readjust the idle speed and mixture screws on the carb to achieve a satisfactory idle. Normally you would use a vacuum gauge and adjust for highest vacuum at an idle speed which you find acceptable or which is specified for your engine. Do this only after the engine is fully warmed up.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Eric_Gary132 
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Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
08-20-17 04:44 PM - Post#2704978    
    In response to raycow

.



Edited by Eric_Gary132 on 08-20-17 06:31 PM. Reason for edit: No reason given.

 
Eric_Gary132 
Contributor
Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
08-20-17 08:48 PM - Post#2705001    
    In response to raycow

A relative of ours said we could just plug the pcv suction tube with a bolt so dirty air doesn't get sucked in there. Also, since it may not even be used.

Is that a good idea? Or will sealing the suction tube off harm the engine?



Edited by Eric_Gary132 on 08-20-17 08:51 PM. Reason for edit: No reason given.

 
raycow 
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raycow
Loc: San Francisco, CA
Reg: 11-26-02
08-20-17 11:41 PM - Post#2705016    
    In response to Eric_Gary132

If you just plug the hose and leave everything else the same, where is your air inlet source for the crankcase going to be? PCV requires inlet air in order to work as it is designed to. And you want that air to pass through some kind of filter before it gets into the crankcase. Otherwise, suspended particles in the air are going to cause increased wear inside the engine after they get in. That filter is going to be the air cleaner on the carb with the closed system, and the wire wool (or whatever else is being used now) inside the vented cap on the open system.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
jktucker92 
Silver Supporting Member
Posts: 93
jktucker92
Reg: 02-05-17
08-21-17 06:37 AM - Post#2705059    
    In response to raycow

The pictures do help quite a bit. In any case, you will always have several options for a SBC, because the factory made several changes over the years. While a road draft tube will allow the engine to run fine, the PCV system is better. That said, you need one and only one PCV valve. Until '69, the valve covers had no holes, and the PCV valve was connected at the back as shown in your first picture. After that, the factory put the PCV valve connection in the valve cover and didn't machine for the port in the back. Since it appears you have a PCV valve in the valve cover on the driver's side that is already connected to the carburetor, it's probably convenient to leave that in place. If you choose to use a PCV valve in the valve cover, you must plug the port in the back. That can either be done with a rubber plug, or you can remove the port entirely and put a freeze plug there.
Engines also typically have a breather of some sort. Engines that had an oil filler in the intake manifold typically had a breather there, while engines that use the valve covers as the fill typically had a port in the valve cover that went to the air cleaner. When using aftermarket air cleaners, it's common to put a breather in the valve cover, where the circle is on your hole_in_valve_cover picture shows. If the existing cap has a hole for a tube in it, that is what you would connect to the air cleaner. You can either connect a hose from there to the air cleaner (if your air cleaner has a port for it), or you can buy a breather cap and put that in its place.
Now, the only piece of information you've mentioned that doesn't make sense is that there is vacuum present at that port. Since that port goes into the oil gallery, that doesn't make much sense. Is the vacuum there when you disconnect the hose at the back of the engine, right at that port? If so, the only explanation I can come up with is that there must be a significant leak in the intake gasket and you are pulling air from the oil gallery. Unless, as mentioned above, there is another hose connected to that port that is connected to the carb and providing the vacuum signal, there is no other way for vacuum to be present in that location.



 
raycow 
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raycow
Loc: San Francisco, CA
Reg: 11-26-02
08-21-17 08:18 AM - Post#2705070    
    In response to jktucker92

  • jktucker92 Said:
Now, the only piece of information you've mentioned that doesn't make sense is that there is vacuum present at that port. Since that port goes into the oil gallery, that doesn't make much sense. Is the vacuum there when you disconnect the hose at the back of the engine, right at that port? If so, the only explanation I can come up with is that there must be a significant leak in the intake gasket and you are pulling air from the oil gallery. Unless, as mentioned above, there is another hose connected to that port that is connected to the carb and providing the vacuum signal, there is no other way for vacuum to be present in that location.


It took a while to work that one out, and Eric's pictures show the reason for the problem if you examine them closely enough. If you look at the driver side valve cover, it has a hose running to either the carb or the intake manifold. That's the vacuum source which is creating suction at the port at the rear of the block.

Eric's "repair shop" connected a hose from the rear port to the passenger side valve cover. You can see where he drew a red arrow pointing to the valve cover where the hose was connected. This left the engine with no outside filtered air inlet to the crankcase, so the PCV wasn't working properly.

Several knowledgeable members here on the forum have already put in a lot of time and typing concerning the problem in this and other threads on the same subject and suggested good solutions. However, as the saying goes, "You can lead a horse to water....."

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Eric_Gary132 
Contributor
Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
08-21-17 08:27 AM - Post#2705071    
    In response to raycow

ray, we found that the hole on the passenger side valve cover is blocked off underneath by solid rubber. we stuck our finger in there and there is no route or anything, its like a wall, so i am not sure what that is about.



 
raycow 
Honored Member
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raycow
Loc: San Francisco, CA
Reg: 11-26-02
08-21-17 08:53 AM - Post#2705073    
    In response to Eric_Gary132

Ok, we are slowly getting useful information here. In that case, your easiest route would be to plug the port at the rear of the block (or just plug the hose) and replace the sealed filler cap with a vented one. Any decent parts store should have such a cap, but if they are clueless, show them this picture:
http://mgaguru.com/mgtech/accessories/pi cs/oil_cap...

This will give you the functional equivalent of option 2 - an open PCV system. Don't forget, you still need to see if there is a PCV valve in the line from the driver side valve cover to the carb. If there isn't, then you must install one.

Ray

Those who choose an automatic transmission want transportation. Those who choose a manual transmission want to drive.


 
Eric_Gary132 
Contributor
Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
08-21-17 02:12 PM - Post#2705110    
    In response to raycow

silly me, i just was at my grandfathers house and I realized that the valve cover hole on the passenger side actually has a plug in it, what i was looking at in the pictures and in person is not the actual hole...but a plug

the former owners put a plug into the hole already and the shop plugged the suction hose into the plugged hole, which was a dumb move lol.



Edited by Eric_Gary132 on 08-21-17 02:13 PM. Reason for edit: No reason given.

 
Eric_Gary132 
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Posts: 222

Age: 24
Loc: northern California
Reg: 01-27-17
11-14-17 04:01 PM - Post#2714379    
    In response to Eric_Gary132

You say to plug the port at the rear of block, but this port is siphoning air, just like a vacuum cleaner.

Won't plugging it off cause some sort of stress to the engine? The air suction from it will have nowhere to go if it's blocked off.

I'm just going to plug this suction hose/port with a mini air filter.



Edited by Eric_Gary132 on 11-14-17 06:45 PM. Reason for edit: No reason given.

 
jktucker92 
Silver Supporting Member
Posts: 93
jktucker92
Reg: 02-05-17
11-15-17 07:36 AM - Post#2714467    
    In response to Eric_Gary132

Something is wrong if there is a large amount of air being pulled in at the PCV/road draft tube port at the back of the block. That means that the lifter gallery is at negative pressure (vacuum). Attached is a photo of the back of the block with the intake removed. That port should have a oil separator connected to it, which just prevents oil from the lifter gallery from being sucked into the PCV valve. The pressure at that port should be the same as the lifter gallery. One way I can see having negative pressure there is if there is a large vacuum leak, probably at the #8 intake port at the gasket between the intake manifold and the head. It's also possible to have a crack in the intake manifold itself. I've also seen threaded ports in the bottom of some intake manifolds that are plugged with pipe plugs. If the plug was missing it could also cause negative pressure there. In any case, you generally should have a small positive pressure at that port caused by blowby at the cylinders since they will never perfectly seal. That pressure is relieved by the vent either in the valve cover or filler tube. I had a '65 327 that was so worn out that the oil filler cap would be blown off the filler tube at high RPM's because of the amount of blowby that engine had.

Attachment: PCV.jpg (10.81 KB) 3 View(s)






 
Eric_Gary132 
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Loc: northern California
Reg: 01-27-17
11-15-17 08:34 AM - Post#2714476    
    In response to jktucker92

Thanks for the help. So then it's not a good idea to plug it then, right? Especially if it's sucking air in?


The suction isn't really strong but it's enough to feel it with your hand.



Edited by Eric_Gary132 on 11-15-17 09:36 AM. Reason for edit: No reason given.

 
jktucker92 
Silver Supporting Member
Posts: 93
jktucker92
Reg: 02-05-17
11-15-17 09:46 AM - Post#2714487    
    In response to Eric_Gary132

The bottom line is if it's sucking air in, then you need to fix that problem first. If you're not using it for a road draft tube or PCV valve, it should be plugged. If you intend to not fix the vacuum leak and run it as is, you will eventually burn a valve because the excess air getting into one or more cylinders will cause it to run lean which will burn a valve. If you leave it open, it will just suck dirty air into the lifter valley and into the source of the vacuum leak. If you plug it, it will suck air through the breather and into the vacuum leak. Either way, there will be bigger problems down the road.



 
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