PCV valve for road draft tube block SBC

Many may already know this, but, I'm working on my first SBC with a oil fill and road draft tube set up. I want to convert it to a PCV valve from the road draft tube. Just found out, accoridng to the "how to" book I'm using, that the hole in the back of the block where the road draft tube is currently is the right size for the PCV and grommet from any 63-67 SBC, which is a direct replacement for the road draft tube.

I've got my hands on the PCV now if I can just find the grommet I'm in good shape.

 

This is the way Chevrolet did it in 1965. PCV is a screw in type on a fitting on the back side of the carb. Hose runs from the PCV around back to where the road draft tube was.

 

Check the 64-67 Chevelle motors for the special PCV hose fitting that is held in place by the same 1/4-20 bolt that held the road draft tube in place. There may be a special rubber grommet for that hole but I've never seen one. (to my knowledge)

 

I just did a '59 283 that way for a friend. I used a grommett for a Ford V-6 at least that's what it said on the grommet box at NAPA. Perfect fit.

There were some fitment problems with the stock baffle and the front fill edelbrock edelbrock intake. We pulled the stock baffel and made a baffel out of a soft plug with 4 3/16 holes drilled in it. Works like a champ. I don't remember what size soft plug it was but if you need one you can take the stock baffel up to the parts counter and that can match one up for ya.

 

I have a 63 vette motor in my 50 F1 I got a grommet froma bbc chevy valve cover and put a copper fitting in it and a 45* and ran it under the air cleaner I the drilled the oil fill and put a threaded bung in it that I screwed the PVC valve to and ran it to the vacuum into the carborator. no holes in the vlave cover and looks clean and works fine.

 

on my 327 there was an opening for a road draft tube.i've heard of people drilling freeze plugs and stickin a PCV in there,but i just got the rubber grommet that comes for valve covers (the full one without an opening already in it) and punched a hole in that and stuck the PCV in there with a line to the carb.not running an oil tube till i get another intake (my God that Moroso valve cover on the one side looks hideous!) and no problems yet..i put solid script covers on it with NOTHING in the rear opening and drove it around 60 miles down the highway before she started smoking and shootin oil!
creepy

 

I think Chevy put the PCV both ways: 1) to the road draft tube hole in the reat of the block, and 2) to the oil filler tube in the front of the intake.

If anyone wants it, I'll try to remember to take a pic of the original Chevy piece that bolts in the road draft tube hole. Has a nipple on it for the hose.

I still have the original GM boxes and part #s for the painted and chrome plated oil filler tubes, with threaded bungs already installed, and the screw in AC PCV part# for set-up #2.

With any of these set-ups ya' still need to install the baffled breather can inside the engine. If ya' don't, excess oil will be coming outa' that road draft tube hole. How do ya' think I know that??? . Nope, it didn't happen to me, but it did to one of my buds that had a "PRO" engine do his work for him. Some pro guys don't know squat .

 

Cool, I'd like to see pics of that set up, and get part numbers from you for the oil filler tubes.

I'm curious, why would they have a PCV valve pulling vapors from both the front and back of the crank case? Seems like at the back where the oil draft tube was, bulling air out, and air going in the oil fill tube would be the kind of cross ventlation you would want.....was it purely an emissions thing?

 

Think ya' misunderstand, or I wasn't clear enough.

They used one or the other, but not both on the same engine.

I have a 1967 AC POSITIVE CRANKCASE VENTILATION Wholesaler's and Dealer Catalog in my hand as I type this.

There is Four types of systems:

1) Road Draft Tube System: No PCV, vented oil filler cap, road draft tube. Starts to work at 20+ mph.

2) Open System: Standard vented crankcase breather oil filler cap on oil filler tube. Hose from old road draft tube hole with a PCV to bottom of carb. Works at idle.

3) Closed System: Approved for use in California 1964. Sealed oil filler cap. Hose from filler tube to air filter housing. Hose from old road draft tube with a PCV to bottom of carb.

OR... it could be reversed. PCV on oil filler tube with hose to carb and hose from old road draft tube hole to air filter housing. Don't think the engine knows the difference from in or out with this system.

AC sold kits to convert older cars to this system.

This let's ya' run those old Corvette script V/C's without whacking them up.

4) Dual Action System: Not going there .

I'll try to remember next time I'm at my shop to take pix and get ya' part #s. It's all probably available as repop parts from Corvette restorers parts suppliers.

I just happen to buy this stuff 30 years ago. I installed parts like this on my 327 powered '55 Chevy. Still have the car and all the extra parts I bought. Don't know if the part #s are still valid.

 

modifieddriver, thanks! That explanation really helps a lot.

 

If you have a lot of money the corvette catalogs show an already set up system with the filler with the pcv valve and I believe the fresh air in at the road draft. Lots of doe though. ED but can get an Idea on how to set it up as I did. ED

 

OK, Done. Here is what I did:

I found the grommet and PCV valve just hanging on a hook out in the open at my local O'riley parts store. I have attached pictures below, showing the PCV valve, the grommet and the packages they came in with part numbers clearly visible for any one who needs to do the same thing. Other than that I had the kid cut me three feet of PCV hose that fit the valve.

I pulled not one, but two, freze plugs out of the hole in the back of the block (don't know why they pushed two freze plugs in the road draft tube hole), greased the grommet up with white grease, shoved it in, attached one end of the hose to the PCV valve and shoved the valve into the grommet. Now air should enter the crank case through the breather on the top of my oil fill tube at the front of the block and be sucked out by the PCV valve at the back. I'll hook up the other end of the hose to the carb.

 

OK, here's the pics I promised. Better late than never.

This is the stuff ya' need for a closed system, excluding the nipple on the air filter base. That comes with a custom air filter kit.

Send questions if ya' need to.

 

The parts numbers are a little tough to make out, could you post a list of them?

 

Here ya' go. Remember, these could be obsolete #s:

Chrome tube: 3889316

Painted tube: 3889311

Oil Cap: 3851735

PCV: CV726C (6422721)

PCV: CV590C

I don't have a part# for the rear mounted 90 degree nipple.

 

I drove my truck around some this weekend. After I put this PCV in the drip from the filter cap on my oil fill tube stopped, and that alone was worth it.

 

Any reason why you couldn't run it from the draft tube port to the vacuum port on the intake manifold?

 

the later ones had a fitting that bolted over the hole in the block (like the road draft tube) and had a short nipple then you would just use an inline pcv to the carb.

 

Am I correct in thinking that later small blocks didn't have a hole in the back where the tube went? I was thinking of drilling and tapping a hole in the back of the intake manifold for a screw in PCV.

 

I used a bbc valve cover pcv rubber bushing in the draft tube and used copper in the rubber and a tube to the intake vacuum. I then for my 327 engine with no holes in the valve cover silver soldiered a female bung in the fill tube of the offenhauser intake and screwed in a pcv valve with a tube welded to the bottom side of the air filter and has worked fine for several years.

with out the fill tube I would have run the pcv off the draft tube and put breathers in the valve cover.

 

I ran a breather cap on the oil fill tube and Moon breathers in the valve covers. I also put an expansion plug in the hole for the Road Draft tube. I never had any problem with oil blowing out of the breathers. Please feel free to tell me I'm an idiot.

 

I doctored up the RD tube and ran an inline pcv from it used a breather on the fill tube

 

I found an old oil fill tube with the bung and PCV in it, so now I'm running a system kind of like Modifieddriver suggested. I've got the PCV screwed into the bung on the oil fill tube and stuffed a rubber grommit and breather into the road draft tube hole. Should draw filtered air in through the breather (its the kind with the baby K&N filter on it) and the air should exit out the PCV on the oil draft tube and get sucked into the carb. I ran a line from the PCV directly to the front of my Edelbrock. Seems to be working.

 

I just wanted to say that this post is great! I ran into this issue last night. Now I know what I need to do! Thanks Luck Strike!

 

I used a Fram FV-113 PCV inline from the road draft port to the front on the carb base. (This may have been an older n.o.s. PCV..I forget.) The dude from Edelbrock told me to use the front hole of the carb, not the rear. I have had no troubles with it, although I did originally remove & clean the tin can under the intake that leads to the road draft port.

 

Heres what picked up...






And this is how it turned out....




Via TJJ on iPhone

 

Yes, that's the way they did it in the back of the engine,

BUT........what are you doing in the front of the engine?

Could be 1)a filler tube with a vented breather cap or 2)a filler tube with a sealed oil filler cap and a fitting for a hose going to the air filter base.

Each works, but #2 is the better deal.

 

Any tips on running this setup on a 409? I have a breather on the oil fill tube, but right now have absolutely nothing for a road draft tube. I was thinking of eliminating the RDT all together by plugging the hole and installing a PCV valve in the plug, then plumbing a hose to the carb. Done. Should work right?

 

If I may add a little to this thread, GM did put the PVC in the back of the carb and on other models & years in a fitting welded to the filler tube, BOTH are wrong, yes this was factory but caused a lot of grief because the oil would not drain out of the valve while the car sat & eventuality sludge would form and the valve no longer functions. The fix was to put the valve upright in the back of the block in a grommet. It can also be installed anywhere in a hose but standing upright only.