Oh John, be very careful and don't blow up the poor guy's engine.  Should the intake manifold's pressure be higher than that of the crankcase (which can happen in a turbo charged engine or under certain conditions, such as an intake backfire), the PCV valve closes to prevent reversal of the fuel mixture into the crankcase.

I didn't stutter when giving that advice.   Ford had Paxtons back in Y-Block days, but they separated intake from crankcase gasses.  If intake pressures EVER get higher than crankcase, that valve is not supposed to inject even the smallest amount of blended air/gas mixture into the crankcase.  In fact, if the PCV doesn't stop like a check valve, DON'T USE IT!

You may have missread your manuals, John.  Could you scan those sentences to share with us?  I think you are confused about when the PCV operates at idle speed (most vacuum) and 'most restricted' flow.  I'm sure the manuals are calling this condition a controlled orfice.  As the vacuum goes down under normal driving speed, the valve lets more crankcase air in.  At Wide Open Throttle (zero vacuum), the PCV is about useless.

Dave Dare

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Dave:

I have 3 Paxton blown '57 Fords.  Of course the intake is separated from the crankcase. There weren't pcv valves in '57.  All three of my cars are equipped with road draft tubes.

As for the manuals, I didn't mis read them.  Sorry, I can't scan, but I'll mail you copies if you need to see them.  Do you have access to any Ford manuals of that era?  Remember, except for Corvairs and Olds F-85s, there weren't turbocharged cars then.  Corvairs had draft tubes, I don't know about F85s.  My GM manual is Buick, no turbos in '65.  No turbo '68 Fords either.  That's why there wasn't a section in the manuals about pcvs and turbos.  I stand by my statement.  Thanks for your input.

John - "The Hoosier Hurricane"

You cited reference to two service manuals but are unable to share the wording about PCV valves from them, and you are absolutely SURE you didn't misread about the operation of PCV valves.  I guarantee NONE of them indicate the PCV valve allows fuel mixture into the block area.

John, this is a VERY serious safety issue (at Ford Motor, we classify it as 'double-inverted delta'), the highest, most lawsuit-prone concern.  We ALL need a full understanding of how a PCV works and how explosive 14.7:1 Air/Fuel ratio is.  The possibility of mixing fuel mixture into a block cannot happen.

Whether naturally aspirated or not, the bottom end of a crankcase can be like a flame-throwing  blowtorch, especially in old engines.  All of our Y-Blocks are old, now.  I tore mine down and measured ring end-gaps of .200".  By design, piston rings rotate.  At some point they all align for a time, sucking oil up and shooting flames down.

Since backfire alone can be dangerous, PCV valves close completely in one direction (like a check valve) preventing air/fuel mixture from entering the crankcase.  ALL of your manuals will explicitly indicate this.  According to your statement, you need a better understanding of how a PCV valve operates:

  Absolutely NOT TRUE.  Nobody can predict a backfire.  John, you need to retract this and rethink how things really work.

If you need further references here they are.  Click on the wording for each link:
"Operation: Should the intake manifold's pressure be higher than that of the crankcase (which can happen in a turbo charged engine or under certain conditions, such as an intake backfire), the PCV valve closes to prevent reversal of the exhausted air back into the crankcase again."  - http://en.wikipedia.org/wiki/PCV_valve

"One really comforting feature of the PCV valve is its behavior in the event of a backfire. If your car backfires in the manifold, the pressure makes the spring close the valve completely. With the valve closed, there is no chance that the flame can move into the crankcase and cause an explosion."  http://www.innerauto.com/Automotive_Systems/Exhaust_System/Pcv_Valve/

"The PCV valve controls the amount of vapors pulled into the intake manifold fromt the crankcase.  It also acts as a CHECK VALVE by preventing the flow of air from entering the crankcase in the opposite direction." - Pg.24 Chilton's Repair Manual (Part No. 8314) Thunderbird/Cougar 1983-92

This is straight out of one of my Chilton's manuals.  I've asked you to share with us, your reference manuals.  The invitation is always open.

Dave Dare

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Dave.  Here are the picture posting instructions in case you missed them in the past threads.

Generalized picture posting instructions

For those of us on dial up, your particular picture hosting site inhibits the threads in which you insert picture links from coming up in a speedy manner.  Thanks.

Lorena, Texas (South of Waco)

Ted, the pictures don't exceed 600 pixels wide, have a hard return before and after, and my host server is Comcast.  Comcast is known for fast speed, but on occassion, they are slow or they go down, during maintenance.  Dial-up users will never see color pictures very fast, especially if their baud rate is lower than 56K/sec.  Does anyone NOT see any of my pictures?  If so, let me know. Thanks for the 'heads-up' Ted.  I'm surprised I haven't heard from Hoosier John, yet. -  Dave

Hey, BTW- http://www.y-blocksforever.com/forums/FindPost26072.aspx this thread has several color pictures at 800pix wide.  Both Ted and Hoosier are moderators there too, but I didn't see a complaint about dial-up.

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Dave, you haven't heard from me because I'm dealing with a pre-64 Y block and late '60s era pcv systems, not emission controlled '93 model cars.  Crucify me if you want because I don't have the equipment to copy and send stuff electronically.  I offered to snail mail the pages to you, but never received any hint you wanted them not any address to send them to.  My last statement on my previous post says what I mean to say about it.

John - "The Hoosier Hurricane"

John, I simply asked you to quote the description of your PCV valves from your reference pages.  You refused to do that because the words would prove you wrong.  I don't care who is right or wrong.  What I care about is preventing personal injury from an exploding engine.

Two references I cited above are not year specific.  PCV valves haven't changed, either.  They vary in size and configuration (straight or ell, threaded or not), but they all work exactly the same way.

Retrofitting a new PCV to an old engine block is easy, but must be done properly.  If you had a good understanding of the operation of any generic PCV, you would not have made your false and dangerous statements.  Do your homework and never criticize correct safety information.  I only pray nobody gets hurt.

To my fellow Y-Block restorers and enthusiasts:
PCV's rarely get changed because they last so long under normal wear.  Some books ask you to rattle as an indication that it is still good.  That is NOT a good indication because the spring can be broken (and it will still rattle).  Also, make sure your PCV blocks in the backflow direction to prevent explosive gasses from entering your block.

Dave Dare
Ford Motor Co., Dearborn

Royal Oak, Michigan (Four miles north of Detroit, and 12 miles NORTH of Windsor, Canada).  That's right, we're north of Canada.

Ford 292 Y-Block major overhaul by simplyconnected

Dave:

I did not refuse to quote because I would be proven wrong.  I'll go ahead and quote, but you still have the option of telling me again that I can't read, or that I changed the wording.  Here goes, 1968 Ford/ Mercury manual, section 8-33, under the heading "CLOSED CRANKCASE VENTILATION SYSTEM": The first part of the explanation tells how the air gets into the crankcase and how it circulates within it.  Do you want that quoted too?  Then it continues:  "During idle, intake manifold vacuum is high.  The high vacuum overcomes the spring pressure and moves the valve to the low speed operation position (Fig. 10).  With the valve in this low-flow position he ventilating air passes between the valve (jiggle pin) and the outlet port.  In this position there is minimum ventilation but it never completely seals off the air flow.

     As engine speed increases and manifold vacuum decreases, the valve spring forces the valve to the full open position (Fig 10).  This increases the flow of ventilating air."  End of explanation.  Next words on the page are the heading for the next section, "EXHAUST EMISSION CONTROL SYSTEMS".  I would go ahead and quote the GM manual, but if I can read it correctly, it says essentially the same thing.  So does the Chilton.  I quoted the Ford manual for your benefit, Ford man that you are.

Now to my fellow Y Blockers on this site.  I apologize for extending this thread to this extent, and I will have nothing further to add.  Thank you for bearing with me.

John - "The Hoosier Hurricane"

John, I believe that you are correct, nonetheless we don't need this kind of confrontation on this site and I congratulate you on your restraint..  Keep up the good work with your vehicles and good luck with the "Hurricane"'  Thanks for all your help on this site. 

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

  Here is a picture of the Ford PCV valve from a 68 Mustang/Cougar manual. If you look close you will follow the operation of it.

When engine is at idle with high vacuum the jiggle pin moves toward the right when vacuum has overcome the spring and closes down the flow past the jiggle pin where marked "to intake manifold" on top picture, you will notice the spring is more collapsed in this condition and the rear of the jiggle pin is more open.

When engine is in high speed operation/low vacuum the jiggle pin is more toward the left with a greater opening on the "to intake manifold end", however the "from crankcase end" is more closed and restricting the flow caused by the spring. Notice the flat end on the jiggle pin by the dual arrow at the "from crankcase or rocker cover" end. Air flow does not pass through the jiggle pin. It passes around it as the jiggle pin is a solid piece with no through hole.

If in a backfire or blowback condition the jiggle pin will more toward the left (ie) pressure has come from "to the intake manifold" end forcing the jiggle pin towards the left and closing off the orifice hole to the "from crankcase or rocker cover" end by the flat end of the jiggle pin.

marv