Pop off valve on SC

My 80 SC has a pop off valve modification which came unglued last weekend. I got some glue and reinstalled it....but I think it might be backwards. The car sucks air and runs terrible. I know it has something to do with the way I installed this thing.

Question: Which way does the pop off valve go in? Should the spring side be to the right or to the left? Right now it is on the left.

Thanks!

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Donald Weintraub
1980 Porsche Red 911SC Coupe

On mine, the hinge is towards the rear bumper. That way the flap can open without hitting the filter. However, I doubt the position of the hinge has anything to do with the leak. Is the soft gasket still on?

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Graham Archer
83 911SC Cab

What is the soft gasket? Maybe that is my problem. I am not sure if I had one before....but it never ran this bad before. Can I buy it separate?

Every one I have ever seen features the spring to the back bumper, so the valve opens toward the front.

There is a rubber O ring seal. You might be able to find this at a plumbing store or a decent auto store that maintains separate bins with O rings in them (as opposed to the generic "O-ring Pak" you see at some cheapie auto stores).

Remember to seal the ends of the pin that goes through the top/bottom/spring. Use a bit of windshield seal or similar gunk that sets up semi-solid.

Peter Zimmerman, in "The Used Porsche Story" says that these cause more problems than they solve. I am not so sure of this, but he does make the point that bad-running cars can be traced to a bad seal at the POvalve. He points out the extreme case where the mix becomes lean and burns valves. A bit much maybe but it pays to pay attention to this little beauty.

Jw

OK,,,I just called Zims and the parts guy was real helpful. He said there is no soft gasket and that the valve gets installed plastic to plastic. The only gasket is the one that seals when the flap is down. I used superglue for plastic which he says will not work as well or seal as well.

I wonder if this valve has anything to do with my power loss problems???? Maybe it was never really in there correctly and it has been sucking air. Could that be?

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Donald Weintraub
1980 Porsche Red 911SC Coupe

I used a two-part epoxy (any hardware store will have it) to glue the valve to the box. I used so much that there is a nice bead of it all around the junction between the outside of the valve and the ribbed surface of the box. The gasket I mentioned (I guess you could call it an o-ring) forms the seal between the flap and the valve body.

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Graham Archer
83 911SC Cab

use a mirror to see if the epoxy is sealing all around the popoff valve. common problem, where the glue dries and leaves an air hole. if that looks ok, check the seam around the airbox. you might have blown it when the popoff popped off. any screws that are out or halfway out are a clue. they don't come out unless the box has seperated.

I will check when I get home tonight. Question: Why would the box separate? Isn't that what the pop off valve is supposed to prevent?

Don: sorry for the confusion; the only gasket is the one between the 'lid and the bottom half of the PO valve: there is no gasket between the airbox and the PO valve.

And yes, it is possible that your PO valve has been robbing you of high end performance.

Jw

An older SC owner I ran into recommended against the update. In addition to the problem that Don has run into (which is rare), he said that it removes part of the incentive for getting your valves adjusted promptly (worrying about the air box). Do people with the pop-off valve find themselves living with the backfiring and poor starting a bit longer than normal?

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Emanuel Brown
1983 911 SC Targa
http://home.att.net/~epbrown01/91183.jpg

It isn't just bad valve adjustment that leads to backfiring. A rapid change in temperature/environment can cause it, also, or so I read. The fact is, when Spring came to Arkansas this year, I had a backfire one semi-cold morning,and heard the pop off valve do its work.

The PO told me not to put it on, as it would cause a lot of trouble. Aside from saving my airbox, I haven't noticed anything...no whistles or gasps or bad running. but I was careful to use a lot of epoxy.

He also cautioned me to skip the tensioner update. Those are going in this week-end or the next.

I suggest you find a epoxy with a high heat rating.I forget what I used but it was a two part epoxy not, JB Weld ! JB Weld is handy for some things just not pop-off valves.The guys at Zims are helpful ! I've called them many times.Be sure to clean off all the super glue from the valve and airbox.

an airbox has a way better chance of surviving an explosion with the pop off valve, but occasionally they do seperate in spite of it. i've replaced several that still had the valve nicely glued in. any airbox can blow any time. i had one blow on the rack just reaching in the window and turning the key. no throttle at all.

Thanks John for the info. I checked mine last night and it did not blow. Good news for me I guess. I just need to reinstall my pop off valve and hope it does leak.