Blown CIS Airbox? - Popoff Valve Was Epoxied Shut!!!
 

My car which is in the body shop being repainted hadn't been started in several months (I know, I know I should have gone over and done it - my bad) I started it to put it on a trailer to take it to have the headliner done and it backfired pretty hard twice in succession.

Turns out it has a pop off valve but the damned thing was epoxied shut somewhere along the line!:mad:

Now, the back pressure blew through the thing and either popped off or cracked one of the rubber oil lines - big pool of a couple quarts emptied right rear(no external oil cooler on the car...yet). The air box is not obviously cracked per se, but those little screws inside the air box around where the pop-off valve is installed toward the drivers side of the car? At least two of them have been backed (or blown!) out a quarter of an inch. On the outside of the box also toward the driver's side there are external screws that appear to have held the middle part of the box (below the top that holds the filter) to a base below - those are blown loose too. Is this thing trashed? I am assuming it is. If a pop-off valve goes bad - won't seat properly or hold vacuum - what is the fix? Can it be fixed/replaced without tossing the whole air box? I am buying a used air box from a fellow Pelican (thanks) just in case cause this thing ain't right even if it isn't truly blown. All advice appreciated. - Dan

Check to see if the rubber o-ring is still in good shape.. If it is crack or lost some of it elasticity replace the o-ring. The o-ring is one of the major source of vacuum leaks in a pop off valve upgrade.

ruf,
You can't even see the O-ring! It is all covered with dry epoxy goo. I will try to take a picture of it tomorrow and post it.

PO probably epoxied the popoff valve shut because of vacuum leaks. Popoff valve is most likely trashed.

If you are going to take off the airbox, I would suggest that you install a new airbox instead of reusing the old box. From your description of the old airbox it sound like it is trashed.

It takes about a day to remove and replace an airbox if you have never done it before. Can be replace without a partial or full engine drop.

I second, what Ruf says. It is worth buying a new airbox.

Yeah, I pretty much have deduced that. I am talking with a couple of Pelican guys right now.

Someone mentioned that most, but not all years will fit my '76 - anyone know for certain which years fit and which don't? HOw to tell the difference when one is presented to me?

ruf-porsche, Tell me more about swapping out the airbox without an engine drop.

Just spoke to my wrench and he says he can't do it without dropping the engine and that's 10 hrs charge. His rates are prettty low, but still, this is going to cost me! Of course there is all the "while-I-am-in-there" stuff that will come up if I drop the engine. Not the least of which is that I just had the entire car repainted and would want to degrease, sand, paint the engine compartment, etc. Adds up fast.

So, how to change the airbox w/o engine drop, tell me more please.

It is possible to remove the CIS without taking the engine out, but I doubt it would save a professional shop labor.
Just getting to everything without at least a partial drop would be a PITA and make everything take twice as long.
Trying to remove the intake runner nuts with the engine on a stand is a pain, I would really hate to try it with the engine still in the car.


That 10 hours is for remove and re-install right? If so that is probably
fair for book labor.
If they wanted to charge 10 hours just to remove it and another 10 to install it I would tell them to jump in a lake.
I can have the engine out of my SC in 3 hours and I don't have a fancy lift or anything.

I would expect them to do it with a partial drop which takes about 1/2 hour each way anywho.

Hey Dan ..
One of my routine maintenance in my 911 is to lobricate the POP -off O ring for that particula reason. To avoid seal dry out

VicSmileWavy

Sammyg2, thanks for the fast response. The 10 hrs is for drop and replace. He suggest a number of minor fixes while in there- depending on what we find of course. I know the valve were adjusted and cover gaskets replaces just before I bought it. He recommended some sort of seal change out relative to the fuel injection system (sorry to be so lame), but again the fuel injection system was thoroughly redone before I bought it. The fuel AND electrical distributors were changed. I think the fuel one was a rebuilt unit. Full tuneup, shielded spark plug wires installed and a number of minor leaks addressed. But they didn't do an engine drop when they did all that so I imagine there are a number of "while-I-am-in-theres" remaining. Any strong suggestions on what I should have done considering the things I mentioned that have been done already?

Vic, What do you lube the O ring with? Why doesn't that make it sticky? How often, when you change air filters?

Vash, Thanks very much. Would have called you sooner but a couple of guys PM's me with offers and I am waiting on some emailed pictures and a price quote right now. I may be calling you if those don't work out.

ATTENTION: Idiot Admission Coming: I didn't have a PPI done because the car had just had $3400 of work done, I had the receipt complete with cylinder pressures, and the PO - of very short duration - was a family member. Stupid I know. I can't imagine the shop that did all the work didn't see the POV when they changed the air filter, just not possible. I think THEY epoxied the damned thing, but why - well, obviously it leaked, but? They could have charged plenty to have it swapped out. Oh well, what's done is done, my bad, gotta pay. I see this turning into a $1000 bill very quickly with "W-I-A-I-T's" - While-I-am-In-There's.

One great thing about the 911 is that you can drop the engine at the rear motor mounts about 4-5 inches without disconnecting everything. This should provide enough access to get the airbox swapped.

Dan
With engine shot, open the POP off valve and lubricate with 30W motor oil , just a bit with your finger. This small amount of oil will avoid cracking and will help in the sealing.
No bg science. you can lubricate avery month or so when performing preventive maintenance inspections.


VicSmileWavy

Thanks Vic,
Think I have a replacement airbox lined up a nd it already has a POV. How to tell if it is working properly? I assume just operate it manually and if it resists moderate finger pressure and appears to seat fully all around that is it? I will lube it a little but otherwise it looks like a swap is a relatively straight forward R&R job, yes?

Any more help with While I am In There's?

cis
 

Hi Dan, I would suggest changing the oil pressure (idiot light) switch. Also might want to change the cold start valve that lives way back in there (unless it is new). With your car backfiring on start up, it could be that your CIS is way out of adjustment. Also do you know that the WUR is good?

good luck.

Well, I have owned this car 7 months and have driven it once. It was already in the paint shop when I bought it...or I would have addressed all the mechanical issues BEFORE I would have addressed the cosmetic ones. But, I do know definitively that the work done on it was at a reputable shop (though a little pricey!) and it ran awesome. Shifted as well as any 915 box I've ever driven. It started fine and that was after having sat for about a month when I bought it.

I know an engine drop was not done but some leaks were addressed. You guys know more about what could/could not have been fixed w/o dropping the engine. I will make a note of your advice and take a look along with my mechanic when the engine is dropped. I am a clean nut and will want to address any leaks found, I just don't want to miss easy out-of-car fixes that can't be done once the engine is back in.

Patience and someone with small fingers.

If you don't have a good set of sockets and universal, now is the time to buy it.

I took off the airbox on my 74 911 to install a popoff valve and to replace the oil pressure sending unit.

It's a little tight in there, but it can be done.

If you are buying a new airbox or a used airbox make sure you get the later box. The later airbox was redesign so there is less of a chance for it to backfire.

Hardest part was lining up all the intake runners with the airbox.

Later being what year?

Dan

My best advise is that you take your 911's engine down and perform an air tight restoration . With this I mean new runners rubbers to CIS Box /Injectors Orings etc. etc. CIS is very tricky to set and air leack are a mayor pain, and if you have so many backfires in your engiene the best thing you can do to properly adjust your car is to have a CIS seal then adjust your car timming etc. etc. Your CIS is either too rich or lean.

VicSmileWavy