Pictures of airbox (lower half)

prebordao · 08-29-2012, 06:04 AM

Would like to find pictures of the lower half of the airbox (CIS) and can't seem to find any... Just curious, don't know really the flow that the air follows.
Anyone can help ?

Bob Kontak · Bob Kontak's Garage

Porsche CIS air box inspections 911 Motor Meister 2.4 2.7 3.0 - YouTube

prebordao · 08-29-2012, 07:37 AM

Thanks, very informative video.
I think many people (like me) don't realize that when a CIS airbox blows, they're usually hairline cracks, thus very easy to go unnoticed.
This came about because yesterday I noticed that one of the screws inside the airbox (near the back) was a bit loose... Maybe I'm getting close to nailing my 2-3k hesitation...

E Sully · E Sully's Garage

Early CIS airbix did not have the spider. Added later to improve cold start to prevent backfire. That first box has the pop off valve reversed. He quickly mentions it later on, air filter would prevent it from opening all the way.
Also note the small nipple on the bottom of the air box when he turns it over. At the one minute mark on the video it is by his thumbnail. This goes to a drain tube that runs down the engine by where the engine oil cooler mounts. There the tube goes into a metal cylinder with a rubber flapper valve on the end. This allows oil from the oil tank vent to drain out of the air box. The flapper valve allows oil out while preventing unfiltered air in.

prebordao · 08-29-2012, 08:20 AM

Does that nipple and drain tube also exists in a 74 ?
If that rubber flapper goes bad or missing, could be another source for air leaks.

Bob Kontak · Bob Kontak's Garage

I can't find the nipple in the parts diagrams for the years ending in 73/77/83 but I do remember an old post where a guy could not figure out where his oil leak back by the oil cooler was from and I am pretty sure it was that hose.

Bob Kontak · Bob Kontak's Garage

Preb - Can you duct tape the top of your airbox and put a little air pressure in there? If it is a cracked box it should be easy to find where it is leaking.

prebordao · 08-29-2012, 08:35 AM

Bob, I was just thinking, if it cracks in the seam shown in the vid, the only way to make sure is by removing it, or not ?
Although, with a couple of screws slightly loose, the probability is bigger.

E Sully · E Sully's Garage

Those 3 parts are difficult to find in the PET. If missing it would not be unmetered air coming in, just unfiltered. It could also drip oil onto the top of the engine instead of by the clutch and oil cooler. It could be a source of unexplained oil leakage after the triangle leaks have been resealed.
I see the drain nipple on the bottom of the later air boxes in the video, so I would think the parts were still used, or a similar type drain was installed on later models.
Leave it to Porsche to create an intentional drip so the car can mark it's spot.

prebordao · 08-29-2012, 08:45 AM

Could be the parts numbered 7 in the diagram below ?

Bob Kontak · Bob Kontak's Garage

The video says the boxes often crack on the underside where no one can see it.

Run the car at idle and spray carb cleaner onto the underside of the airbox - not sure what approach angle - to see if it sucks it into the intake and changes the RPM.

I would spend some time doing that as it will be far easier than taking the box off.

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Bob Kontak

The video says the boxes often crack on the underside where no one can see it.

Run the car at idle and spray carb cleaner onto the underside of the airbox - not sure what approach angle - to see if it sucks it into the intake and changes the RPM.

I would spend some time doing that as it will be far easier than taking the box off.

Bob,

It would not be effective spraying carb cleaner to the underside of the airbox for crack or air leak detection. Even with a blown air box (@ underside) the sprayed ether/carb cleaner would just flow down. Try it and see for yourself. That's one reason why I use pressurized gas and totally submerge the air box underwater for testing. Even the soapy water and compressed air fails to detect the micro crack at this spot (underside).

Tony

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by boyt911sc

Try it and see for yourself.

No need. I trust your experience.

You definitely have to hit the suction point dead on and it has to be big enough to allow enough to enter and change the RPM.

prebordao · 08-29-2012, 01:13 PM

Tony
How do you get rid of those tiny cracks ?

E Sully · E Sully's Garage

A few years back I had a small leak in an air box I got when I picked up a complete system for spare parts. I removed all the screws and carefuly pried open the seam with a small putty knife, and then sealed it with a glue I found in the hardware store that claimed it was fuel and heat resistent. I can't remember what it was now, but next time I'm out I will see if I can locate it.
In case your interested, here are pictures I found, first being a 74, second a 77. Seems the drains were still in use. Parts you found must be a different system.
Part 11 in the diagram is 911 108 021 02
Pelican Parts - Product Information: OEM-91110802102
Part 12 in the diagram is 253 260 180
Pelican Parts - Product Information: OEM-253260180

Bob Kontak · Bob Kontak's Garage

Cool - Thanks Ed.

dale914 · dale914's Garage

So I watched the video, saw that I'm missing the same screw. I have the rear facing pop-off valve, have heard it pop about 3 times in the past 12 years/50k miles, I've always thought that the box was fine, but does the missing screw promise that its not? Does it need to be replaced? Is this possible to do from home? It has always seemed to run fine

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by dale914

So I watched the video, saw that I'm missing the same screw. I have the rear facing pop-off valve, have heard it pop about 3 times in the past 12 years/50k miles, I've always thought that the box was fine, but does the missing screw promise that its not? Does it need to be replaced? Is this possible to do from home? It has always seemed to run fine

Dale,

If the missing screw from the airbox was displaced by a backfire, you certainly have a blown or cracked airbox. The crack might not be visible at a glance but a closer scrutiny would reveal it. Some of these tiny cracks are almost invisible during inspection unless you pressure test them.

Tony

dale914 · dale914's Garage

Thanks for the input Tony, now here's the question: the 911 seems (I think so?) to run/idle/start/accelerate just fine without any problems; does it need to be fixed or replaced? It may have been broken for 12 years/50k miles, not sure when it blew, is it bad if I keep it as is?

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by dale914

Thanks for the input Tony, now here's the question: the 911 seems (I think so?) to run/idle/start/accelerate just fine without any problems; does it need to be fixed or replaced? It may have been broken for 12 years/50k miles, not sure when it blew, is it bad if I keep it as is?

Dale,

If you are not experiencing any problem with your CIS, leave it alone. If the missing screw is bothering you, install one and enjoy driving the car. When the time comes and the engine started showing some starting or running problem related to air/vacuum leak, you know where to first look.

Tony