CIS Airbox Drain

[tiemeyj]

Hello,

I just reinstalled my engine in my '74 Targa after addressing various oil leaks. After 500 miles, no leaks to mention except for a small amount of oil from the CIS airbox drain that runs behind the oil cooler. It's not overfilled but I do get a lot of oil vapor/mist coming into the airbox from the tank when warm...probably rings but that's another project for another day.

I've always noticed part 7/4 in the PET diagram below which looks like a pipeline to redirect the airbox drain dibbles away from the engine. My car never had one but I sourced one and cannot figure out how to mount it. Does anyone know if this will work on a '74 car or where it mounts? I thought it would attach to the tin bolts that run across the back of the case, but nothing seems to line up.

I'll eventually install a oil catch can to prevent the vapor from even getting into the airbox.

Thanks

Justin

[Walter_Middie]

Justin,

This is all my 1975 has for an airbox drain tube.



You say it is not overfilled with oil - I assume you are aware that it is recommended that the oil level is only halfway up the dipstick - not up to the max. l've found that this keeps excess oil from getting into my airbox.

[fanaudical]

There is a duck-bill check valve that snaps over the big end of the piece in the picture above (item 7/2 in the diagram). That is a necessary component for the drain to work (otherwise you're just sucking unfiltered air into the drain when the engine is running).

I have the CIS airbox drain capped off on my '75 2.7. I keep the oil level half-way between the dipstick marks. I open the airbox to re-grease the pop-off valve o-ring every 3 months and take a quick wipe with a rag to remove oil residue.

[tiemeyj]

Thanks for the replies. I’m aware that the oil level should be no more than half way up the stick. I usually keep mine just below that to avoid any mess. My duckbill valve is pretty crusty and I have a new one on the way. Maybe that will help control any drips. I’ve never seen the pipeline on any car or in pics.

Thanks again

[E Sully]

My '73.5 is the same as Walter_Middie.
From looking at the PET parts 7/1 7/2 and 7/3 were used from '75 back, part 7/4 was added from '76 on.
The first photo shows a rusty 7/1 with the rubber flapper valve 7/2. In the second photo you can see the top of 7/2 and just make out the braided hose 7/3.
It was a crude way to vent the oil accumulated in the air box onto the ground by the clutch and oil cooler. Later part 7/4 seems catch the drips and drain lower and more towards the right side.



7/4

[HarryD]

My 1973.5 did not have the drain pipeway. The drain line from the air box was laying in the triangle of death. I got a small bore section of tubing and extended the drain to below the transmission.

[EC900]

My 2¢…
Did you inspect id Part #25 is intact, this connects hose from oil tank to air box. I wonder that if it’s missing, that it could cause much more neg pressure than normal causing oil vapors to be pulled into the intake.
Is #7/4 part of the air flow sensor to throttle body with #7/2 the check valve intended to restrict unmetered air (when oil cap is removed it would prevent a drop in idle speed)…and not exactly a drain for the air box?
But worn rings allow oil into the combustion chamber and out the exhaust.

[E Sully]

Part 7/2 is just a one way rubber flap valve to keep air out, and let oil drip. They fall apart after time, but I was able to buy a new one a few years back.
https://www.pelicanparts.com/search/?q=253+260+180
Part 7/4 is just a pipe to catch the dripping oil and divert it. I did a quick photo shop and pasted it where it would mount on the lower left in the picture.
It would catch the drip from the original drain and divert it over the exhaust to the outside.
HarryD describes something similar that he made. I may make something similar, doesn't look hard to fabricate.

[tiemeyj]

EC900 - Thanks for the note. Part #25 is there. You can remove the air cleaner snorkel and see the vapor streaming from the tank hose and getting sucked passed the metering plate. Pretty sure the later cars had the breather hose connected in the middle of intake boot so oil vapor would not condense and collect in the airbox. It's just a crude design for the early CIS cars.

E Sully - Thanks for the mock up. That's exactly what I had in mind, however, the crossover pipe gets in the way and prevents everything from lining up. I think the '77 and later cars do not have that pipe. Should be fairly easy to fabricate something or modify the factory piece to work. It just bugs me to have to redirect a built-in oil leak! I found a high-flow oil catch can from Mishimoto that has 25mm ports which match the ID of the tank and airbox breather hose. I think that will solve my problem and keep the airbox free of oil.

Too much time and money went into fixing leaks to just accept an engineered dribble!