engine and drivetrain Crankcase Ventilation Weber 32/36

[glemon]

I rebuilt my carburetor last weekend, all seemed to go well and the car runs fine (it ran fine before but poor MPG, have not driven enough to see if the new bits in the carb will make a difference) however, I did notice the tube running from the valve cover to the carb, it sucks up a lot of oil, and the inside of the carb was a mess, I cleaned it up, but it will no doubt be a mess again in short order, the tube runs a couple inches out from the valve cover, then there is a splice in it, I wondered if there was some kind of valve, but it is just a tube/splice in the line, should there be some kind of PCV valve? although I am thinking it would still allow flow out, so wouldn't really help with the oil situation, right?

[Mike Self]

2002s didn't have PCV valves, just that hose that ran into the original air cleaner.  When an M10 gets tired, a lot of oil finds its way through that tube into the carb, creating the mess you just found.  You can either run a longer tube down to the lower part of the engine and let the oil mist vent into the atmosphere (non PC version) or make a catch tank (lotsa threads on this) from anything from a plastic water bottle to a nice, purpose made spun aluminum tank.  The oil will collect in the tank (instead of in your carb), which you empty periodically and you can feel nice and green for doing this.  

 

cheers

mike

[peterschop]

+1 on what Mike said. Get the crankcase breather out of the carburetor. When you "rebuilt" your carburetor, did you replace the power valve above the float? A bad power valve will cause an over rich mixture and poor gas mileage but your car will still run OK because you are getting plenty of fuel. A lot of rebuild kits do not come with the power valve.

[glemon]

Yes I did put a new power valve in, I did have to order it separately, and it looked like the rubber diaphragm on the old one was pretty shot, I think it was your reply on another topic that clued me in on the power valve replacement.  I don't know the history of my motor, but it is a bit tired and blows a little blue smoke when warmed up.

[paulram]

Here is the thread I posted on the catch can.

 

http://www.bmw2002faq.com/topic/142936-valve-cover-breather/

 

I have it installed (actually ziptied) to the washer reservoir bracket until I sort out some stuff. It gets rid of the oily mist and a little on smell.  Since all my seals are shot, I won't know how much smell I can eliminate when I replace the hood seals, side seals and those elephant trunk drains.  I'm hoping alot.

 

There are a lot of cheap options.  I bought this one for the industrial look of it.

 

Paul

[glemon]

Here is what I came up with, has a clear tube on the side so you can check the oil fill level, and a drain nut on the bottom as well.  I plumbed it to the carb so should get some positive crankcase ventilation, hopefully without the oily mess in my carb,  I will add that the color of the catch can doesn't match the color of the car near as well as it looks in the pic, and in fact is listed as gold, while my car is decidedly orange.  Less than $20 shipped from Ebay.

 

Edited July 30, 2014 by glemon

[glemon]

Nice as the catch can looked, I don't think my car liked the smaller hoses used with it. The car seemed to be smoking a lot more after the install so I did some shade tree mechanic diagnostics, pulled the valve cover cap with the car idling. Holy CFM Batman! I was lucky I had the garage door open or I think I would have blown the windows out.

Anyway there was no way the smaller hose was handling any significant portion of the blowby. I went back to the 1/2" hose to the carb, but long term an engine rebuild is going to have to be put on the to do list if I keep the car.

[AceAndrew]

The M10 has a decent amount of pressure in the head even in the best circumstances.  On any decent race car you'll notice a significant amount of breathing.

 

[M3M3]

pulled the valve cover cap with the car idling. Holy CFM Batman! I was lucky I had the garage door open or I think I would have blown the windows out.

 

that much pressure at idle seems a bit excessive.  what is the health of the engine?  compression check?

 

i run 1/2in hose from valve cover to catch can.  no issues (s14). 

[Simeon]

Pressure or just smoke?  If you put your hand over the oil filler to seal the hole, does this actually build pressure or is it just a 'fluttering' against your hand?

[Mike_R]

Easy way out just get a nice catch can with a vent & drain.

[glemon]

that much pressure at idle seems a bit excessive.  what is the health of the engine?  compression check?

 

i run 1/2in hose from valve cover to catch can.  no issues (s14). 

To add to my description of the pressure at idle, I removed the oil filler cap, and a puff puff puff hit me in the face pretty hard, held my hand about 18 inches away and was quite a gush of air, not just like you could sort of feel it, but it was expelling pretty fast and hard.

 

As I have acknowledged above and in other threads, the engine is tired and due for a rebuild (although it runs really well) I should have written down the compression numbers from a month or so ago, it was either all around 120 or 130 psi for all but number three which was about 25 pounds less.  Has a knock that goes away when warm, think it might be piston slap, blows a little oil leaks a little oil, I started out wanting to keep the oil out of the carb, but thought a catch can between engine and carb might make more sense than a catch can vented to the air, etc. as documented above, realize it is all a bit of a band-aid for a tired engine that will get rebuilt eventually, although since it still runs well urgency to rebuild is not extreme.