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Photo of Mance's Crank-Case Vent (CCV) Settling Chamber Stand-Pipe mod (horizontal alloy tube installed in vent passage near top of vent / settling chamber after bezel and screen removal):
See also the Audi TSB regarding the small amount of air pressure required to induce leaks at seals <i>elsewhere</i> on the engine. Apparently "Audi's recent TSB (C15-04-02 dated August 31st, 2004 and titled Diagnosing Oil Leakage from Gaskets) would lead one to conclude that the "problem" threshold is around 0.43 PSI." (from article in the tech section, here: https://www.audiworld.com/tech/eng116.shtml)
That is not a lot of pressure. One can imagine how any even partial blockage of the Crank-Case Vent System would exacerbate oil exiting the engine.
If you don't have an extra set of cam-covers (C/C) and/or don't want to do without your car while you do this, you can break it down into stages to shorten your down-time.
Step 1.) Remove covers, clean & replace with new gaskets as required.
Concentrate on flushing out the screened vent chamber. This is a required regular periodic maintenance procedure that should be on your list already. If you've read all the above, you will understand that if these screens become clogged, you will have exacerbated leaks elsewhere.
If your gaskets are not soft and pliable, like new ones that come folded in a little box, they may not seal if re-used. Your (multi-year?) old ones, if you've never done these before, may crack and/or break during this work. You can pre-judge your gasket age/condition prior to removal by assessing it directly at the base of your C/Cs where it wraps up around the lower edge.
I have the use of this superb parts washer which was quite helpful cleaning the pieces, you may not be so lucky:
Failing access to the above or something similar, this first step will be very messy and take some time. However, the more frequently it is done, the easier it gets. One can see how having an extra set of covers, also nets you an extra set of mesh assemblies; that can be cleaned in advance.
Step 2.) Replace rivets with machine screws.
You can see pilot345's photo here, and read the discussion:
This is where the modifications really begin. Performing this step will allow you to in future remove the OEM chamber filter mesh for cleaning, which dramatically shortens the time required. Standard disclaimers apply.
Remove the steel chamber bezel as follows:
- C/C is held upside-down gently between some scrap wood in a bench-vice;
- Scribe, centre-punch & pilot-drill out the just the rivet tops; I spent the most time of this stage here making sure I'm as on centre as possible before starting to pilot-drill. I drill down just deep enough so that my centre won't get lost when I take the rivet-tops off with the larger (larger than the rivet shank diameter, under it's squashed head) drill required;
- Remove the rivet-tops with a larger diameter drill; This drill should have a diameter > 6 mm. Don't drill through the steel bezel, just almost down to it's top surface. Just before that, the rivet heads will come off;
- Ensure you are happy with being on-centre now that the rivet holes in the bezel are exposed and adjust if required, as you may then continue to drill a pilot-hole, see drill depth marking notes below.
Once you have your pilot-holes to full depth, remove the bezels and screens. This will help prevent contaminating the screens with drill swarf. Set aside the bezels, some folks treat the stainless screen mesh assemblies with Easy-Off.
The chamber wall's four integral stand-off posts (which contain the rivet holes) where taller than the surrounding wall elsewhere, so I filed those down to the same height as the rest of the wall to prevent vapour shot-circuiting the mesh.
Final drilling to allow tapping can be done. New fasteners used will be:
Qty. 8 (4 req'd per C/C) M6 x 12 mm stainless button-head cap-screws.
Ensure your tap matches the pitch of your fasteners. I did not use a bottoming tap, just a regular one. I only drilled far enough that the hole depth barely exceeded the installed bolt depth. So some threads at the bottom of the hole where not fully formed. This did not appear to be a problem and may aid in fastener locking.
Change drill diameter to 5mm. This will leave enough material to thread into. Mark drill depth on clean drills using electrical or masking tape. Continue to drill-out the rivet shaft below the level of the steel bezel to the depth required to perform tapping. Note that their isn't a lot of extra material depth-wise to drill into as some of the outside corners of the C/C have been abbreviated, measure twice, drill once;
- Tap the holes;
Cleaned, the re-assembly can now be done with some blue Loctite.
Step 3.) Prep for & making of stand-pipes.
The stand-pipes will be inserted into the OEM vent locations and extend back into the chamber. For material, I used aluminum ski-pole tubes, they are thin-walled, cheap and easily obtainable used, and come in pairs. They are gently tapered which allows me to force-fit them exactly into the existing location, and it gives me a larger opening inside the settling chamber (the empty cavity "above" the OEM mesh) which will help reduce the "face velocity" right where the vapour transitions into the exit tube; from the chamber. This reduced velocity of the larger than OEM opening will (in addition to the stand-pipe itself) help reduce the volume of oil carried out because we have reduced the airflow's ability to carry oil/particles by slowing the air right at this point, the opening "face" of the exit tube.
X-country (Nordic) poles proved to have a more desirable thinner gauge wall than Alpine poles, but either will suffice. Beat up or bent, it doesn't matter as long as they are not cracked in the area you need, you can also carefully straighten a mild bend sufficiently. The part you will use is closer to (but still above) the basket than the grip and not more than approx. three inches long.
The maximum length of tubing that can be inserted into the chamber exit hole is just slightly less than the chambers width. Installed, I wanted the tube to extend back across the chamber as far as practical to gain as much diameter as possible. However, I don't want the mouth of the stand-pipe to be closer than about it's diameter to the chamber wall it faces. Juggling these requirements requires some measuring of diameters and lengths before you commit. As I want the largest exit opening diameter possible, I cut them too long to begin with, then carefully filed them shorter to fit. When installed, they slip into the enlarged OEM vent openings from each chamber, about one (extension's bigger end) diameter's worth.
Before I cut any tubing, I changed the bore size of the OEM chamber vent tube. Lovely pressure casting that it is, it's not perfect. It is somewhat coke-bottle shaped along it's interior length (up beyond the receiver for the quick-connect) and I wanted to remove this to reduce puddling inside the tube.
There were also small OEM casting ridges just at the junction where the chamber and exit hole meet, providing a stalactite in each C/C for oil to hang off of, and be made aerosol; right by the exit!
I removed both of these features with a very large and long round, barrel-shaped hand-file. This also enlarged the exit hole right at the chamber wall which then also allows a more desirable larger tube O.D. to be installed. Incorporating these changes where the most time consuming part of this stage. After I was happy with the casting, I polished the OEM vent tube interior with Scotch-brite and the die-grinder.
The ski-pole tubing is seam welded tubing. This weld protrudes inside the tubes. I removed the excess with emery paper on a piece of slotted rod spun with a die-grinder followed by Scotch-brite. I also radius-ed the entry-end ID of my tube-ends slightly, yes, into velocity stacks. This can be done in two different ways, either simple internal shaping by removing material and leaving the tubing OD unchanged; or true flaring. The former is easy and safe. Flaring would be more risky. This is tempered tubing so unless annealed, it will easily crack. Further discussed at Stage 5.) below.
Step 4.) Polish vent chamber walls and bezel.
This was the most time consuming stage. All casting irregularities have been removed and the entire settling-chamber (domed area above the mesh screens) now has a mirror finish on all six walls.
The bezel was hand-filed with a flat file and sanded with emery paper to break all edges; and round and polish all edges and surfaces. This plain steel piece will rust, so by not giving moisture any place to cling to, that proclivity is reduced.
After that work on the bezel, it was installed in the C/C without the mesh, and tested for leakage between the lip of the chamber walls, and itself. I then bent the bezel slightly such that the four sections between the fasteners are all pressed down firmly onto the wall's top edge when installed to further help preclude vapour short-circuiting the mesh.
Step 5.) Avoiding the 'Vena Contracta'.
The slightly enlarged bell-mouth entry I made on the stand-pipe gives it an effective face diameter that is greater than it's square-cut end would otherwise have, further reducing the airflow's entry velocity and hence it's oil carrying capability. See drawing below. "Hood" is in this case a term referring to an enclosure used to capture air efficiently.
I glued the stacks or stand-pipes in with sensor-safe RTV.
Observations and Conclusion:
Careful readers may note that, as I am still using the OEM black plastic Noise-Damper, that the most restrictive part of my CCV system may be the small openings to the Intake Tract from that piece. Nevertheless, oil consumption is now reduced dramatically, and for very low cost. Servicing will be easier and it's required frequency, just as the EGR Passage Polish Procedure has provided, I expect will also be similarly reduced. Upon dis-assembly, particles that would previously be have been taken out of the chamber are stuck to, but easily removed from, the . Oil and sludge that clings to the original velvety OEM finish inside the untouched remainder of the C/Cs, are now conspicuously absent from the polished chamber walls of the vent / settling chamber itself, the hoses, throttle-body and intake manifold interiors. Enjoy!
Last edited by Lago Blue; 06-18-2023 at 02:09 PM.
Reason: clarity
10-05-2010, 12:40 PM
Cam Cover Vents Stand-Pipe (ski-pole) Mod...
