jlturpin

What is acceptabe for crankcase pressure and how can I measure?

I will try to explain my symptoms, may be normal.

With Oil filler cap removed, there a light puffs of air, not enough for my snapon gauge (rigged to fit over cap) to read either vaccum or positive pressure, but if you put paper towel or something similar over it, it pushes it up (flaps in the air) I have a leakdown gauge, but have not gone through that procedure yet. Under boost, the car leaks oil at the oil seperator seals on the block. If I go through the expense of replacing the seals, I would rather pull the engine and do a rebuild.

Right now, I am starting to look for a deccent used long block or entire parts car so that I can have fresh engine and just do a swap out once the build is complete. The car still runs strong and idles well, the oil leak drives me crazy.
If I run the car with a vented oil cap (home made), the oil leak is much less from the seperator. I have drilled a 1 1/4 inch whole in the oil cap and made a filter. Yes I know the car is designed to have a sealed system, but it works for now .

Jonathan

Ski

J, you sure it's the AOS seals and not the back wafer on the balance shaft cover? Do your compression test and leakdown, that will help you check on blow by. Have you checked that old hose on top of the AOS also, they get old and swell almost shut inside from the years of oil vapor, which would prevent pressure from returning to your MAF.

jlturpin

It's not the top balance shaft seal. I replaced it, and it is dry. The turbo is dry and I have replace the Oil pan gasket, I am pretty sure that it is the bottom AOS seal. The elbow at the top of the AOS is hard, and probably could stand to be replaced. I will run the compression test some time in the next week or so. I have also considered running a catch system, like the one Lindsey sells, any comments on this would be appriciated.

Ski

Yeah, those 2 o-rings on the AOS get dry and brittle over the years. On the top hose, you can get some brake booster hose and run a complete new line...but if that o-ring is cracked not much to do until you replace it.

z3bra

For the two AOS oil rings, they're 20 mm ID by 5 mm section thickness and 24 mm ID by 5 mm section thickness. Check with some hydraulic shops and find out who sells seals and o-rings in the area. You might not be able to find the exact metric ones but there are in both cases a "dash" size o-ring that works as an acceptible alternative and those are often readily available. Or you can order them as Porsche parts from the dealer or wherever you get parts from and wait for them to come in.

Same thing with the oil ring on the bottom of the turbo, there's a dash size that isn't an exact match for it but since it's a static seal it doesn't have to be perfect to work just fine in that application. Instead of it being a 10 dollar o-ring that usually has to be ordered in, they run about $1.00. Just make sure you get one made of Viton and not nitrile rubber as nitrile can't handle the temperature in that spot and won't last more than about 15 minutes.

If you need a temporary fix and it's the hose itself that's cracked, go to a boat store and get some teak deck caulking that's either polysulfide or polyurethane based and slop some on there over the cracks. Once that stuff cures it's pretty much everything proof as far as oils and fuels are concerned. They're about 6 bucks for a tube but work better than RTV does. I used that stuff to seal a small tear in my J-boot a year ago and it's still holding up great. (I was concerned about the stuff coming off and getting sucked into the turbo so RTV was out of the question as it doesn't stick to stuff well enough that I'd trust it to stay put). If you have access to it, use aircraft type Pro-seal fuel tank sealant. It's just a better catalyzed curing version of the teak deck sealant but it's too expensive to buy some for a quick fix that size.