adrian1

You have a point there.

Techno Duck

First i just want to say sorry to OddJob for his thread being blown up and turned into a catch can discussion. But the purpose of a recirculating catch can plugged back into the intake system before the turbo is to maintain a vacuum on the crankcase as it was intended from Porsche and condense whatever water and oil is entrained in the vapor. The oil and water stays in the catch can, thus no end result in lower octane fuel.

The debate between recirculating catch cans and breather cans has been debated heavily and whenever the search function returns it is some reasonably interesting reading... you just need to wade through some of the non technical babble.

Oddjob, can you isolate which line the oil is coming from to fill up the cycling valve? I would assume its either the line connected to the j-boot (which i feel is unlikely) or the line attached to the intercooler pipe. And i cant remember, but does the vacuum nipple under the throttle body connect before or after the throttle plate?

Also does the compressor of the turbo look like its coated in oil? I highly doubt its possible to suck enough oil through the turbo from the AOS line unless your rings are completley shot. If you are, the compressor will probably have a very obvious film of oil on it.

Van

When was the last time a head job was done... I'd be suspicious of valve guides are valve seals.

Oddjob

Ive had a couple heads on the motor, both fresh.

Current motor has approx 2500 miles on a rebuild and had less than 2% leakdown when I checked it about 1000 miles ago.

951and944S

Yep...., I get excessive oil on an '87 street car thay I DE.

Car has SFR MAF kit and on the stainless turbo inlet pipe where the cone filter attaches, is a 90 deg elbow where the recirculating valve is positioned.

If I removed the valve itself, I can see oil in the bottom where the 90 deg turn goes horizontal.

Engine pulls strong vacuum at idle (20 in. +) and has good compression and leak down #'s.

Same issue with two different turbos.

Head was last worked about 8 years ago and is due for a preventative HG anyway but I'm betting on the guides being shot.

All of a sudden though, I'm getting max 10 psi boost and suspected the waste gate (Tial 38mm) diaphragm......didn't even think that it may be full of oil.

I'm going to check my canister vacuum valve in a minute and report back here.

T

951and944S

Jim, unless you witnessed the guides being changed, some shops will just leave the old ones or shuffle the valves before grinding for the best overall fit barely under max allowable side clearance check.

Also, the part # for the guides will net you a 1st over as I have run into this several times so if you supplied them to a head guy, they think they are the wrong ones.

I'll holler back in an hour or two about the oil in the valve but let me ask you......has the oil in your Lindsey WG caused a boost limit problem like I described above...?

Car is tracked about 6 weekends a year and street driven every day.

T

carreracoupe997

Oddjob, please tell me how you are venting the crankcase?

Techno-Duck, the vacuum nipple under the throttle body connects before the T plate.

adrian1

Jon your absolutely right about the thread though

951and944S

Jim, no oil in my plastic diaphragm, I even shined a light from behind it to make sure.

Carrera, can you drop the catch can, the OP has already requested the thread stay on topic and stated that he took the catch can off.

T

Van

Leak down won't catch (or detect) bad valve guides or seals. If the valve still closes fully, the cylinder will make maximum compression (and have great leak down in the rings are in good shape). But, remember, when the valve is closed, the vacuum in the intake manifold (suction) can pull oil out from under the cam box via space between the valve stem and the valve guide. This can cause an excessive amount of oil in the intake system.

I just looked it up in PET... did you know that turbos have a different valve seal (951.104.195.01) than the NA cars (928.104.193.12)? Could your head guy be using the wrong ones?

Oddjob

Good points about replacing valve guides. Im fairly certain that valve guides were not replaced because both heads were in pretty good shape.

I supplied the stem seals from aftermarket (V. Reinz?) wide fire ring head gasket sets, so Im not sure that those seals match the factory part numbers. Van, are the stem seals different for all Turbos, or just Turbo S heads? I know there are different part numbers for the Turbo S valves and a slight dimensional/tolerance change for the stems.

My current thought is that bad valve guides and/or incorrect valve stem seals wont cause oil getting back up into the intake system. The motor will burn oil and smoke but little if any will be drawn back past the intake manifold and into the vacuum lines. But I will put some more thought into it.

Oddjob

My guess is that the oil to and thru the cycling valve and down to the wg is coming off the intake runner/banjo line. I have lost boost on track, running well below normal pressure - both times when it happened recently, I pulled the cycling valve and drained oil out of it. Replaced with a spare and boost was fine.

I have not filled the WG diaphram up with enough oil to cause a WG function problem, but I find it quite odd that oil is getting down there.

What are you using for boost control? Might want to check whatever valve/controller you have in line to your Tial.

Van

Hey Jim, according to PET, both the M51 and M52 engines use the same valve seals.

Why I think valve seal / guide blow-by can get into the intake: when an intake valve is closed, it's the "sucking" of another cylinder that causes the oil to come out. Again, because the valve is closed, this oil (or oil mist) has to travel up the intake runner to the central part of the intake manifold, before it can travel back down the runner to the cylinder that has a valve open and the piston on the down stroke. Because of the positive intake pressure under boost, a lot of this oil settles out as a liquid and sits around in the intake system - collecting in all sorts of places. In an intake where there's always some vacuum, the oil is more likely to get sucked into the combustion chambers and be burned. But, under boost, nooks and crannies probably "collect" the high pressure (because of a velocity slowdown and turbulent vortexes (like eddy currents in a river dropping sediment)) and allow the oil to puddle up.

I have no evidence to back this up... just my, sometimes convoluted, thought process.

Oddjob

Which version of PET do you have? I have version 6 and it shows for MY 87-88 that the only difference between an M51 head and an M52 head is the valve seals -00 vs -01 (which now superceeds the previous M51 seal). It does not identify different valve part numbers for either intake or exhaust valves, which I am nearly certain is incorrect - as the later heads definitely have different facing on the intake valve heads.

Van

I have PET 6 - but don't see the same thing you see... From '86 thru '89 (the M51 and M52 engines) all have 951.104.195.01 - I don't see the -00 p/n.

It is odd that it's listed twice (with the same p/n) - that does indicate that PET might be in error.