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[polilara]

Hello, I have two cam cover gasgets, one original and one Topran but no O-Rings. Does anyone know size of them to buy them separately, also size info of breather O-rings is welcome, is it nbr or Viton material you recommend?

[Enceladus]

The GM part number for the O-ring is 90411826. I believe they are ID10mm x 2mm = OD14mm. Autodoc suggests the aftermarket versions are Polyacrylate (ACM).

That O-ring, I suspect, is the same as used on the later 4 pots and these were still current post the Omega, so there are more of those engines still around. Hence the O-rings might still be available/orderable from an Opel dealer.

The problem is that the O-rings and the seals eventually go hard and squished. And then don't seal anymore. Blocked breathers then cause oil leaks. It's hit and miss as to how long third party seals and O-rings will last. I'd use a Victor Reinz kit in preference to your Topran.

The so called Tophat seal 90467543 for the breather bridge to plenum is no longer available. Clean very carefully and reuse.

[polilara]

Thanks Enceladus for reply and tips, quite strange breather construction, who designs such small  diameter piping for that important task.

[Enceladus]

It's to do with meeting emissions standards. Most cars of the period will have similar arrangements.

One of the small diameter pipes connects the purge valve, for the carbon cannister that traps fuel vapour from the tank, to before the throttle body butterfly valves. That reduces unburnt hydrocarbons.
The other one connects the small spigot on the breather box at the back of the engine to before the throttle butterfly valves. That's burning oil vapour so also reduces HCs. Probably under engine conditions where the two bigger pipes on the Y aren't effective.

[Doctor Gollum]

It's to do with meeting emissions standards. Most cars of the period will have similar arrangements.

One of the small diameter pipes connects the purge valve, for the carbon cannister that traps fuel vapour from the tank, to before the throttle body butterfly valves. That reduces unburnt hydrocarbons.
The other one connects the small spigot on the breather box at the back of the engine to before the throttle butterfly valves. That's burning oil vapour so also reduces HCs. Probably under engine conditions where the two bigger pipes on the Y aren't effective.

Correction.. for 2.6/3.2 and possibly long plenum 3.0:

The outer two pipes, 1/2", are the primary connection to the breather box as a Y tube. This feeds directly to the front of the TB.

The smaller of the centre two, 1/4", is the smaller connection on the breather box. This is the small hole into the plenum from the breather bridge.

The remaining hose, 3/8", is the connection to the purge valve/charcoal filter/evap cannister gubbins. This is the larger of the two holes into the plenum from the breather bridge.

The top hat seal not only seals the breather bridge to the plenum, but also separates the purge valve side from the breather box which prevents a vacuum leak to the intake from the fuel tank.

[Migv6 le Frog Fan]

I wonder if leaving the small pipe to the breather box disconnected would have much effect on anything ?
Also, what arrangement does the V6 Vectra have, bearing in mind its metal cam covers. A different one presumably or blown crank seals would be a common issue ?

[Doctor Gollum]

The Vectra has a different plenum design so presumably a different arrangement, possibly similar to the four pot set up