Crankcase ventilation and brake servo vacuum

[Burdekin]

I would have thought it would work but maybe you also need to change the manifold nipple size.

Some pics would help.

[Burdekin]

Originally Posted by HRA

Thanks Burdekin.

I'm running my PCV in the opposite direction. Sucking from the crankcase and venting via the oil-cap. But that should work - it's how PCV was plumbed on B18 Amazons.

The other difference is that I only have one vacuum spigot on my inlet manifold. Hence the Y-piece so I can connect both servo and PCV valve.

So why does my PCV valve let so much air into the inlet manifold that there's not enough vacuum for the servo...?

I couldn't see it in the pictures, but I take it you have a PCV valve fitted between the manifold and oil-filler cap?

Don’t think there is a NRV fitted to the B20.

The B20 oil traps are different also, larger connection to the engine and has a flame guard fitted where the hose connects to.

[HRA]

Thanks again Burdekin,

That sounds like the bit of information I was missing. I need to put a restrictor in the hose between the PCV valve and my Y-piece. We've got a lathe at work so I'll see if I can make something to block one arm of the Y-piece down to a 2mm bore.

[Burdekin]

I assume you are wanting to do it all like a B18 as you are doing the negative early setup rather than the later B20 positive.

[142 Guy]

Originally Posted by HRA

Thanks again Burdekin,

That sounds like the bit of information I was missing. I need to put a restrictor in the hose between the PCV valve and my Y-piece. We've got a lathe at work so I'll see if I can make something to block one arm of the Y-piece down to a 2mm bore.

The Volvo factory B18 way to do it would be to install the Volvo nipple with the internal restriction in the intake manifold. Run a hose from the nipple to the Tee. One side of the tee branches to the brake booster and the other side branches to the top of the PCV valve which is mounted on the top of the oil seperator box.

As per that FSM Bulletin provided by Burdekin, the original nipple is part number 942461. This was superseded by part # 947043 the only difference being that the early nipple is straight and the later nipple has a hose retaining barb on it. Both parts are still available from Skandix. This arrangement requires the PCV valve # 418982.

Your method of installing a restriction in the hose section between the Tee and the top of the PCV valve should also work. This might get you a mention on the Swedish Embassy web page covering different ways to arrange the PCV system on B18s, hopefully in the working options as opposed to the 'don't go there options'.

[HRA]

Originally Posted by Burdekin

I assume you are wanting to do it all like a B18 as you are doing the negative early setup rather than the later B20 positive.

Yes, but only because neither of the oil-filler caps I have has a tube fitting.

[HRA]

Originally Posted by 142 Guy

The Volvo factory B18 way to do it would be to install the Volvo nipple with the internal restriction in the intake manifold. Run a hose from the nipple to the Tee. One side of the tee branches to the brake booster and the other side branches to the top of the PCV valve which is mounted on the top of the oil seperator box.

As per that FSM Bulletin provided by Burdekin, the original nipple is part number 942461. This was superseded by part # 947043 the only difference being that the early nipple is straight and the later nipple has a hose retaining barb on it. Both parts are still available from Skandix. This arrangement requires the PCV valve # 418982.

Your method of installing a restriction in the hose section between the Tee and the top of the PCV valve should also work. This might get you a mention on the Swedish Embassy web page covering different ways to arrange the PCV system on B18s, hopefully in the working options as opposed to the 'don't go there options'.

Thanks 142 Guy,

418982 is the PCV valve I've just fitted. I've conncected the larger spigot to the oil separator on the side of the crankcase.

I wonder how the original set-up you described every worked though. There wouldn't be much suction through the 2mm hole in the nipple on the manifold, and it would be shared with the brake booster and the PCV line. The PCV line is open to atmosphere albeit via the crankcase, head and oil-filler. Surely the brake booster wouldn't experience much vacuum at all?

I'll see how I get on with the restriction in one arm of my Y-piece. At least that way I'll be giving the booster virtually full manifold vacuum, with just a trickle of air coming through the 2mm restriction from the PCV line.

[c1800]

There might be an arrow on the PCV valve.

[HRA]

Originally Posted by c1800

There might be an arrow on the PCV valve.

That was my first thought, but sadly not. I suppose that to the designer it was obvious; it's only half a century later that it's not crystal-clear.

[Ron Kwas]

HRA;

You're mixing Vacuum and Flow...there is NO Flow to/from Brake Assist unit other than to evacuate the volume to achieve vacuum, and there is only a very limited flow from the Crankcase due to orifice limiting, and it is unidirectional because of the PCV Valve.

Suggested reading: https://www.sw-em.com/pcv_diagrams_and_notes.htm

Cheers