Crankcase ventilation

[Errol62]

There has been considerable discussion about grey motor crankcase ventilation recently, specifically on Craig’s Thread:

Seagull Grey EK 2106
https://r.tapatalk.com/shareLink?share_ ... are_type=t

Rather than continue discussion on there I thought it appropriate to start a separate thread. Patrick (gpi) posted the following link to a US Chev truck forum article on retrofitting positive crankcase ventilation to what I assume to be the motors the Holden grey was derived from:

http://devestechnet.com/Home/PCVInstall

Well worth a read thanks Patrick. This covers fitting a PCV valve to the crankcase in a slightly different application, where the road draught vent tube is fitted to the engine block, rather than side plate as in the grey. This side of the equation is relatively straightforward. The article says little however about the induction side of things.

What concerns me is the effect on mixture tune when this modification is made. Notwithstanding the pcv valve controls the rate of crankcase gas induction, the carb surely needs to be rejetted to make up for the relatively lean crankcase gas being introduced. My memory of playing with these systems is that engine will lean out when the valve is pulled out of the crankcase, but when the valve is blocked off the engine will immediately stall. This indicates to me sudden and significant enriching of mixture beyond what the engine can tolerate at idle.

Anyone else interested in this? Otherwise I’ll shut up.


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[ardiesse]

Clay,

Your experiences of mucking around with PCV systems are different from mine -

If I pull the PCV valve out of the rocker cover, still attached to the hose (talking post '67 red motors here), the engine idle remains unaffected. If, then, I block the PCV valve with my thumb, I can hear the valve "clack" back to its zero-vacuum state, and the engine idle drops maybe 50 rpm. It's only if the hose is unplugged from the valve, or the inlet manifold for that matter, that the engine idles fast and lean. It's much the same effect as unplugging the brake booster hose, or for the old farts, unplugging the vacuum hose to the wipers.

Granted, a PCV valve acts like a small intake leak. But its effect is small, and can be compensated for by slowing and enriching the idle slightly. The jetting of the main discharge system does not need modification, because the quantity of air being drawn through the carburettor when the throttle is opened is way bigger than the quantity of air flowing through the PCV valve.

Rob

[Harv]

Granted, a PCV valve acts like a small intake leak. But its effect is small, and can be compensated for by slowing and enriching the idle slightly. The jetting of the main discharge system does not need modification, because the quantity of air being drawn through the carburettor when the throttle is opened is way bigger than the quantity of air flowing through the PCV valve.

Crankcase gas is a real mixture. Granted, some air but equally a gut full of blowby and oil fume. That crap is carbon-heavy, and needs a fair amount of air to burn. Methinks little effect on mixture.

Cheers,
Harv

[Dr Terry]

Adding a PCV valve to a Grey will have little or no effect on running fuel mixture (above idle speed).

We used to fit a lot of PCV valves at our workshop during the 70s. TRW & others made conversion kits for many common cars.

All that is required after fitting is a small adjustment of the idle mixture. In most cases fuel economy at city traffic speeds will improve slightly.

Take a leaf of of Holden's book. When PCV valves were added midway thru the HR series to the single carby 161 & 186 engines, no changes were made to carby jetting.

Dr Terry

[Craig Allardyce]

I'll let you know once I get around to doing. Selection of the correct PCV valve is paramount. This is where the mixture change effect will or wont occur. Pick the valve with the wrong spring tension or flow rate that isn't suited to your engine and you may well have an issue.

I'm very reluctant to just go and pick an off the shelf "universal" PCV valve. Some testing will be in order with my O2 sensor.

[Errol62]

Thanks for straightening me out folks. I relied on 40 year old memories. It seems like a pretty good solution to clean up the old grey’s act. The standard vent location could be used, or blanked off and vent via the rocker cover a la red motor etc??


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[Craig Allardyce]

For whatever connection point you use for the valve. there still needs to be a corresponding inlet breather to allow fresh air to sweep through the crankcase and exit via the valve. Ideally the inlet should be plumbed above the throttle valve (air cleaner area) to allow reverse flow under full throttle applications where there is little to no manifold vacuum to draw fumes in the normal direction of flow. This is why later engines sealed the oil filler cap and connected another 2 way breather line to the air cleaner.

[Errol62]

That’s the system on my blue motor. Works well as long as you don’t have much blow by.


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[Patrick_R]

Gents,

I can’t see why anyone would want, or need to take their car away from the original design of the grey.

Is there something I am missing here?

Ric.

[Craig Allardyce]

Mines a daily driver and gets flogged hard. Sometimes you get sick of cleaning oil that vents from the draft tube and breather cap. That's my motivation for improvement.

[Errol62]

Now that I am looking at running X2 induction on the ute I am pondering how to vent the crankcase. I believe that although HR 161, 186 and 186S motors ran factory PCV, the HR X2s ran draft tubes as per all EH and HD. I had a draft tube that was on the 186 when I originally got the ute, but I got rid of it, and in any case I'm not a fan of them.

[Blacky]

I read somewhere not so long ago that you can buy an adjustable PCV ??? I am sure Dr Terry or Dr Allardyce would know the correct way to set it up

[Dr Terry]

The early 161 & 186 engines (pre-June 67) had no PCV either. The 186S was the first.

The best way to plumb a PCV to X2 carbies is to make 2 adapters to fit under the carbies & fit a 3/8 diameter tube to each, run these to a T-piece & then to the PCV valve.

Have a look how GM-H did it on XU1s.

Dr Terry

[Harv]

Adjustable one:

http://mewagner.com/?p=444

($$$$)

Cheers,
Harv

[ardiesse]

What Dr Terry recommends is what I did when fitting an X2 setup to a mate's EH with PCV waaay back when.
(Hint: use manifold studs in the inlet manifold, and make the tubes come out at a 45-deg angle.) It's a fair bit of messing around with getting flanges fabricated.

Rob