"Tuning" or dialing-in the pancake-style PCV valve

[Boink]

"Tuning" or dialing-in the pancake-style PCV valve

OK, I installed the old pancake-style PCV valve on my 1275 (thanks, again, Bill L.). I put in a new rubber membrane, polished the body up and it really seems to work well. In this configuration, I have a hose running from the oil seperator (on the timing cover) to the PCV pancake and then from the PCV valve straight down into the top center of the "log-style" intake manifold (using dual HS2s).

BUT, the other day, a <span style="font-weight: bold"><span style="text-decoration: underline">HUGE</span></span> amount of oil burped through the PCV valve (or I think it did) and into the manifold (producing voluminous/billowing smoke that lasted for a fair length of time). Twas embarrassing. :blush: I figure that either the valve briefly stuck <span style="text-decoration: underline">OR</span>there is too much vacuum... likely the latter.

So, my question is, how does one dial-in the correct vacuum to one of these (possibly by fooling with the tube diameter to the manifold or by installing some kind of control valve there or maybe some sort of restrictor).

Thoughts? Thanks.

 

[smaceng]

Re: "Tuning" or dialing-in the pancake-style PCV valve

That is the arrangement I have on my 1275. See below. I did not dial anything in and the no restrictors were put in the lines. I have not followed your posts, but did you rebuild your engine? It may take some time to seat the rings, which would also push the oil out the exhaust.

 

[Jim_Gruber]

Re: "Tuning" or dialing-in the pancake-style PCV valve

Sounds like a diaphram issue. With my 1098 in Bugsy without the PCV Valve there is major oil leakage out the back scroll seal. Since I put in the PCV Valve Bugsy still marks his territory with 5 oil pan bolt leaks/drops whenever I stop but cardboard is cheap and DPO glued on the oil pan and it will not come off with engine in the car. I tried many years ago and made the decision,"Dr., Do no harm!" Figured I could be in far worse shape if I pried on the oil pan and bent something. Again cardboard is cheap and I try to be nice and not park of concrete driveways.

 

[Boink]

Re: "Tuning" or dialing-in the pancake-style PCV valve

My set-up looks identical to the photo.

I leak very little oil, and I think the rings are fully bedded (though the valve-guides are only about 150 miles old - and those guides are tight). I put the pancake PCV valve in when I rebuilt the head (just a short bit ago). I don't think my crankcase pressure is high. Maybe the PCV was briefly stuck (and I'll explore that).

I'd read some posts about folks that addressed the fact that the tube to the intake manifold shouldn't exceed a certain size (and I think my narrowest point is either the output of the PCV or the threaded brass stem I put into the intake manifold - which isn't too wide).

 

[nomad]

Re: "Tuning" or dialing-in the pancake-style PCV valve

Mark, do you have the correct oil fill cap? The cap that went with the pancake PCV was vented with a filter incorporated in it. My Datsun engine originally used the typical check valve PCV with a vent from the valve cover to the air cleaner. According to what I have read the PCV has a constant suction on the crankcase but under hard acceleration the PCV is sometimes overwhelmed and when it is the engine vents thru the valve cover to the air cleaner. I havn't studied how the pancake PCV is suppose to work but if memory serves from when I've had one apart it appears that the greater the vaccume the more the valve is damped down. Seems logical to try to keep somewhat constant vaccume.

 

[nomad]

Re: "Tuning" or dialing-in the pancake-style PCV valve

What I meant to say in my long winded reply was if pcv can't handle the blow-by it is supposed to vent thru the cap or the valve cover vent. I'm betting something isn't right with your pcv though.


Kurt.

 

[Boink]

Re: "Tuning" or dialing-in the pancake-style PCV valve

What I meant to say in my long winded reply was if pcv can't handle the blow-by it is supposed to vent thru the cap or the valve cover vent. I'm betting something isn't right with your pcv though.

Kurt.

Thanks Kurt. Actually, I have the old vented rocker cover (which I was about to change out to an alloy one). The rocker has that tube that sends any alternate blow-up to the forward carb. So, maybe the valve was stuck or something.

All this never happened PRE-pancake PCV valve, and I've definitely seen oil in the valve... so I was just looking dial that vacuum back a bit (since it doesn't happen all the time).

EDIT: forgot to add that my new alloy cover has a vented cap too.

 

[Boink]

Re: "Tuning" or dialing-in the pancake-style PCV valve

Was just reading this thread: https://www.britishcarforum.com/bcforum/ubbthreads.php/topics/871634/Oil_in_PCV_valve#Post871634 and I think I'll reduce the orifice diameter (to 9/64" or less).

 

[lbcfan]

Re: "Tuning" or dialing-in the pancake-style PCV valve

It's interesting. I always thought that the connection to the forward carb air filter was to supply filtered air to the rocker cover, to be drawn down to the crankcase if needed. I hadn't thought about the reverse.

I posted on the "oil in the PCV valve" thread that I checked my vacuum upstream of the PCV valve today, and it does stay in a close range of 18 to 22" Hg at all rpm, with 20" at idle.

 

[Boink]

Re: "Tuning" or dialing-in the pancake-style PCV valve

It's interesting. I always thought that the connection to the forward carb air filter was to supply filtered air to the rocker cover, to be drawn down to the crankcase if needed. I hadn't thought about the reverse.

I posted on the "oil in the PCV valve" thread that I checked my vacuum upstream of the PCV valve today, and it does stay in a close range of 18 to 22" Hg at all rpm, with 20" at idle.

Thanks. Yes, I've been tracking that parallel thread as well. Good info, and I found the oil/air separator thing interesting.