• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Oil in PCV valve

Share this page

L

lbcfan

Jedi Trainee
Offline
I wanted to maintain a controlled negative pressure in the 1275 crankcase. However, I have a weber DGV, not the 1275 twin carb manifold.

I took a hose from the oil trap to an original PCV valve, and from there to a 5/16 connection on one of the two carb manifold arms.

I've been running for a month or so and occasionally I would get a cloud of smoke after waiting at a light and then accelerating. Long story short I checked the PCV valve and found it full of oil.

Do the stock engines suck oil into the PCV valve? I can't figure out why my arrangement is any different.

Thanks.

Michael
 
The diaphram may need to be replaced if you are talking about the old flying saucer type. Controlled pressure through a measured orifice. Without the PCV in place Bugsy my 1098 in a '68 Sprite blows oil out the back seal like the Exxon Valdez. With PCV in place, a 5 drops when I stop. Just marking his territory.
 
Thanks Jim. It is the "flying saucer" type, and it has a brand new diaphragm. I'm glad to hear the measure is correct for minimizing the rear seal leak.

When I opened the valve it was full with oil up to the raised suction outlet. I'm thinking my occasional cloud of smoke came from a hard right or left turn after a traffic light sloshing oil into the suction port.

I've removed the valve for now- I'm concerned that the concentrated oil will hurt the cylinder break-in, not to mention the smoke is embarrassing...

The valve is not mounted adjacent to the engine, but remote, on the DGV bracket, where it might stay cool. It's possible I'm condensing the oil vapor in the saucer, but who knows. It sounds as though I'll have to connect the oil trap directly to the carb manifold so the oil cannot collect anywhere.

I welcome any suggestions.

Michael
 
Michael,

One my 1098 as well as a 1275 I have as a spare, the PCV is connected directly to the mainifold for a vacumn source not to the Carb. I don't think the Weber has a real way of providing a vacumn source. Others need to chime in as I've never messed with a Weber.
 
If I recall, there needs to be a baffle in the rocker cover to prevent oil from spraying into the PCV hose.
Some oil is normal, as it falls out of suspension, but it should be drawn into the inlet normally. I have seen the saucer type installed upside down before, and had some of that issue. But it's been decades, can't remember the exact circumstances.

Does your rocker cover have a baffle?

Dave
 
Dave- The 1275 has a cylindrical oil trap on the timing chain cover, and from there a 1/2" hose to the PCV valve. From pictures I've seen the original 1275 SU manifold had a direct connection for the PCV valve outlet. My original 948 used a draft tube to create some negative pressure in the crankcase at speed. I believe the rocker cover vent is for air intake to replace the air drawn from the crankcase.

Jim- The weber does have a vacuum connection that I use for the vacuum advance on a pertronix distributer. My connection for the PCV is to the carb manifold, not to the carb.

I don't know why my configuration would encourage more oil to collect in the valve than in the stock set-up, except for the fact mentioned before that the valve casing is not warmed by proximity to the block, possibly creating more condensation of the oil. In retrospect the saucer and raised suction port seem like a dumb design- not like the other British engineering...

I can either stop the hard right turns after stops at intersections to keep the oil from sloshing in the saucer, or get rid of the valve. I think I'll get rid of the valve.

Thanks again.

Michael
 
Mike,

I'm not sure if you missed it in my email, but I think you should try reducing the orifice to 9/64". You are probably getting too much vacuum from the manifold.
 
I agree with Gerard, I believe you have too much suction on the vent or you would not be getting oil pulled from the crankcase. Also is your valve cover vent stock or equivalent. The caractaristic's of the weber may have something to do with the problem as well.
I had a devil of a time coming up with a pcv setup on my Datsun engine Midget till I got a small enough restriction in the line. In my case I was having trouble with leaning out.

Kurt.
 
Thanks- I'll reduce the orifice, although I might have overstated the size. It's actually the size of a vacuum line. Whats puzzling is I thought the PCV valve would prevent excess flow- that's why I added it. From photos I believe the tap on the SU manifold is larger than the tap I'm using (unless there is a hidden restrictor), so the size should not be the cause.

I wonder if anyone makes an oil trap or separator that I could add to the hose before the valve, at the outlet of the timing chain cover...
 
You don't have the amount of vacuum from the carb vents that you would from the manifold. Also, depending on the location of the vacuum port over the years, a closer examination will reveal a restricted area that isn't obvious and not indicative by the size of the vent pipe.
 
Gerard-

I hadn't seen a manifold close-up. Good to know that there is a restriction. I'll bring down the size of the tap and see what happens.

Thanks once again.
 
One thing that I have done is to run a hose from the rocker cover to the timing chain separator, put a "T" in the line and hooked the 3rd part of the "T" to the PCV valve. If you do this be sure to rig it so that any oil in the hose assembly drains down into the timing chain cover and not into the PCV valve.
BillM
 
Bill-

Seems like a good idea. Too late for me though. I ordered a Jegs oil separator that I should be able to mount on the DGV cable bracket. It's pretty compact, transparent, and has a drain valve. I did a lot of searching of oil catch cans also, but not much works well in the bugeye engine compartment.

It'll be a week or so in shipping, but I'll report back after I've tried it out with the PCV valve.

Thanks to all,

Michael
 
In an effort to protect the PCV valve from oil I added a Watts oil/air separator. The link below is to a couple of photos. The engine is starting to look a little like a still, but if it works I'll be happy.

I can't find any figures for the vacuum that the PCV system should draw. I measured 20" Hg at idle, and a constant 18-22" range throughout all rpms at the inlet to the PCV valve. I do not have a controlled vented cap on the rocker cover- just an open vent. Again this is a Weber DGV carb. The orifice connected to the intake manifold is 3/32".

Does the vacuum level sound correct, or am I asking the wrong question?

Thanks.


https://photobucket.com/pcvmods
 
Now to figure out a qway to return oil automatically back to the engine. Normally the PCV Valve provides the corect vacumn level so the oil doesn't get sucked out past the timing chain cover or else if it does get pulled up it can't get up to the PCV Valve, climbing against gravity, and flows back down into the sump. At least that's how I think it's supposed to work.
 
I would agree with the concept- especially with the 1/2" hose- the air velocity should be pretty low to limit carryover.

I went this route because the clear bowl and drain will make it easy to maintain, without adding a drain back to the sump. Don't know if it works yet- drove 20 miles and no oil in the filter or the PCV valve.
 
Nice and tidy little setup Mike. Has it made an improvement?
 
Well, the filter is still clean, but so is the PCV valve. Go figure. I just have fun trying to solve apparently non-existent problems.

By the way, the re-sleeved master cylinder is working great. The clutch pedal pressure is now perfect, and it hasn't lost a drop of fluid in 500 miles. Thanks.
 
Excellent Mike! Glad to hear it!

Are you still getting some leakage from the rear seal after working out the vent situation?
 
Somewhat reduced, but still bad. And yet it seems to vary somewhat. I need to do a better job of checking and quantifying the leak so we can start a thread on Moss seals. Either way your seal kit will definitely be going in this winter.

Michael
 
Back
Top