PCV installation results

[Rut]

I just had to do it! I installed a 1/8 nipple in the intake manifold and piped in a PCV from the oil separator. I have a Weber carb on a Pierce manifold and there is a boss just below the carb for tapping. I fired up the engine and it didn't want to idle (no surprise) and with the help of a little choke ran at about 2000 rpm. The rear end leak stopped completely! About a minute or two later I was killing every mosquito in the neighborhood! I had more smoke coming out of the exhaust than a barn fire. I disconnected the hose barb to the manifold and held my thumb over it and she settled in to a good 900 rpm idle and the oil flow returned. I also had oil bubbling out of the separator up thru the pcv. I must have applied a little too much vacuum, but it did solve my oil leak problem. Now I need to figure out how to regulate the vacuum so the engine will idle, won't suck up oil, and the rear leak will stop or slow to normal 1275 standards. Any suggestions out there?
Thanks, 'Ole Smokey'

 

[sqbsprite]

Is your valve cover vented? I have mine piped exactly the same way with no smoke at all. Yours is pulling so much vacuum on the oil separator that it is drawing out oil. If the valve cover is vented, it can pull enough fresh are through to equal out the vacuum. Possibly. I don't know. My line is much bigger than 1/8". I've been running this way for about 3 years now.

PCV is mounted right at oil separator

Valve cover vent

 

[JPSmit]

so theoretically you could test this by running it with the oil cap off? or is that too much air?

 

[Rut]

Let me clarify a bit. I have a nonvented aftermarket valve cover with an oil filler cap with a small (1/16") hole. The original design of the Weber carb/Pierce manifold had the 1/2" line coming off of the oil separator and into the underside of the air filter housing. The air filter is a foam rubber type which I'm not used to and it is dry. This set-up provided no vacuum to the oil separator/crankcase and the engine leaked like a seive. I tried to rectify this by installing a 1/8" hose barb into the intake manifold where I drilled and tapped a hole. I connected the hose from the oil separator to the 1/8" hose with a pcv inline. When I fired her up she did not want to idle and I used the choke to get about 2000 rpm. The oil leak stopped completely, but as you noted I started pulling oil from the separator. I then used a little redneck ingenuity and stuffed a ribbed wooden dowel in the plastic 3/8" reducer and slowed the flow to a trickle (tech term), hooked it back up and she idles at about 1000 rpm, no smoke, no leak. It doesn't take much vacuum to fix the leak and now that I know how much (WAG), I can start with a permanent solution. This car does not have a muffler on it, just a straight pipe with a split resonator and it's loud, but now that I have her idling with no oil leak I can play around a bit.

 

[Rut]

Continued...the engine sounds VERY mechanical with lots of clicks, clanks, and other noises that a modern engine does not make. It's been a long time since I've owned a British car (1972) and I didn't remember them making that much engine noise. Any ideas of what I need to listen out for? Oil pressure is 60-65 on cold start and drops to about 40 at warm idle. The po spun a main bearing on his 948 (original engine) and I want to make sure I don't miss something.
Thanks again, Rut

 

[sqbsprite]

I think you are now on the right track with the oil leak as I predicted in your post from a couple weeks back. It beats pulling the engine unless you have too for other reasons. As for the noise, it could be as simple as setting your valve clearances which is something you should do very soon. You have plenty of oil pressure. Have you had the valve cover off? You will need to check the rocker assembly for play also. Often, people neglect to replace the shaft and re-bush the rocker arms. These engines are not very noisy, but they definitely have a more mechanical sound since they have solid lifters.

 

[Billm]

It sounds from your writeup that you hooked up the vacuum pipe but didn't put in an actual PCV valve. If this is the case then your engine is operating exactly correctly. If you did put in a PCV valve and it is still smoking then you put in a defective valve and need to replace it with a good one.
BillM

 

[Rut]

Billm, I installed a pcv and after I reduced the vacuum/flow I have no smoke and I have no leak. I don't know if the pcv does anything more than reduce the diameter of the 2 hoses (from 1/2 to 3/8). I hope this clarifies my 'experiment'!
Thanks, Rut

 

[Billm]

It just reduces the size but more importantly is that it has two settings so that it can draw a correct volume at both high vacuum settings (idle) and low settings (higher throttle) so that it stops oil leaks all of the time but doesn't create a "smoke screen".
BillM

 

[nomad]

Sounds as if different PCV's might have different size orifice's. Is that correct? The only ones I've looked at other than the stock diaphram looked like nothing more than a check valve.

Kurt.

 

[Rut]

The main differences I've seen besides fit, most are 1/2" x 3/8", gravity or spring, straight or 90 degree. I checked several different sizes based on engine size and the flow thru each was pretty healthy. I would say check valve describes it pretty well. One knowledgeable parts guy suggested a metal gas filter with 1/4" barbs on each end. I think restricting the orfice on the intake side is key to proper function.
Rut

 

[aeronca65t]

.....I think restricting the orfice on the intake side is key to proper function.
Rut

Yes, I think that's right. On my race car, I couldn't stop the rear seal from leaking until I "tuned" the car to have the correct negative pressure in the crankcase. To start out with, I used an adjustable valve ~(similar to this)~ . I put the valve in the hose between the valve cover and intake.

Once I had things adjusted about right, I replaced the valve with a drilled orfice (this was quite a while ago......I think about 3/16" or so). This was in a 1500 cc car, so not the same as your's but similar concept.
Eventually, I changed this and ported into a spacer between the carb and manifold.
In my case, it only had to work well at +5000 rpm, so the broader speeds of a street engine might be more fussy.
I bet there's a regular PCV valve out there that would work, but with lots of trial-and-error.

G'luck and I'd be interested to hear how it finally works......I'm building a racing 1275 right now and expect to run into the same questions soon.

 

[Billm]

The valve is "almost" just a check valve- when there is low vacuum then it doesn't "reverse" to close off the flow but with high vacuum it almost shuts off but not all of the way (slow leak). Try it and you will see that it never truly shuts off in reverse flow (if it is still good). When it shuts off completely in reverse flow then it is time to get a new one since it isn't stopping oil leaks anymore.
BillM

 

[Rut]

Billm, thanks for the explanation! That is the first time I've seen it explained and it makes perfect sense. Now all I need to do is find a suitable pcv that has flow limits in the range necessary to make it function properly. I tried the Datsun 1200, but it's threaded on the 1/2" side. Steve, do you know the make and model number of your pcv? Any suggestions out there?
Thanks, Rut

 

[Billm]

Go to Pep boys or O'Reillys and get any one that has 1/2" barb fittings at each end. I have never heard of anyone having any problem doing it that way. I get mine off of the "generic" rack at O'Reillys (if/when I buy new ones)
BillM

 

[sqbsprite]

I think mine is by Purolator. The only number I see on it is 2273. It's 3/8" on both ends. My connection on the manifold is a 1/4" barb. I made it to replace the stock one.

 

[hooey]

one other point is you must install it the wright way
it is a one way valve ! I have seen lots if times that someone has put it in backwards
some thing also you might try is building a tank and mount the tank up high some where and running two hose out the bottom and one out the top run the two hose to the motor one in to the valve cover and the other one to the timming cover and running the top one to your pvc valve and then to the intake

 

[jlaird]

Have we been beating ourselves up over rear engine leaks when they can be solved with a hose from the intake to the valve cover with a 1/2 " barb fitting on each end?

Tell me I don't understand how this can be.

 

[Rut]

Billm, that's what I did and the one I have is for a Ford v8 truck. I didn't know that they restricted flow at different vacuum settings in the intake manifold. I tried to find one for a smaller engine with the right dimensions, but no luck so far.
Thanks, Rut

 

[nomad]

Interesting info!! It does make the original BMC complicated diaphram valve look more logical now though.
Keep us up to date.

Kurt.