Bad Positive Crankcase Vent Valve?

[TomG]

So Tom, my questions are:

• Is your blowby serious enough that the standard arrangement is no longer sufficient (and what does that tell you)?
• Or are you using the PCV system because it has been recommended and seems to be a better way to go even with resultant carburetor adjustment issues?

Neil,

I'm honestly starting to wonder why I've installed the PCV valve myself.

My engine is a rebuilt (2008) MMI version. I haven't run it long without the PCV valve, so I can't really say how much blow-by I have to start with. I installed it during the last winter refit/rehab period. The Admiral has a very sensitive nose, so I was attempting a preemptive strike at a potential complaint of "I smell something funny...". Although I've read many positive endorsements of the PCV valve upgrade, I don't recall reading any real negative reports. My curiosity centers on what I believe to be an unusual side effect of this change to my engine. If everyone else has the same problems with installing a PCV valve that I'm having, I would think I would find more problems reported.

I'm fine with a little richer idle mixture to compensate for the PCV valve, but my symptoms are asymptomatic. I'm going to try a new PCV valve tomorrow when I get home and see if that changes things. If it doesn't, I'll go back to the traditional tube.

I still have a nagging question: What are the symptoms of a bad PCV valve?

[Marian Claire]

I have often voiced my thoughts that the PVC system treats a symptom not the cause of blow-by. I acknowledge the PVC's help in maintaining a clean engine. I have to think of what would have happened if I had had a PVC when the rings in my #4 cylinder snapped. Without the PVC the blow-by was immediate and a obvious signal that I had a problem. Dan S/V Marian Claire

[ndutton]

Solutions

PCV valve stuck open = vacuum leak and poor running especially at idle (highest vacuum)
PCV valve stuck closed = cabin smells
PCV valve an improper match for our displacement engine = a combination of both.

Wifee's nose on alert = "Honey, would you take the helm? You're so much better at it. Can I fix you lunch? Would you prefer red or white wine?"

Seriously, I'd try it without the contraption and see how it goes. If you haven't in the past, consider running the blower during engine operation. Why continue to fight or compensate for an intentional manifold leak? You already know and I admit that's not the popular opinion but you're becoming the poster child for contraindication.

[TomG]

You already know and I admit that's not the popular opinion but you're becoming the poster child for contraindication.

Maybe I'm hanging with a bad crowd?

I'm not ready to throw the baby out with the bathwater just yet... I think there are advantages to the PCV system, I just wonder if my problems are caused by a defect in a single part Rather than a failure of a whole system. But I am keeping an open mind.

[Carl-T705]

Is it possible you have the PCV valve installed backwards? I not familiar with the system.

[Dave Neptune]

PCV should be a must if available

Guys, I may start a bit of contrversy here but here goes.
The PCV valve has been around a long time and for good reason. It was one of the first smog devises developed for the 4 stroke gasoline engine and it did not alter performance. When I tore down an engine before the advent of the PCV the engines wre coated with a thick layer of crud and sometimes under the valve covers there was just enough room for the rocker arms to move due to the build up. Now I will agree that the newer detergent oils have also helped but venting the unburned gasses (from combustion) is just part of the fumes developed inside the engine. The heat and friction also evaoprates the oils and gas fumes mix with them, get stick~goohey and just settle in the crankcase with whatever sticks to them to contaminate the oil. The oil picks up these contaminates which stick to everything and uses them to run through the oil galleys to slowly deposit throughout the engine. Even in a fresh new hand built engine there is a bit of blowby that accumilates and there is always fumes eminating from the oil to contaminate the air inside the engine and the oil.
With a POSITIVE CRANKCASE VENTILATION VALVE installed those gasses are sucked out of the engine and the nasty fumes are being replaced by clean fresh air.
I've been rebuilding engines sine the middle 50's and could tell just by looking inside that they did not have one because of all the KRAP inside. I just pulled down my Vett engine with 276,000 miles on it and guess what it was still clean inside. That engine had the cam go flat and destroyed the rings and bores on #'s 2&4. I actually ran spacers on the plugs to keep them from fouling for the last 75,000 miles until I was set to rebuild the 383 for another run. I would not run an engine without one unless it was just for racing as a racing engine gets torn down regularly and makes very little vac until it get to spinnign a bit.
Think of the PCV as an engine cleaner just as much so as an oil filter .

Dave Neptune

[smosher]

Dave, so I don't have a blowby issue, would it still make sense for me to install one to keep the insides clean ?

Steve

[ndutton]

Dave, so I don't have a blowby issue, would it still make sense for me to install one to keep the insides clean ?

And depending on how you answer that consider a follow-up question: does that mean the factory slash tube design is not effective?

[Ball Racing]

The slash was all they had in the 40's when they designed the A-4.
It wasn't until around 1967-68 that auto's used a PCV set-up.

The slash tube can do all it can, until the wear of the motor makes it so,
that newer technologies help.

It's one of those things, do I rebuild a the first smell of hot oil, or do you run a PCV valve, and rebuild when a compression test or oil pressure says I should...

[Dave Neptune]

Hmm!

Steve, why wait until it gets dirty to start keeping the insides clean.

Neil, yes the slash tube does have a bit of an effect but all it does is try to capture the fumes developed and direct them to the intake. It was trying to do what the PCV does much better. But all it does is catch what is forced out by the blowby itself. Whereas the PCV valve evacuates the gasses and as it is drawing it out the gasses are replaced by fresh air not just allowing the fumes inside to accumilate. There just is not enough suction on the spark arrestor to properly ventilate the engine and now we have the kits available .

There are a few issues with the PCV and some carb applications however not so with the A-4. In the early days of the PCV systems being installed as an aftermarket devise some performance engines required a bit of tinkering on the carb to compensate for the additional un-metered air in the idle circuit. However that was about all the issues I can remember and those were an easy fix.

The PCV does what it implies that is to positively evacuate the gasses while allowing fresh air in so all the gasses are evacuated~~a good thing for a new or old engine.

One of the troubles with our application in small boats is that the engine is in the living spaces and just because you smell a bit of hot oil smoke is no reason to necessitate a full rebuild.

Dave Neptune

[ndutton]

Remember, I said I was in the minority

It's one of those things, do I rebuild a the first smell of hot oil, or do you run a PCV valve, and rebuild when a compression test or oil pressure says I should...

Pretty much what I was saying. My position is if the blowby overwhelms the original set-up it's an indication of internal wear. From then on it's the owner's choice whether to treat a PCV system as a permanent or temporary fix.

And I'm hanging on Dave's every word, he da man with this stuff. I'm not in his camp on this, particularly the introduction of crankcase air into the manifold after the carb and that the carb has to be set differently with a PCV system. Tells me the PCV does have an effect.

I view this like an oil leak. Do you put a pan under the leak to catch the drippings or fix the leak?

And I want to point out (again) that this is what makes this forum the greatest, differing opinions with open, constructive discussion. By now every other forum I frequent would have degenerated into questioning one's ancestry.

edit:
Dave, you and I were typing at the same time.

In the early days of the PCV systems being installed as an aftermarket devise some performance engines required a bit of tinkering on the carb to compensate for the additional un-metered air in the idle circuit

How is this not applicable to our engines? Isn't un-metered air exactly what's going on?

I admit the PCV system sucks harder than the slash tube but the slash tube still is a negative pressure system, no?

[thatch]

"To PCV or not To PCV, that is the...."

If there is one topic that will draw a warmed up "discussion" it would have to be to add or not to add the PCV accessory. On virtually all of the "recreational" automotive engines that I have built or worked on over the years, PCV valves were never considered as being a necessary addition. When I acquired my first A4 a few years ago the timing was set at factory specs and the vent tube was installed correctly and there was virtually no blowby at Idle or after running hard for several hours. I mention ignition timing in this discussion because it can have a significant bearing on the amount of blowby that an engine produces. Currently there seems to be a mentality in the A4 community that "power tuning" is the way to set an engines timing. I admit that advancing the timing to the point of "near detonation" will increase the engines output but it will also increase the blowby in the process. Then comes along the PCV valve concept. At first it seems like a good idea until you realize that, at only 65 cu. in. there is not much of a vaccum signal to deal with, particularly at idle. I realize that these PCV valves are designed for small engines but, if you throw in even a small additional vaccum leak or if your intake and exhaust valves begin to show signs of leaking, this can completely foul up the delicate air/fuel ratio, which will normally show up at idle first. If I had to make a "blanket" reccomendation, it would be to, first fix the vent hose to it's correct position and secondly to set the ignition timing to a couple of degrees BTDC before considering the addition of a PCV valve.
Tom

[Dave Neptune]

Checked

Tom, I did some checking around with some rather good mechanics and we think you have a bad PCV valve or possibly the wrong one. The only other possibility is a big vac. leak and it would be large enough to hear over the din of the engine if you had the box open.
Since blocking your valve eliminated the problem the problem must now be with the valve.

Dave Neptune

[Ball Racing]

Then comes along the PCV valve concept. At first it seems like a good idea until you realize that, at only 65 cu. in. there is not much of a vaccum signal to deal with, particularly at idle.

Idle is when you Do have good vacuum in the manifold.
But not much air pulling through the flame arrestor.(from a closed throttle plate)

[TomG]

I just got an email from Tom at Indigo. He stated that it sounds like I have a defective PCV valve. Apparently, NAPA had a bad batch around the time I ordered mine. I'm off to NAPA to get a new one. I'll report back with my findings tonight.

Thanks one and all for your help and the invigorating discussion!