General PCV Question

My PCV on my freshly rebuilt B23ft is set up as follows: Stock breather box, with a 5/8" hose going to the pre-turbo pipe.

I'm getting some oil seal leakage, and today I noticed that I have a decent amount of positive pressure in the crank case at idle. (unplugged the 5/8" hose and felt the pressure from the crank case.)

I also noticed that at idle, the pre-turbo pipe doesn't pull much or any vacuum (not surprising, I guess, since there's not much restriction at the filter).

I already have a vented valve cover cap from which I'll be running a second 5/8" hose to the same pre-turbo pipe, but I'm wondering if I should be incorporating a smaller vacuum line from the crank case to the manifold, for vacuum at idle. With a one-way valve, of course.

It seems that a lot of stock systems have a small vacuum line form the manifold drawing vac on the crank case, but most people who run catch cans just run them back to the pre-turbo pipe.

Thoughts?

I was going over this with my boss (former engineer for Cosworth) a while back after I noticed my front main area collecting dirty oily ness. His thoughts are ideally both, crank vapor line (5/8" or so) to a catch can or recirculating vessel, line to manifold with a check valve that only opens under vacuum, second line to the preturbo that only opens when crank case pressure is above the level of the preturbo intake pipe. He said that the hardest part is finding reliable valves that open/handle the pressure you're running. So say your intake manifold sees 50kpa at idle, you want the valve there to be open until the manifold sees boost at 100kpa, then the preturbo line needs a valve that closes at anything less than 100kpa, anything higher and you'd see a vacuum leak causing idle issues. This puts your catch can under a continuous vacuum unless the cc pressure is positive, opening the catch can to the pre turbo pipe, which by that time should be delivering a slight amount of vacuum.

You could just run the catch can vented, with a check valve between the can and vent.

You may simply have too much blow by: rings not yet seated and need more time or the engine is not put together correctly (you can perform leak down and dry/wet compression tests to get better idea). Is the stock breather new or has it been cleaned?

A band aid for now may be just adding more vents. Small vacuum line going to the manifold is an emission part with little real function- it's not going to relieve crankcase pressure or cause problems even if it's completely clogged. So don't worry about that- concentrate on flow through the 5/8 hoses. The pre-turbo fitting with electrical heater built in it should be free of any sludge build up.

Unless the air filter is restricted you will not see vacuum pre-turbo. A little pressure drop at high RPM - may be, but the main reason the crankcase is vented to that location is emission regulations (air filter is a barrier to escaping crankcase fumes with engine off).

I would temporarily vent the crankcase to outside air and give it a thousand miles or so to see if there is any improvement with oil leaks and pressure.

You can put a cheap breather on the end of the hose to cut down on oil spitting out while you are running like that. Just feed a paperclip through the sponge or it will fall out. About $4 at Autozone:

It's the first engine I've ever built, so incorrect ring assembly isn't out of the question. I lined up all the gaps as they should be, and the gaps where all within spec. I'll give it more break in time and then do a leak down test. I'm not going to pull the motor back out any time soon, so if there's too much blow-by, I'll have to live with it.

The breather box on the block is clean and clear, and the hoses are new. I don't know about the pre-turbo fitting with the electrical heater you're talking about. I just have that 5/8" hose going into a rubber grommet in the pre-turbo pipe. I plan on running the 5/8" hose from the valve cover to another simple grommet on the pre-turbo pipe. Even though that location won't draw a vacuum, it should never see positive pressure, right? Seems like as long as it has less pressure than the hoses from the crankcase, the CC pressure will be able to escape into the intake tract.

cwdodson88 said:

I was going over this with my boss (former engineer for Cosworth) a while back after I noticed my front main area collecting dirty oily ness. His thoughts are ideally both, crank vapor line (5/8" or so) to a catch can or recirculating vessel, line to manifold with a check valve that only opens under vacuum, second line to the preturbo that only opens when crank case pressure is above the level of the preturbo intake pipe. He said that the hardest part is finding reliable valves that open/handle the pressure you're running. So say your intake manifold sees 50kpa at idle, you want the valve there to be open until the manifold sees boost at 100kpa, then the preturbo line needs a valve that closes at anything less than 100kpa, anything higher and you'd see a vacuum leak causing idle issues. This puts your catch can under a continuous vacuum unless the cc pressure is positive, opening the catch can to the pre turbo pipe, which by that time should be delivering a slight amount of vacuum.

You could just run the catch can vented, with a check valve between the can and vent.

Click to expand...

PCH said:

You may simply have too much blow by: rings not yet seated and need more time or the engine is not put together correctly (you can perform leak down and dry/wet compression tests to get better idea). Is the stock breather new or has it been cleaned?

A band aid for now may be just adding more vents. Small vacuum line going to the manifold is an emission part with little real function- it's not going to relieve crankcase pressure or cause problems even if it's completely clogged. So don't worry about that- concentrate on flow through the 5/8 hoses. The pre-turbo fitting with electrical heater built in it should be free of any sludge build up.

Unless the air filter is restricted you will not see vacuum pre-turbo. A little pressure drop at high RPM - may be, but the main reason the crankcase is vented to that location is emission regulations (air filter is a barrier to escaping crankcase fumes with engine off).

I would temporarily vent the crankcase to outside air and give it a thousand miles or so to see if there is any improvement with oil leaks and pressure.

You can put a cheap breather on the end of the hose to cut down on oil spitting out while you are running like that. Just feed a paperclip through the sponge or it will fall out. About $4 at Autozone:

Click to expand...

What was the ring end gap?

cosbySweater said:

What was the ring end gap?

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Can't remember off hand, but I think it was in .025 range. I remember checking them and being happy with them when I had the specs in front of me.

PCH said:

You can put a cheap breather on the end of the hose to cut down on oil spitting out while you are running like that. Just feed a paperclip through the sponge or it will fall out. About $4 at Autozone:

Click to expand...

This is a good idea, what exactly is that breather?

Tfrasca said:

I don't know about the pre-turbo fitting with the electrical heater you're talking about.

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Stock setup has a heated fitting. You will actually get better PCV flow without it because it restricts down to like 1/2" diameter from 5/8".

Uncleknucklez said:

This is a good idea, what exactly is that breather?

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Universal part for old style carb large round air filter housings.

PCH said:

Universal part for old style carb large round air filter housings.

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I would rather vent both 5/8" hoses to the pre-turbo pipe, just for the smell and feeling slightly better about my environmental impact. What would be the reason to vent to atmosphere rather than to the intake?

Simplicity. As a temporary setup only. You don't want to coat the insides of the turbo, IC, piping and manifold with oil given what appears to be higher than normal blow by. Yes it will smell but I think the priority for now is stopping the oil leaks and waiting for blow by to magically disappear (and I hope it will). You are not using Synthetic oil yet, right?

I admire your build BTW

PCH said:

Simplicity. As a temporary setup only. You don't want to coat the insides of the turbo, IC, piping and manifold with oil given what appears to be higher than normal blow by. Yes it will smell but I think the priority for now is stopping the oil leaks and waiting for blow by to magically disappear (and I hope it will). You are not using Synthetic oil yet, right?

I admire your build BTW

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Thank you. Hopefully my build makes it past the break-in time!

That makes sense about not dumping oil vapors into my intake if it might clear up in another 1000 miles or so. And no synthetic yet. I've done about 400 miles with break-in oil in it so far. Planning on changing that for Mobile 1 synthetic 10w30 in another couple hundred miles.

Does that sound reasonable?

Reasonable as long as there are changes for the better. Many different opinions on switching to synthetic after rebuild. I personally would do 3K miles on mineral first. Some industrial/tractor engine manuals recommend to keep original oil for 100 hours. (Hypothetically that's 100x30MPH average=3000 Miles). I remember buying a set of Mahle pistons with rings and the info sheet mentioned not using synthetic for like 5K miles after the install. In any case you don't want to do that with leaking seals.

You can fab a super big temporary catch can out of gallon bottle or a window washer reservoir or get a nice one from e-bay if you are really against venting to outside air. The key is to have a large volume to slow down the stream of vapors so they stick to something before settling in your intercooler. Then you will end up using gallons of gasoline to clean that oil from the IC and no really environmentally safe way to dump it anywhere- no recycler wants to take that stuff.

Yeah, it seems like adding the second 5/8" hose off the valve cover will be enough to prevent the seals from leaking any more, even if the blow by only gets marginally better. I don't see how I could still have positive pressure with two decent-sized breathers like that.

What's the reason for not using synthetic for so long?

PCH said:

Reasonable as long as there are changes for the better. Many different opinions on switching to synthetic after rebuild. I personally would do 3K miles on mineral first. Some industrial/tractor engine manuals recommend to keep original oil for 100 hours. (Hypothetically that's 100x30MPH average=3000 Miles). I remember buying a set of Mahle pistons with rings and the info sheet mentioned not using synthetic for like 5K miles after the install. In any case you don't want to do that with leaking seals.

You can fab a super big temporary catch can out of gallon bottle or a window washer reservoir or get a nice one from e-bay if you are really against venting to outside air. The key is to have a large volume to slow down the stream of vapors so they stick to something before settling in your intercooler. Then you will end up using gallons of gasoline to clean that oil from the IC and no really environmentally safe way to dump it anywhere- no recycler wants to take that stuff.

Click to expand...

"Seating" means wear, so you don't want the lubricant between two parts to be too good preventing parts forming better fit. May be an urban legend that started with the claim that synthetic is so much better, who knows. But synthetic is in fact a much better lubricant. It is also much more chemically stable and doesn't burn off as easy as mineral so if you start getting it into combustion chamber because the new rings didn't scrape it off the walls, it can foul up the plugs faster than mineral oil that would have better chances to burn off during combustion.

Older mechanics I've been around said that and did it this way so I believe that to be the way to do things. Adds to fun of playing with cars

That's sound enough reasoning for me. I'll plan on doing at least one more oil change with conventional oil before switching to the Mobile 1. Thanks again for all the help.

PCH said:

"Seating" means wear, so you don't want the lubricant between two parts to be too good preventing parts forming better fit. May be an urban legend that started with the claim that synthetic is so much better, who knows. But synthetic is in fact a much better lubricant. It is also much more chemically stable and doesn't burn off as easy as mineral so if you start getting it into combustion chamber because the new rings didn't scrape it off the walls, it can foul up the plugs faster than mineral oil that would have better chances to burn off during combustion.

Older mechanics I've been around said that and did it this way so I believe that to be the way to do things. Adds to fun of playing with cars

Click to expand...

Synthetic is chemically the same stuff as dinosaur oil - hydrocarbon soup plus a big pile of additives to clean the engine, prevent wear, help it stick to surfaces, improve heat resistance, etc etc etc.

The big difference is that when it's synthesized instead of distilled, the manufacturer has more control over exactly what is in that hydrocarbon soup which makes the base of the oil. Most importantly there's fewer impurities (undesirably long, short or weird hydrocarbons) in there, which are the ones that cook together and form sludge when the oil gets hot.

In terms of overall mechanical properties, synthetic should have about the same as conventional oil with a matching rating. Should burn just as well once it ends up in the cylinder, too. Might be a slightly better lubricant, therefore prolonging break-in, but I'd doubt it makes a significant difference compared to factors like RPM and operating temps.

All that said... I'd use conventional oil for break-in because it's cheaper. Synthetic is nice for the longer intervals once you have all the crap worn out. There's also more "specialty versions" with extra additives available in synthetic oil.

Thanks for this. While we're on the subject of break ins, RPM, and heat cycles...

What's your ideal break in procedure? I did a couple hundred miles with no boost, but a fair amount of full throttle accelerations, followed by decels. Now the boost is at 8 psi and I've been keeping it below 4k rpm (minus a couple times before I realized my tach is stopping at 4 for some reason). I'm at about 400 miles now.

I kind of thought that the cast rings would seat in the first couple hundred miles, and that by now the cylinder walls aren't rough enough to continue wearing them in. Maybe I should drop the boost back down and keep trying to break them in?

Khrrck said:

Synthetic is chemically the same stuff as dinosaur oil - hydrocarbon soup plus a big pile of additives to clean the engine, prevent wear, help it stick to surfaces, improve heat resistance, etc etc etc.

The big difference is that when it's synthesized instead of distilled, the manufacturer has more control over exactly what is in that hydrocarbon soup which makes the base of the oil. Most importantly there's fewer impurities (undesirably long, short or weird hydrocarbons) in there, which are the ones that cook together and form sludge when the oil gets hot.

In terms of overall mechanical properties, synthetic should have about the same as conventional oil with a matching rating. Should burn just as well once it ends up in the cylinder, too. Might be a slightly better lubricant, therefore prolonging break-in, but I'd doubt it makes a significant difference compared to factors like RPM and operating temps.

All that said... I'd use conventional oil for break-in because it's cheaper. Synthetic is nice for the longer intervals once you have all the crap worn out. There's also more "specialty versions" with extra additives available in synthetic oil.

Click to expand...

Tfrasca said:

It's the first engine I've ever built, so incorrect ring assembly isn't out of the question. I lined up all the gaps as they should be, and the gaps where all within spec.

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Just to be clear, did you put the gaps on top of each other in a single line when installing the pistons, or at 120 degrees (4, 8 and 12 o'clock)?

after I put my engine together I ran the cam in for 20 minutes with Joe Gibbs BR30 then dumped the oil and changed the filter. I refilled with more BR30 and drove it 'kindly' on back roads for a few hundred miles and changed it again. Then I put in regular synthetic and just drove it.