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Hey y'all,
Since I built my 350 tpi I have had some little clues of a good amount of crank case pressure. Namely, the oil dipstick used to leak a bit now and again, pcv valve hose with a lot of oil outside of it, and just recently I noticed the oil fill cap was leaking down the valve cover. I replaced the fill cap and the pcv valve and today, during the final ride of the year, I smelled oil after giving it gas. The pcv valve had been ejected from the valve cover. Are these all normal things or are these clues of too much internal pressure? If so, what can I do to help it aside from a breather?
Does the PCV valve fit tight in the grommet? If you have enough blow-by to pop the PCV valve out, then your rings are shot.
What do your spark plugs look like? When you "get on it", do you see a cloud of oil smoke behind you?
How is your engine venting set up? Pictures help a lot.
Breathers are for letting filtered air INTO the crankcase, not blow-by out.
The correct setup is to have a PCV valve in one valve cover which works at idle and part throttle (high vacuum) AND
a hose/tube connected to the "air filter" that routes to the other valve cover, that sucks the blow-by vapors into the engine during low vacuum conditions (WOT).
There is nearly NO vacuum at the PCV valve at WOT.
Sorry guys for not enough info. Engine is a GM crate with roughly 300 hrs on it (someone had it in a nova project, then pulled it to do an s10 project - but sold the truck and already got a motor for the nova) when I got the motor I checked the heads and it totally even to substantiate the story. Never checked the compression but whole long block looked good. Only suspect item was the oil pump looked new, and it had an obviously new oil pan gasket.
Once securing the engine, I put on summit racing aluminum Heads, crane 2032 cam, Accel base manifold, SLP runners, 24lb Bosch injectors, afpr, and egr/emissions delete. I have put maybe about 4,000 miles on this motor since I put it in 5 years ago.
The pcv valve is new, and it doesn't fit quite as snugly as the old one. The old one took a little effort to get out, this one slides in and out somewhat easily but doesn't just drop in either. I don't remember ever having a tube from other valve cover to the intake. The valve covers on it now are TPI Vette covers and don't have another tube.
i don't have time today to pull the spark plugs but I will one of these days. The oil that was on the old tube looked sort of like condensation but smelled oily so I figured that it was such. But I haven't seen this "condensation" on it in a while. I put it in quotes cuz although it looked like condensation, it was still there when the motor was off. I haven't seen it since I degreased the engine bay before the last car show I was in.
I honestly don't think there's an issue with the rings, there was no sign of scoring or anything on the cylinder walls when we looked at it. Maybe I'm just over reacting and this is just a series of unrelated coincidences?
Well, pull the fill cap with it idling, see if you can feel air puffing out.
The new oil pump makes me wonder if the PO stuck a high pressure pump in there thinking...well, wouldn't know what he/she was thinking.
But, you probably should do a leak down test and see what shape the piston and rings are in, when you had the heads off I'm hoping you could still see a real crosshatch on the cyl walls, vs a bottle brush hone job? Nothing wrong with the bottle brush, but would just mean it had many more miles on it than you were led to believe.
Let us know if it was looking like machine honed cylinder walls or not.
The valve covers on it now are TPI Vette covers and don't have another tube.
Geez, just pulled the top-end off of my kids TPI, memory fading though, but I think the PCV plumbs to the plenum or TB. Search for some underhood shots, you'll spot it.
Geez, just pulled the top-end off of my kids TPI, memory fading though, but I think the PCV plumbs to the plenum or TB. Search for some underhood shots, you'll spot it.
Yes it plumbs to the plenum. Which is what this one does too. There's no separate hoses anywhere else though.
Well, pull the fill cap with it idling, see if you can feel air puffing out.
The new oil pump makes me wonder if the PO stuck a high pressure pump in there thinking...well, wouldn't know what he/she was thinking.
But, you probably should do a leak down test and see what shape the piston and rings are in, when you had the heads off I'm hoping you could still see a real crosshatch on the cyl walls, vs a bottle brush hone job? Nothing wrong with the bottle brush, but would just mean it had many more miles on it than you were led to believe.
Let us know if it was looking like machine honed cylinder walls or not.
I can't remember if there was cross hatching. But I do know that we had checked the cylinder walls and they were all in perfect shape absolutely zero ridge. I will have to check on if there is pressure out of the fill cap too.
What would it mean if there was a high pressure oil pump in it? Would that be no good? The original owner had obviously not tinkered with it since it still had the original cast iron heads and stuff (not removed - obvious from shape of heads and gaskets).
What you want to do is create air flow through the engine that sweeps the crankcase. Getting it wrong is unhealthy for the engine.
Air moves from high pressure ---> low pressure. The "high" pressure side is atmospheric. The "low" pressure side is inside the intake manifold where pressure is in vacuum (below atmospheric). I'm more familiar with LS engines, but if I remember right the intended pathway for SBC engine is air (at atmospheric pressure) enters the cylinder head valve cover, sweeps through the crankcase, and goes out the other cylinder head valve cover to the intake manifold (low pressure region). If you don't create that pathway, then it doesn't work. And you want to keep air momentum moving in that pathway by avoiding non-value added paths that churn the air in circles, or diverts air for no good reason, or slows momentum toward the intake manifold.
Now wide-open-throttle (WOT) condition is different. At WOT there really isn't hardly any appreciable pressure difference between atmosphere and intake manifold, so the momentum of air flow is interrupted. But pressure is building up in the crankcase faster than ever, especially at high engine speed. So what happens is every hole in the engine begins spewing crankcase vapors. If the natural venting of the engine isn't sufficient then you blow stuff out of holes and such.
Sounds to me like your engine venting is corked up too tight and you just need to open up more air flow to relive the internal pressure.
I can't remember if there was cross hatching. But I do know that we had checked the cylinder walls and they were all in perfect shape absolutely zero ridge. I will have to check on if there is pressure out of the fill cap too.
What would it mean if there was a high pressure oil pump in it? Would that be no good? The original owner had obviously not tinkered with it since it still had the original cast iron heads and stuff (not removed - obvious from shape of heads and gaskets).
I was thinking IF there was no cross hatching, or it was freshly done manually, someone may have re-ringed a worn motor and put a high pressure pump in it. And if it was re-ringed they may have thought high dollar rings would help vs cast, and honed it with the wrong grit stone, but since you're sure the heads were never off, we can put that to rest.
Now, there was mainly just carbon above the compression ring fit on my kids car, no discernable groove, but no cross hatch left after 150/160K miles.
There should be something plumbed into the pass side valve cover too, right? I just pulled things apart a few weeks ago and can't recall.
I can't remember if there was cross hatching. But I do know that we had checked the cylinder walls and they were all in perfect shape absolutely zero ridge. I will have to check on if there is pressure out of the fill cap too.
What would it mean if there was a high pressure oil pump in it? Would that be no good? The original owner had obviously not tinkered with it since it still had the original cast iron heads and stuff (not removed - obvious from shape of heads and gaskets).
I was really wondering about the crosshatching to try and draw a conclusion.
I was thinking IF there was no cross hatching, or it was freshly done manually, someone may have re-ringed a worn motor and put a high pressure pump in it. And if it was re-ringed they may have thought high dollar rings would help vs cast, and honed it with the wrong grit stone, but since you're sure the heads were never off, we can put that to rest.
Now, there was mainly just carbon above the compression ring fit on my kids car, no discernable groove, but no cross hatch left after 150/160K miles.
There should be something plumbed into the pass side valve cover too, right? I just pulled things apart a few weeks ago and can't recall.
My old 305 tpi had 180k miles and a noticeable ridge. The cylinders were oblonged over time, same was a 350 tpi I bought before this (long story short, the coolant passages cracked in the block). I have nothing plumbed into the passenger side, and I don't remember there ever being anything on pass side
To keep oil inside the engine and prevent crankcase pressure from building up at wide open throttle,
Use the post-air filter tube, with a high quality PAPER air filter if possible, to pull on the crankcase at Wide Open Throttle.
Like this
This is a factory setup. All cars come this way from the factory, even turbocharged vehicles use this method.
It is absolutely essential for a high performance engine to utilize some form of WOT pcv action,
typically in race cars this is done using an belt-driven vacuum pump. However for daily drivers, the added maintenance and cost of vacuum pump is not wanted. So we use the intake pressure drop instead, to protect the engine.
Of course you can run without this little detail, use a simple 'breather', but that will never keep the pressure below 101KPA at WOT, so it does NOT count as a PCV solution, and it WILL create oil leaks and contaminate the oil quickly, depending on how bad the blow-by (ring / wall conditional) is
Thank you everyone for the suggestions and ideas. It's pretty apparent I'm gonna have to do some more investigating and get back to everyone. Like I said, pcv valve isn't very tight, and the old oil fill cap was 30 years old. Again, not sure if this is all just a coincidence or all related. Going to fire it up again (was getting ready to put it away for the winter) and see if I'm getting puffs of pressure out the fill cap and take a look at the plugs. I'll keep everyone posted in the event I find anything.
Had a few minutes today to take a quick look at the car. I pulled a couple plugs (pictures attached) and ran it with the oil fill cap off. If I rev it to pretty much full throttle, I can feel a slight puff coming out, but nothing that felt to me that it would be enough crank case pressure to push out the pcv valve.
Also, I found out that I'm an idiot and there is another vent tube on the passenger side....and I've only had the car for 13 years and been working on it since then.
I took a couple pictures of the valve cover venting, but it's factory so there's not much to do there.
2. crankcase pressure test
using only 1 or 2psi (or less) manually pressurize the crankcase to find all leaks
Final all entry and exit points for crankcase, such as dip stick, breathers, etc...
Determine which of those points is necessary, remove any passive 'breather' type fixtures,
The only fresh air tube (breather supply tube) should come from just after the air filter, check #4 below
3. test and/or replace pcv valve
4. ensure the engine is using both manifold vacuum driven PCV (like seen in the picture, the pcv valve from valve cover feeds the intake manifold)
AND
ensure that you have some form of WOT pcv like I posted above, by connecting the fresh air breather (NON-pcv valve hose which supplies fresh air to crankcase) to the post-air filter tract
2. crankcase pressure test
using only 1 or 2psi (or less) manually pressurize the crankcase to find all leaks
Final all entry and exit points for crankcase, such as dip stick, breathers, etc...
Determine which of those points is necessary, remove any passive 'breather' type fixtures,
The only fresh air tube (breather supply tube) should come from just after the air filter, check #4 below
3. test and/or replace pcv valve
4. ensure the engine is using both manifold vacuum driven PCV (like seen in the picture, the pcv valve from valve cover feeds the intake manifold)
AND
ensure that you have some form of WOT pcv like I posted above, by connecting the fresh air breather (NON-pcv valve hose which supplies fresh air to crankcase) to the post-air filter tract
To keep oil inside the engine and prevent crankcase pressure from building up at wide open throttle,
Use the post-air filter tube, with a high quality PAPER air filter if possible, to pull on the crankcase at Wide Open Throttle.
Like this
This is a factory setup. All cars come this way from the factory, even turbocharged vehicles use this method.
It is absolutely essential for a high performance engine to utilize some form of WOT pcv action,
typically in race cars this is done using an belt-driven vacuum pump. However for daily drivers, the added maintenance and cost of vacuum pump is not wanted. So we use the intake pressure drop instead, to protect the engine.
Of course you can run without this little detail, use a simple 'breather', but that will never keep the pressure below 101KPA at WOT, so it does NOT count as a PCV solution, and it WILL create oil leaks and contaminate the oil quickly, depending on how bad the blow-by (ring / wall conditional) is
Sorry to be so ignorant on this, but could you find a picture of this application? I can't seem to figure it out in my head. Thought I knew a decent amount about cars and engines and I'm always humbled once I get on this site
Sorry to be so ignorant on this, but could you find a picture of this application? I can't seem to figure it out in my head. Thought I knew a decent amount about cars and engines and I'm always humbled once I get on this site
Hmm its a factory PCV route. Simply pull up the OEM pcv diagram for any vehicle made from 1998-2015 or so. I would imagine they are entirely similar.
I think I know what you mean though, you want a real life picture
Here is mine, a real life setup. I label it for you.
This the WOT pcv side.
valve cover feeds intake tube, post air filter, during WOT.
During idle/cruise, its reversed: post air filter tube feeds valve cover fresh air.
The key to note is airflow entering the crankcase during idle/cruise is filtered by the high quality paper air filter element.
The next key to note is during WOT, the pressure drop behind the paper element provides a PCV 'suction' to the crankcase.
there is no check valve / pcv valve in this line.
On the other side of the engine, is simple valve cover -> pcv valve -> intake manifold. Also, exactly like stock. Exactly like the picture you posted above of yours.
These two 'sides' work together to keep a low pressure in the crankcase at all times.
Can you see the pcv valve tied to the intake manifold near the back of the engine?
Notice they are on separate sides. This promotes a flow through the crankcase (as someone mentioned above) another critical aspect is that the flow should sweep through the entire crankcase during idle/cruise to prevent stagnant recess for forming.
I'm so sorry to be so dense with this....so on the passenger side of this engine is a tube from valve cover to throttle body. This isn't quite the same? Would the idea be to have a "T" in this line and install the paper filter? I know this is probably simple for everyone else but I don't know why I can't figure it out
I'm so sorry to be so dense with this....so on the passenger side of this engine is a tube from valve cover to throttle body. This isn't quite the same? Would the idea be to have a "T" in this line and install the paper filter? I know this is probably simple for everyone else but I don't know why I can't figure it out
depends where on the throttle body. That location is vague. Throttle body could mean:
1. ported vacuum slotted control line
2. full time engine manifold pressure
3. pre-blade pressure drop region
4. fully forward, near atmospheric region
What you want is the tube from valve cover, to feed from the engine's air filter. Get it away from the throttle body if you aren't sure whats happening inside the throttle body.
Move it towards the air filter.
Look at the picture I posted. See where the valve cover attaches to the intake air filter tube, just behind the air filter.
Anywhere between the air filter, and the throttle body is fine. But once you cross the threshold of the throttle body you need to know exactly where the air is coming from, as it could be any of those 4 regions. Throttle body is not a simple design, there are many difference ported/source vacuum tubes for various emission control devices. Perhaps somebody tied the wrong vacuum port to the wrong tube or something (happens all the time on 4-cylinder engines)
perhaps this picture is more clear? You can see where we take valve cover to post air filter tube
Note where the 'PCV at work' arrow enters the tube WELL before the throttle body. This is to eliminate any confusion about what the pressure source should be like. i.e. It needs to be a post-air filter pressure drop. You can measure this using a gauge that reads 0" to 40" of Water for example. Roughly
also the only paper air filter on the engine should be the one and only air filter for the engine. The big cone looking thing is just a random filter type; there are square ones, funny shapes, you can use any paper air filter you want as long as its the only air filter on the engine.
There it is (above) - as simple as it gets. Great picture and explanation.
Re-read post #3 while looking at that picture. Then you should understand the concept.
Last edited by NoEmissions84TA; 12-07-2019 at 09:36 PM.
Been doing some looking around on the net and been seeing some posts in Vette forums of not having enough pressure from that throttle body tube into the p/s valve cover for modified or cammed engines. It does appear tho that the air coming from the throttle body is before the blades. I've seen some posts where people have put a breather on to satisfy this, but I also understand the idea of coming off the intake tube (finally -- sorry I'm slow)
Been doing some looking around on the net and been seeing some posts in Vette forums of not having enough pressure from that throttle body tube into the p/s valve cover for modified or cammed engines. It does appear tho that the air coming from the throttle body is before the blades. I've seen some posts where people have put a breather on to satisfy this, but I also understand the idea of coming off the intake tube (finally -- sorry I'm slow)
Almost.
The pressure to draw on the crankcase at WOT has nothing to do with the cam/engine/modified.
Adding a breather 'breaks' the pcv system and renders it useless.
These things are done by people who don't understand how pcv works.
In reality. The pressure drop to drive the pcv at WOT comes from the air filter. Its why I keep saying to use a paper element, like factory uses.
It's no coincidence that paper filtration is superior and restrictive, and I will give you an example to help 'see' what happens
Here is the engine without any air filter at WOT
Notice that without the air filter, the pressure 'in front of' the throttle body is equal to atmospheric pressure (14.5psi) Making PCV unavailable at WOT, regardless of what is done to the engine. ---> In other words, PCV at WOT is a function of air filter pressure drop. <---
The air filter acts as a restriction. Think of what happens when you put your hand over the air intake tube, what happens to the pressure inside the tube?
Imagine that the engine is at WOT and you cover the intake tube completely with your hand. What will the pressure 'do' inside the tube?
answer: As you cover the tube with your hand (or a sock or something) the pressure will gradually drop there, it becomes a vacuum.
This is how you can satisfy the pcv system. By generating a vacuum in the tube by "closing the tube with your hand" (air filter's job) You can create any pressure drop you wish for inside the crankcase, since the tube is connected to the crankcase via factory hose "FRT"
You can modify the air filter quality (larger / smaller, paper element) to provide any amount of 'suction' at WOT that you deem is necessary to drive the pcv at WOT.
In most cases, it is enough to simply install a large paper air filter element, as paper has a tendency to provide high quality filtration and immediately pressure drop to 1 to 1.5" Hg is typical. This is why the factory uses them; they are superior filtration elements and provide the WOT pcv action to keep a healthy engine.
But sometimes the factory element isn't big enough (not your problem, just an example to help learn how this **** works):
for example, if you had an engine with opened ring gaps and running lots of boost pressure, you no longer have a factory PCV situation, and now have two new issues:
1. the engine flows more than it used to (we say the flow rate has doubled with engine power doubled)
2. the engine produces more blow-by than it used to (open ring gaps, plus boost)
The knee jerk reaction to people installing forced induction and doubling their power output is to remove the air filter or use a very free flowing air filter, without measuring the affect it has on PCV at WOT. This blind move cripples the pcv system and leads to an early engine demise for various reasons, it will leak, it will smoke, they won't know why. It will take time (years, many miles) so the effect is not immediately apparent (like smoking) but over time leads to many issues.
It might seem like we are using PCV to 'suck out the nasty vapors' and to some extent this is true; the thing about pcv that everyone seems to miss is that it also improves ring seal when done properly, so by using a proper 'size' air filter and pcv WOT configuration what you are really looking for is an improvement to the ring sealing and reduction in blow-by in the first place, a reduction in the production of nasty vapors to begin with. To put it simply, you can't reduce blow by without sucking up the blow before it happens, due to the effect blow-by pressure has on rings from below the piston inside the crankcase. In racing and money competitions this is generally done using a vacuum pump. But for street cars, we want minimal maintenance, so that is not feasible. Nevertheless, keep in the back of your mind that the intake pressure drop is not the only way to pull a active PCV at WOT, you could use many other devices to do that, such as venturii-exhaust driven system.
couple things to mention also
A. In your diagram, see where it says
"proper operation of pcv system depends on sealed engine"
this is why you need to perform the crankcase pressure test I outlined in a post above.
Without fully sealing the engine and finding every potential leak the pcv system will not function optimally or at all.
B. pcv maintenance
the pcv tubes get crusty, crud, sludge, so make sure they are all cleaned out and replaced as necessary. replace the pcv valve also IMO if its old.
also good job pulling up the diagram and following through. Ask any questions we are here to help!
Today I had a chance to get a vacuum gauge and threw it on the car. (First I should note, I removed the hose from the pcv out and took the vacuum reading off the hose going into the intake manifold. I mention this cuz I'm not sure if it's right but I couldn't find an easy spot anywhere else)
I got 15 HGin steady. It would go to 0 if I flipped the throttle real quick, but wouldn't stay at 0 if I flipped it and held at like 2000 rpm.
When I was checking hoses, I found that the hose from throttle body to the p/s valve cover seemed to have oil in it. Not much, but just a bit inside and around it, but enough to get on my hands and notice it in there. If the purpose of that line is to feed air from the throttle body into the valve cover, then I would think it's a bit concerning to see oil in this vicinity. Now that I'm remembering tho, while I was building this engine, I used a throttle body that was not off of my original tpi setup. I did this because I was polishing parts while I was waiting for install weather. Maybe there is something wrong with this throttle body?
Wanted to update everyone on this so far, even if you don't care lol.
That is how you pressure test the intake manifold. What you did with the gauge was test engine vacuum.
that is not a crankcase pressure test or intake manifold test.
Not sure you are aware what is going on yet.
Next,
To measure PCV system pressure, it requires a gauge with a resolution that reads in inches of WATER.
The gauge you are using is likely inches of MERCURY
1" Hg = 13.6" of water
You'd like to see approx 20" of water inside the crankcase at all times. Between 10 and 25" of water is typical.
So a gauge that reads from say +30" to -40" of water would be close to ideal.
--other units--
between +2" Hg and -4" Hg
or
+1psi to -2psi
----
Finally if your goal is to determine whether the throttle body is providing the correct vacuum or not,
the hose for FRT that goes to the throttle body should NEVER have vacuum signal present. Please re-read my notes about the throttle body behavior and different locations.
You want a location AWAY from the throttle body where pressure NEVER drops below say 25" of water.
That is how you pressure test the intake manifold. What you did with the gauge was test engine vacuum.
that is not a crankcase pressure test or intake manifold test.
Not sure you are aware what is going on yet.
Next,
To measure PCV system pressure, it requires a gauge with a resolution that reads in inches of WATER.
The gauge you are using is likely inches of MERCURY
1" Hg = 13.6" of water
You'd like to see approx 20" of water inside the crankcase at all times. Between 10 and 25" of water is typical.
So a gauge that reads from say +30" to -40" of water would be close to ideal.
--other units--
between +2" Hg and -4" Hg
or
+1psi to -2psi
----
Finally if your goal is to determine whether the throttle body is providing the correct vacuum or not,
the hose for FRT that goes to the throttle body should NEVER have vacuum signal present. Please re-read my notes about the throttle body behavior and different locations.
You want a location AWAY from the throttle body where pressure NEVER drops below say 25" of water.
I understand about the location away from the throttle body. At this point, I am testing this as a control. I want the same environment as when I first had the pcv valve eject from the cover. After that I feel I'll have a better idea of the health of the engine and be ready to make modifications to the system.
And yes, I couldn't quite figured out a way to read the crank case pressure, so I figured this test was a good one to do to make sure I had proper vacuum. From what I understand, improper vacuum can be indicative of valve issues, compression issues, or other problems. I figured this was a good start on my way of diagnosis. I think I have a better idea of how to get crank case pressure measured. I'll try to test that out next chance I get. Thank you again for all your help
Figured I'd update. Haven't had much time (or room in the garage) to get some testing done, but when I was trying to do some of the pressure tests attached, I noticed the oil dipstick feels somewhat loose. Specifically, it wobbles side to side pretty liberally. I believe if this isn't sealed properly, I would be venting pressure and vacuum there. I have no spots of oil, and under the car is bone dry, but maybe there is still an air leak too. I'll have to try and find more time after the holidays to get a better idea of what is going on though
Its typical for crankcase to develope multiple leaks over 20 years, this is why we do the pressure test. Dipstick is no exception and very commonly an issue.
The more boost you run the more important these pressure tests become. Being NA is like having a leniency. Nevertheless its still important.
Just remember all we are trying to do is restore the engine to its former, original, factory configuration/cleanliness, with any minor updates wherever possible. (i.e. higher quality parts such as pcv valve/hoses/fittings) Just like when you buy a 25 year old car and inspect/replace all the original rubbers in the suspension with new ones, sometimes better ones.
Its typical for crankcase to develope multiple leaks over 20 years, this is why we do the pressure test. Dipstick is no exception and very commonly an issue.
The more boost you run the more important these pressure tests become. Being NA is like having a leniency. Nevertheless its still important.
Just remember all we are trying to do is restore the engine to its former, original, factory configuration/cleanliness, with any minor updates wherever possible. (i.e. higher quality parts such as pcv valve/hoses/fittings) Just like when you buy a 25 year old car and inspect/replace all the original rubbers in the suspension with new ones, sometimes better ones.
I agree with the restoration. I'm going to rtv the dipstick sometime soon (off the road for the winter) and I'm probably going to get rid of the factory pcv breather tube on the passenger side. The rubber fittings are worn and cracked and a quick Google search shows only places selling are eBay for $94. I'll replace with a rubber hose and take it from my intake tube (right after my MAF (home made intake )). I don't really expect to have any other issues honestly. My dipstick tube has never lined up right with the header bolt to mount it with these heads since they're a bit taller. I'll secure it properly and if I have any other issues I'll report back. Thanks to everyone for the help, guidance and education.
12-06-2019, 04:07 PM
