I know a small-block Chevy is not the same thing as a 5.0 Ford engine, but I thought I should mention a problem that may be considered.
I had a problem with my '90 Lincoln TownCar fouling the #8 spark plug only when doing interstate cruising at 70 mph.

I would pull the plug and clean it, it would never foul around town, but it would oil foul in about 30 miles on the interstate.

There was no problem with the mechanicals in the engine at all -- in fact, the engine mechanicals were excellent.

The problem, and I proved this beyond any doubt, was the rubber seal in the back of the manifold that the PCV valve sits in had hardened with time resulting in a very small leak, and the PCV did not function properly.
Simply replacing this $2 part eliminated the problem completely.
If I put the old seal back, the problem came back.

Here is what was happening:
On a 5.0 Ford engine, the last valve in the right bank is an exhaust valve, the last valve (#8) on the left bank is an intake valve. The engine slopes downward toward the back.
At 70 mph, because the crankcase pressure in the lower part of the block would build up due to the hardened (and leaking) PCV valve rubber seal, would push upward at the oil returns keeping the oil from returning down to the bottom of the block. This caused the oil to pool around the last valve on each side. The last valve (#8) on the driver's side is an intake valve. Even though the valve seal, guide, and valve stem were in excellent shape, that valve would suck oil and foul in an just 30 miles after being cleaned.
I even pulled the valve cover and ran a rod down the oil return from the head to the bottom of the block to make sure it was not partially plugged.

I kept thinking that a simple "hardened" PCV valve seal could not be the cause of this, so I changed back and forth several times -- it fouled the plug with the old seal every time and NEVER fouled it with the new one once in 70K miles after that.

So, I do believe a very small (read this as minute) leak in the PCV system can have very unexpected results at high rpms. And, I do believe a small amount of excess crankcase pressure can keep the oil from returning from the heads.

I found out later that many 5.0 Ford engines have been replaced for the problem of #8 cylinder fouling plugs. I am betting many, if not most, could have been fixed with a simple PCV valve seal -- cost $2.
With the new PCV valve seal, this engine got over 3K miles to a quart of oil.
I change oil at 3K miles, so it could have been a lot more.

I know the small-block Chevy does not have an intake valve as the last valve in either bank, but I do believe that crankcase pressure can have something to do with this.

As an added note, I do have the old style AFR 190cc LT1 heads on my '92 Corvette with over 40K miles on them and I have never had a problem.

Tom Piper

 

Tom,

I had the same problem on my L-98 race motor with 195cc AFR heads. The oil return passages on the AFR head are much higher up on the head than the stock head. As a result a pool of oil builds in the valve cover, as much as a quart total in both covers. I had trouble with the oil being blown out of heavily baffled oil breathers. I finally wound up building an oil breather system that ran from four baffled breathers on the valve covers to an oil seperator can, the return line draining the valve cover oil back to the pan. I also added two drain lines per side draining oil from the valve cover directly back to the pan.
This is not a new new problem with AFR heads and is something they are quite aware of. I read a preview of their new LTX head design in a magazine and they they claimed to have solved this problem with the LT-1 /LT-4 design. I gues they haven't.

Larry

 

do you have any pics to post ?

 

From what I am reading on this post ALL "drain back" problems have in common is the high volume oil pump. Really on a street engine there no GOOD reason for having this on a street engine. Having said that all you need is a stock pump thats able to maintain 10 psi per 1000 rpm, in other words if an engine is able to spin up to 7000 rpm you need 70 psi to make the engine live. Now the hi volume pump will empty out a oil pan and send all that oil up the the heads and valley area., and still starve the bearings because the oil is gone elseware. When you think about this all the volume is needed is to "clean" the bearings and to have enough flow to cool the bearings, and a stock volume type pump fits the bill.
I also think and I maybe wrong, that people think volume is what keeps the bearings from contacting the journals... it's the oil film and pressure that does that not volume.

 

Yeah, it's out of control I think it was 1850. at the time for mine. The flow numbers advertised in the catalog (250ish @500)were actually smaller than sent (276@500), the cc. was as you stated. I am afraid to talk about mine, as I read everyone else's experiences, they might become mine.

 

[QUOTE=grapeknutz]From what I am reading on this post ALL "drain back" problems have in common is the high volume oil pump. QUOTE]

No, In my instance it was a standard volume pump.

In a SBC Chevy there's a pressure bypass in the oil pump itself that regulates the oil pressure. Unless you have problems in the motor itself with oil hemorages, all the high volume pump is going to do is bypass more oilback into the pan or pickup depending on the pump design.

 

Larry, the heads I have were purchased over a year ago. My second set is still in the box brand new. In Glens car with the engine just idling, the oil level in the heads is just above the bottom of the valve cover so that means that if you were to remove the valve cover you would have oil running out of the head! The drains are much higher than stock, the valve spring pockets are totally submersed in oil. The pump in the engine is a high pressure, and high volume pump. So in theory it isn't going to bypass as much oil as say a low pressure high volume pump. And at high RPM I am thinking that its going to flood the top end even more, so with the present drains the level will rise even more, perhaps over the top of the valve seals. The one time I removed the heads right after a 6500 RPM dyno pull, where the engine was ramped down by the dyno, and immediately shut down. There was enough oil in the piston dishes that you can poke your fingers into and it would be wet. I estimated at least 2 teaspoons of oil, enough so that the oil filled the bottom half of the dish in the each piston!

The problem I have is that this engine uses oil at a rate of 2 quarts per hundred miles if its driven HARD. If you drive it like grandma, then the oil usage is more reasonable for a race prepped engine. I know that there is NO WAY that this amount of oil can pass through the rings, if it did there would be other problems. Other than the intake gasket there is no other way the oil can get into the combustion area other than rings or valve seals. And I beleive I have a excellent gasket crush and I even applied a light coating of "the right stuff" on the intake gasket. Its been torqued and retorqued, so I don't think its the intake gasket so that leaves the heads.

 

Tom
It is the heads, thats why I sent them back to AFR. In Tony,s new thread he talks about it. I think AFR should make good on this problem. Thats just the price of doing business.
Regards

 

[QUOTE=SloRvette]Not nescessarily! the by pass in the pump does regulate pressure at a higher volume! Your are still going to have alot of oil volume still being runned thru the engine.
Now lets say if you had a standard pump and you are still "filling " the valve covers up with oil you may have to restrict that amount of oil. One old school way is to stick thru the valve push rods a pipe cleaner which will cut down the oil flowgoing to the head. This happens because the lifter is the regulator of oil going to the head, and if the lifter is after market, they may have the restiction hole too large and thus it will cause that trouble.

 

Tom,
If your seeing oil in the piston valve pockets your pulling oil in through the valve guides. There is no other way. If that much was blowing past the rings, you would see it on the plugs. If the top of the valve seal is in oil its going to suck oil in through the guide, vacumm and physics don't lie. If you find a different reason please let us know. Good luck.

Larry

 

Interesting. Since I last posted I've had a breather on my pass. side v.cover, and I'm mysteriously downa bit of oil. I think I'm going to put the tube back on to the TB. I also found out I have a High 'pressure' pump, which pumps the same volume but at a higher pressure. I'm thinking to have it removed for a standard pump.

Relating to the one post with the 5L ford engine, funny as it sounds my plugs are more fouled rearwards. Meaning my plugs at the front half are perfectly clean and get black towards the back. i'm thinking that After a WOT run the heads are full of oil and the vaccum is sucking the oil right through the guides. I'm using LT4 GM heads so I can't see this being a AFR problem alone, although if they do have higher drainbacks I can see why it's a problem.

Possible solutions ? Enlarge the drainbacks on my LT4 heads, and remove the high pressure pump for a stock volume ?

BTW whats a Canton 'balance' pump.. forget where I read it in this thread.

 

Wanna read more posts from guys experiencing the same oil drainback problem? Check out the ThirdGen.org site.

Same thing going on there.

Jake

 

AFR heads may have a higher drainback and help the problem along.
But, I believe the major problem is crankcase pressure -- eliminate that, and I think the problem will be gone.

With excess crankcase pressure, you have sucking from the intake and pressure from the valve cover side -- pushes the oil right through...whether the valve seal is good or not.

Tom Piper

 

In this C4/motor/head oil drain back issue as I'm not a mechanic. I do remember this very distinctly from when I had a 72 LT-1 C3 that I had to build a motor for. This info I'm almost positive was in the FSM. The subject was the info that the factory said about replacing the oil pump when you were rebuilding the motor. Use the OEM part from a chevy dealer or a suitable replacement pump with the same design criteria or you could have oil comsumption issues due to the "flooding" of the heads with oil. Look it's been since 1977 so I very well could have the place I got that info from wrong but I could swear that it was in the FSM set from Helm that I had for my C3. My FSM was ordered with the car by the orig owner as they were listed on the bill from the dealer along with the car and they were the bible to me as this was my very first motor that I tried to fix myself. I was a total nooob & my ASE friend that was teaching me got a kick out of me treating the FSM as the definitive word in all things!

I have not rebuilt a sb in along time & the lt-1 motor was the only one I ever did from the bare block to finished motor. I had a 88 chevy sb in my boat and when I wanted to "beef" it up I remember noticing that the design of the heads & cam valley, as it related to oil drain back, was unchanged to me eye anyway. Actually it could have been a bit better by I would never know!

This part I remember about the LT-1. It used a TRW HV/low pressure pump with the by-pass adjusted by TRW to chevy specs to produce the chevy desired oil pressure throught the operational rpm range. Hot @ idle: 20 - 35 psi, hot @ any rpm > 2K = 60-70 psi roughly. At those psi's the FSM(?) said that there would be anywhere from one qt to 3 qts in the "top end" of the motor, which they defined as a combined volume found by adding both heads and the cam valley.

The machinest that did the machine work on my LT-1 and my 88 350 was a car guy, into BB C2's. He agreed with the FSM and pointed me to several articles in Hot Rod(?) & SS & Drag Illustrated(?), reason for the ?'s is I'm 54 & don't remember exactly where but I remember reading the info. They said the same thing and I remember that in Smokey Y's book about sb chevy's the same warning was issued, along with some simple & effective fixes....they didn't solve the problem but made it less of an issue. Smokey said the solution is dry sump.

Anyway, back in the late 70's, which is when I did my LT-1, every machinest would offer for a fee to improve the drain back situation by enlarging the two holes in the heads and the holes in the valley and tell you to epoxy the valley and not to use a high pressure/high volume pump.They would tell you if you didn't go for any of the mods that you should stick to the OEM spec pump for street use. This stuff was done by one of the posters in this thread. I also remember that back in the late 80's that DART used their soloution to the problem as a selling point for their replacement heads.

I apologize for jumping in but this issue had so much deja vue for me.


Tom

 

Exactly what I had been thinking when I first read this thread.

Unless the blowby is "really" excessive, the scavanging pump will "eat" the crankcase pressure.

Under the same conditions -- more HP = more cylinder pressure = more blowby = more crankcase pressure.
So, if you want a higher horsepower engine, you need to have even less blowby than in a low horsepower engine. And, loose forged pistons and wider ring gaps are counter productive to this.
In the LT4, GM started using "positive twist" rings to help eliminate this problem.
The higher cylinder pressure of the LT4 caused the "positive twist" rings to flatten out at higher rpm to form a better ring-to-cylinder seal.
http://www.grandsportregistry.com/lt1vslt4.htm#RINGS


An important thing to keep in mind is, if the engine is sealed properly and there is crankcase pressure, the only way for that pressure to find an escape is up through the heads to the PCV system.
That flow up through the heads is counter productive to the oil flow down.

It would be interesting to provide a vent down in the top of the oil pan that released pressure into the rocker cover. But, it would probably "blow" too much oil to do any good.

So, the way I see it, to say the problem is AFR heads have a higher drain-back is the same as saying the penny you lost in the parking lot last month put your budget in the red -- it may have helped, but I'd really put my time into looking elsewhere.


Tom Piper

 

How about something like this to relieve the pressure in the crankcase?
I know they have headers that have a breather type valve on them and a SS line up to the valve covers to reduce pressure by haveing a vacuum on the engine.
http://www.theoldone.com/components/breather/
http://www.moroso.com/catalog/catego...?CatCode=13400
heres a Honda guys write up on it, and a few pages of good information, even thought it is a Honda
http://www.honda-tech.com/zerothread/1271191

 

I'm using a similar device I bought from greg @ blowerworks.

Underboost if i use a closed oil filler cap I pop it off from the crankcase pressure...

With a filter / breather I'm blowing oil out the breather I have a fine mist on the valve covers after a high spirited run.

I'm running a PCV that does ot leak back when under boost. I need to check a few hoses to see if i am seeing the oil in them that others are seeing...

Ironically the engine builder who built my engine felt a high volume pump was he way to go... As that seems to be standard fare in thier builds. My oil pressure is not excessive... it is about the same as the stock unit. Again yes I understand we are talking about moving "volume"...

Mo

 

So if too much oil is staying on top, in the meantime should we run an extra quart of oil?

 

I just put the head back on before I read this so I don't have any pics to show you.

I'm really stupified right now. I don't know what I should do.

a)I don't want to buy new AFR heads for $2700US plus they wouldn't fit my ported LT1 intake

b)I don't want to sell these ones knowing they have issues. I wouldn't feel right.

c) I don't want to starve my bottom end of oil and blow the short block

d) I don't want to risk killing the motor from another coolant leak from the same head.

The only reason I didn't bend a connecting rod is because I shut the engine off fast enough. When the car cooled off, I tried turning the motor by hand and it wouldn't budge. I had to remove the spark plugs to blow out all the coolant from my THIRD porosity related coolant leak in 500miles.

I have not had the car on a dyno yet but dam this car pulls hard even at half throttle so it appears the person that ported then for me (John@Muscle Machining) did an excellent job as well as the tune from pcmforless which really makes we want to keep them.

I guess I have the whole winter to figure it out.

 

Well, here is what I am planning on doing to Glens engine. I will get a set of push rods that has a .040" restricted oil hole in the push rod. This will effectively reduce the oil volume to the top end by between 50 and 75%. Basically this should reduce the oil passed to the top end so as if it has a stock pump again. While I am in there the engine builder recommended that I install a set of teflon valve stem seals. If it is a pump volume issue this should help it. The engine has two breathers, one on each valve cover plus a good operating PCV. I am sure that as Tom Piper mentioned it has something to do with crankcase pressure, but also if there is excessive amounts of oil is covering the valve spring pockets its just going to be much easier to have oil forced into the engine if the valve stem seals are submerged in oil. By reducing the volume to the head area with the new pushrods, in theory it should help. The other solution is to replace the pump which is a real PITA in a C4 with a canton road race pan. By the way don't attempt to use this type of push rod unless you are running roller rocker arms.