I am trying to track down an oil leak that only occurs when my newly rebuilt 455 is running.

Short test drives would result in about 1 teaspoon of oil in the bottom of the torque converter access cover. So I took it off.

Now short test drives result in oil dripping off the passenger side rear corner of the oil pan and some oil flung on the oil filter. I clean off everything after each trip and the areas that drip oil are consistant.

I have found that the oil filter is tight against the housing (no oil on top of the filter) and I just replaced the gasket between the oil filter housing and the block so no leaks there now. There are no drips or oil residue on the front face of the flywheel either.

Wouldn't a rear main leak cause drips straight down from the end of the crankshaft? Or is crankshaft rotation causing the leaking oil to fling to the right side (only)? That does not make sense to me. If the oil is being flung through rotation, I would think it would be everywhere.

I also have oil pressure from hell, so I am wondering if oil is just being pushed past my "supposed to be the cat's meow" BOP Viton seal and this will settle down one the motor is not so tight.

Sounds like the rear main to me, mine does the same thing. No viton seal though.

After going through the archives I am wondering if it is just the next weakest point in what seems to be a high crackcase pressure issue I have on this new engine.

Even with a PCV valve connected to the carb base (E-brock 1901 carb) I had seapage from underneath the 2 bolt heads for the vally pan and from valve cover breather caps before I installed baffled grommets. Then I blew out an oil pan gasket.

So I put a valve cover breather with a hose nipple on the passenger side and connected a hose to the air cleaner and put RTV around the valve cover grommets. Since then I have had no leaks up on top of the motor.

On the left valve cover I have a closed rubber "oil" plug. I may just put another baffled grommet in there with a breather.

What kind of oil pressure are you running at?

No numbers on the OEM '68 Rally gauges. 7/8's of the way on the gauge at start up; never below 3/4's of the gauge.

Would be interesting to find out with an oil test gage. After the motor is broken in, you may want to try a thinner oil like 5W30 or 5W20 with some anti-wear additives.

That sounds high. Your pressure sensor is on the filter correct? Maybe there is a restriction thus giving you a bad reading. The crankcase "air" pressure will probably not be affected. I think your real seal is just leaking. It's a [censored] those [censored] seals.

My builder was almost exclusively a racing motor builder. He put straight 30 weight Valvoline Racing Oil in it.

As I only had maybe 30 minutes of run time on it before I had to pull the engine back out to replace the oil pan gasket - I put the same 30 weight back in.

Yes, Stock oil pressure sensor for gauges off the oil filter housing with the correct 45 degree brass elbow fitting.

This is also with the 60 psi Melling oil pump. I did not make the mistake of installing the 80 psi 455 SD pump.

Good oil for break-in only. You should find out if he used a high volume oil pump. That in combo with the thick oil could be causing your problems.

I bought the pump myself - my wife used to work for a volume engine remanufacturing company. I'm almost positive it is the M54-DS.

What would be a good oil these days? Semi-synthetic? I have a roller camshaft setup so I don't have to worry about zinc so much.

I've always been running Mobile 1 10W30, but have been looking at their 15W50 due to the fact it has the anti-wear additives in it and my valvetrain is stock. Next oil change is a ways off though.

http://www.mobiloil.com/USA-English/MotorOil/Oils/Mobil_1_15W-50.aspx

Thanks. I just replaced the filter over the weekend when I replaced the gasket on the oil filter housing. I could not get the #$@%#& thing loose and I had to crush it to get it off.

So I might just drain and replace the oil with something lighter one of these upcoming weekends.

I worked on a GTO a while back with a similar problem. It had excessive crankcase pressure. He had Total Seal rings, and one of the things Total Seal tells you to do is restrict the PCV valve to .060 (or something like that) or you'll suck oil. Problem is, with the PCV restricted, the crankcase can't breathe.

Anyway, he restricted the PCV, as per instructions, using an old Quadrajet .065 jet in the hose. After a short drive and a blast through the gears, the rear main seal was leaking. We cleaned everything up, I removed the PCV restriction, and the problem went away....

But the other thing I to his car is what I did to mine.

Years ago, my setup was stock, with an oil cap on the driver's side and a vent tube to the Ram Air pan on the other. After a blast down the 1/4 mile, the dipstick would always be about 1/2" out of the tube. Not enough ventilation to relieve the pressure at 6000 rpm.

I now run double breathers (on stock valve covers), both breathers have 5/8" nipples. I ran two 5/8" heater hoses to the back of the air cleaner, and into a T (easily found at any hardware store for a couple bucks), then the T goes into the back of the air cleaner housing. Now under full throttle, any crankcase pressure vented using TWO breathers. At part or full throttle, the carb is pulling crankcase fumes through the T in the back of the housing.

Basically the same system as the factory did, but instead of a vent tube on the passenger side going to the air cleaner, there are two vents.

If it leaks, doesnt matter what type of oil. Its still gon'a leak.

My rear seal leaked a few drops but enough to wet the tranny over time for the first few years 5000 miles...seems to have stopped now though so must have finally swelled up.

As I mentioned in another thread, if you have a rope rear main, one of those bottled products by Bar's Leaks (or similar) that claims to "fix rear main seals" do indeed work. They simply swell the rope seal, and do not affect the oiling system.

The rear main is always a thorn in the side of proud Pontiac owners. But rear main seals rarely leaked on a factory assembled, never-been-apart engine. The leaks started occurring when rebuilders did not install the rope seals correctly, and then of course later there were all sorts of whiz-bang rubber/silicone/molded products supposed to free up 5 hp, and they leaked like crazy.

A Buick friend of mine calls a stain on his driveway "The Mark Of Pontiac" (reference to the Mark Of Excellence) because his friend's 71 GTO always leaves a dime-sized spot of oil on his driveway when he visits.

I replaced the rear seal in my 428 with a Viton seal, it was good for a couple thousand miles then started to leak more and more. Apparently some of the blocks had seal grooves that were non-concentric and the viton two piece seal will not conform to the shape and leak. A 'Best Gasket' graphite rope seal may solve the problem.

IMO the ONLY seal that won't leak on a Pontiac block is the Viton BOP seal. HOWEVER, there are a few tricks to installing them CORRECTLY. I had our mechanic friend install mine in the Bird, with the motor in the engine bay, both motor mount bolts removed and the engine lifted just enough to remove the pan.

Once that BOP seal was installed, not a drop since! The rope seals on the market are not the same as they were years ago. There is something different about them and they all leak eventually...

I have a BOP rear main seal installed. One of the reasons why this issue is frustrating.

I have been mulling through threads on this subject on this site and PY along with remembering exactly what I was doing before and after finding this leak.

I had made a couple of local road trips at low speeds - nothing over 35 mph. No leaks. It's not until I started longer shakedown cruises over 40 mph that I would have leaks. I have a 3.55 rear, so those later rides were pushing 3000 RPM.

I am going to try a couple of things over the next few days before I consider changing out the 30 weight oil. I am going to start it up again in the garage and let it warm up and idle without going much about 2000 RPM and see if it leaks.

I should have enough breathers and grommets from my previous experiments to be able to at least set up one valve cover breather plumbed to the air cleaner (what I have now) and just a 2nd open breather on the other valve cover. The chrome air cleaner I have did have two breather hose nipples on it, I just blocked one of them off. I also have another breather with a hose nipple, it's just that that nipple was a bit large for the 5/8's hose I was using.

From what I've read the 3inch main blocks were machined well but some of the 3.25 inch blocks had trouble in the rear seal grooves. The grooves were either not true/ round or they were not on the same centerline as the crank. The rope seals would fill the discrepancy but the more rigid lip style seals cannot fill the void and even a correctly installed one may leak. Mine did.

I read about that as well.

However, tonight I changed out the hard rubber plug in my left valve cover for the standard breather I had ordered with the valve covers. I fired the car up and idled it for a good 10 minutes in the garage (did not exceed 2000 RPM). No Leaks.

Looks like I have excessive crankcase pressure which, according to the PY archives, is not unusual for a newly rebuilt high HP Pontiac motors.

Next will be another test run with speeds above 40. If this breather changeout does not work, I will need to get another breather with a nipple and run a 2nd hose to the air cleaner. That should vent the crankcase enough to keep me from forcing oil past my rear main seal.

I'll agree to that. I don't see how oil pressure has any effect on crankcase pressure.

Yes, I read that over at PY too and the explanation made sense. The oil pump pressurizes the oil passages, NOT the internal atmosphere of the block. Excessive blow-by from new rings in a tightly rebuilt block pressurizes the crankcase until they seat. Some builders on the PY threads said that could be as much as 1000 miles.

And then I remembered my previous '80 Turbo T/A where the factory requirements for oil had to be strictly adhered to to avoid problems.

The Pontiac oil mandate for the 301 Turbo Motor?

Straight 30 weight all year long in temperate areas.

Should be the other way around. Crankcase pressure will have an effect on oil pressure, at least with respect to atmospheric pressure. Since one side of the oil seal is at atmospheric, it can impact the amount of oil that leaks out of the block. I would suspect it is not a noticeable affect unless crankcase pressure gets real high.

Kinda sorta. Yes, increased crankcase pressure is going to push oil out seals and gaskets. In my case it is RPM related.

But crankcase pressure is not going to affect the oil pressure we measure with our instruments just downstream from the oil pump.

I read yesterday that some semi-professional Pontiac racers are having to install vacuum pumps on their engines to keep from sucking oil into their PVC or breather systems. That's how high their crankcase pressure gets.

Not sure how much I can add to this thread, but if I recall, when I put the BOP Viton rear main in my engine, I remember having to drive out some anti rotation pins from the cap (originally used to keep the rope seal from spinning) and silicone the holes. Was that type of prep work done? Also, required fitment with an exacto knife to get exact length. It wasn't just drop in the new rear main and go.

Do they use the vacuum pumps on naturally aspirated engines or just supercharged?

Some racers reported needing to use vacuum pumps on both NA and superchaged motors depending on how nasty the NA motors were. There was a very long posting over at PY about PCV systems (that was in the title) that was really interesting. If I remember right, it was from 2001 or so.

While this was my builders first attempt at a BOP seal, he was well versed in modifying the Caddy neoprene seal for Pontiac motors before that. I made sure he had the instructions. As his engines were always the top finishers at all the local races and all the car guys in town raved about him, I pretty confident he did a good job putting the seal in.

Here's the PY post on PCV's:

http://forums.performanceyears.com/forums/showthread.php?t=453803&highlight=PCV

Salmon38, thanks for the PY post. Good read.
Al.

And it looks like the 2nd breather in the valve covers fixed my problem. Drove the same circuit this evening that previously would result in what thought was a rear main seal leak.

Nada tonight.

Good to hear! That's what I had posted earlier, dual breathers solved my problem, and I made my own setup using a T in back of the Ram Air pan. Just a note, the breathers with those black 'loose fibers' inside are much better than the ones that use foam.

Those rear main seal leaks are sometimes a bear to find. When the crankcase pressure is high, the oil gets pushed out the rear seal, and the flywheel flings it over the starter, and the oil filter housing. By the time you jack up the car to look, it appears the oil filter housing, or the oil filter itself, was leaking.

I may have spoken a bit too early. There was just one small drip on the corner of the oil pan this morning. So I will be going to your 2 breather connected to the air cleaner setup.

The air cleaner that I am using (aftermarket on the car when I bought it) has 2 hose nipples on the bottom - I just blanked one out previously.

I found some technical doc on the net that supports the "high pressure" in the crankcase issue. Have a look...

Engine Breathing Systems
Thread about too much oil pressure
Thread about PVC valves

for what it's worth, seals are "directional" They have a hydro dynamic feature which pumps oil/air inward thus keeping the oil inside the pan.

If a seal is put in backwards, it will pump oil out of the crankcase, usually at a high rate, which does not sound like that is the case here.

Also, hope there was not an excessive amount of RTV used at the joint. when compressed wet, it can ooze everywhere (into the groove for the seal) and possibly disrupt the compression of the seal in the groove or keep the ears open. Rubber is not compressible, only displaceable. If the groove volume is smaller than the volume of the seal and RTV amount combined, you will not get full compression if that makes sense? I am referring to the ends of the seal contacting (top & bottom) with the correct pressure.

Just my .02 cents.