Rear main leak. Oil pressure too high?

Hi,

As the title suggests, we have a rear main leak in our 545BBF. We rebuilt the motor a couple of months ago and it has started leaking from the rear main. It is enough to spray oil mist inside the car (tube chassis Ford coupe, glide running inside, inspection opening in the bell near drivers foot). It is running around 75psi oil pressure. Rather than a damaged rear seal could the problem be too much oil pressure forcing oil past the seal? If yes, any suggestions on what to do?

Thanks in advance.

Ian

the question is did you put it in right? most don't know how...

75 psi should not be an issue.

Do you have a good evap system?

The only installation issue I can think of would be too much crush. I haven't been in the habit of checking rear main crush in any of my previous engines but have read recently that too much crush can lead to leaks. Prior to the rebuild it was dry so it is either too much crush or oil pressure. My 351C runs happily all day at 75psi but maybe there is some nuance with the BBF that I am unaware of?  I'm hoping I can find the problem and that it's not going to require the engine to come out.

We run an Moroso vacupan system.

Ian

If the issue was an evac issue oil would be coming out of the dipstick tube and trying to push the intake manifold end gaskets out.

"spray" is the word I'm keying in on. Most of the usual main seal issues are more like a drip.

There are some drips, but the issue is that it is misting oil from the bell into the car. It's enough to hit the door but very fine mist. We can't race with it like that! I seems to be under pressure and being flung by the flex plate. I haven't seen anything like it before. The only other thing I can think of is a gallery plug failure but I think that is unlikely.

sounds like someone didn't stagger the rear main or put it in backwards.....there is no direct pressure to the rear main seal it has a void in the lower main cap which lets it flow out to the pan...

It's definitely staggered. Maybe I had a moment and put it in backwards. Would be a first if that is it. Maybe it tore on startup? Whatever the situation, it sounds like I need to open it up and replace the seal.

Thanks for the help Lem and others.

Ian

Lanxy check the end of the seal I have seen them with little titties on them and they won't seal against each other...

Thanks. Will do.

the Coug wrote:sounds like someone didn't stagger the rear main or put it in backwards.....there is no direct pressure to the rear main seal it has a void in the lower main cap which lets it flow out to the pan...

I've never figured out how "staggering" the ends of the seal could make any difference what so ever in how the seal functions, please explain.....

You lube it up good Ian on assembly ? I've checked the crush on a few since reading it here , the blocks had been line honed but the crush still was ok .

Yes Greg.  did all the usual things.  I use engine oil on the rear main.  Only issue may be that between installing the crank and start up was a couple of weeks.  I'm going to have to pull the engine and put it on a stand to find whats wrong. I too wasnt aware of the crush issue until recently (when this problem first arose and I started researching).

DaveMcLain wrote:

the Coug wrote:sounds like someone didn't stagger the rear main or put it in backwards.....there is no direct pressure to the rear main seal it has a void in the lower main cap which lets it flow out to the pan...

I've never figured out how "staggering" the ends of the seal could make any difference what so ever in how the seal functions, please explain.....

X2 I never staggered a seal on any of the 302's , 351w's or 460's and never had them leak.

Sounds like it's either backwards, worn out seal or face on the crank, or to much pressure in the crank case? I've had some issues with eagle and scat cranks leaking in the past, guessing it was a sizing issue on those?

Oil pressure wouldn't be a problem at 75#. I have ran much more than that before with no problems.

dfree383 wrote:Sounds like it's either backwards, worn out seal or face on the crank, or to much pressure in the crank case? I've had some issues with eagle and scat cranks leaking in the past, guessing it was a sizing issue on those?

Years ago, my machinist showed me a new import BBC crank. When he put it in the v blocks and spun it with a dial indicator on all the mains, it was fine, but when he put the dial indicator where the seal rides, it bounced up and down. I can't remember how or if he fixed it.

DaveMcLain wrote:

the Coug wrote:sounds like someone didn't stagger the rear main or put it in backwards.....there is no direct pressure to the rear main seal it has a void in the lower main cap which lets it flow out to the pan...

I've never figured out how "staggering" the ends of the seal could make any difference what so ever in how the seal functions, please explain.....

I guess you have never had any crush on the seal huh? I have seen where the seal has spread when you put the main cap on and the ends get under the main cap and kept from mating completely.... I have staggered the seal 1/8 or more to keep the edges from flaring out and crushing up under the main cap ...


also inxy check to make sure the groves on the seal area are cut in the right direction I have seen them cut backwards to where when the crank rotates the push any oil to the seal area...

the Coug wrote:

DaveMcLain wrote:

the Coug wrote:sounds like someone didn't stagger the rear main or put it in backwards.....there is no direct pressure to the rear main seal it has a void in the lower main cap which lets it flow out to the pan...

I've never figured out how "staggering" the ends of the seal could make any difference what so ever in how the seal functions, please explain.....

I guess you have never had any crush on the seal huh? I have seen where the seal has spread when you put the main cap on and the ends get under the main cap and kept from mating completely.... I have staggered the seal 1/8 or more to keep the edges from flaring out and crushing up under the main cap ...


also inxy check to make sure the groves on the seal area are cut in the right direction I have seen them cut backwards to where when the crank rotates the push any oil to the seal area...

X2
Like Randy Said I like to stagger mine also so the ends are in the block and rear main cap my Dad told me about staggering the rear main seal back when I rebuilt my 1st engine many years ago. He said I will have less chance of a rear main leaks this way and that why I do mine that way.

Jim I have seen what they do on main caps and when you butt the flush with the cap they seem to mushroom out and under the main cap, when you stagger the slightly they don't mushroom.

JMHO, but maybe check for a lose oil galley plug or even a small crack in the boss where they screw in.

Gotta be backwards or incorrect part. 80 psi and no evac on the old 514....nary a drop in years.

the Coug wrote:Jim I have seen what they do on main caps and when you butt the flush with the cap they seem to mushroom out and under the main cap, when you stagger the slightly they don't mushroom.

Let's see a picture of this phenomenon that you're describing, I've never seen such a think and I still say that messing around with staggering the ends of the seal makes zero difference.