# Oil leak: rear main or oil pan?



## Tbryan (Feb 17, 2016)

Hello, I would like to start off by thanking everyone that has posted on this form. I have been a member for a about a year now and haven’t had the need to post anything due to all of the good topics and answer out there. This particular issue that I’m having seems to be a common issue, but the way it is happening is stumping me.

I want to give a little back story to this before I dive in. The motor that is in my Lemans is a 428 out of a 69 GP which was done by the previous own. When I bought it, the motor was leaking from the Rear Main/Oil Pan area. My plan was to just pull the motor and replace the rear main with a 2pc. Viton Seal and the Preformed oil pan gasket from BOP (which I did). Long story short, once I was into the motor I found it need more than just a reseal. Flash forward 1 year later and here I am dealing with the same issue. So today I decided to see if I could figure it out. I put the car up on jack stands and add a fluorescent die to the oil to see if I could pin point the leak. When I first fired it up nothing was leaking. I let it run at idle for about 5 mins then bumped it a couple of time to 2500 RPM, still nothing. About 5 mins later the temp was stable at about 170 and then the drip started. It’s was pretty heavy and consistent. It seemed to be weeping around the oil pan and down the center “nipple” on the pan gasket. The dripping slowed down considerable after the motor was turned off. It stopped completely about 5 mins after the motor was turned off. I’m currently using Valvoline VR1 20W-50. Any insight or help would be greatly appreciated.

I also took a video of the area while the car was running. below is a link to it.

https://photos.google.com/share/AF1...?key=ZVZTYVlhY1FTbjVJYks0SFNsQTA2WVBJQmQyb2Rn

Thank you, 

Tyler


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## Lemans guy (Oct 14, 2014)

those one piece seals only go in facing one way.....they face different on the 3 inch main ones and the 3.25 main ones..

it can be confusing and did you put grease inside the lip of the seal? and the crank had the little cuts in it?....

just thinking with you some great internal engine guys here will chime in I am sure.....


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## Tbryan (Feb 17, 2016)

It's been almost a year since I assemble the motor, so I'm going off of long term memory. I do remember that there were cut marks in the crank and also there was some light pitting in the same area that my Machinist was not able to polish out. When I asked him about it he said it shouldn't be an issue. I remember that I assembled the seal just as the provided instructions said to do.


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## PontiacJim (Dec 29, 2012)

Watched the video. That is leaking pretty good. In my opinion, I don't think it is a pan seal as the car is not moving and oil is not sloshing to the rear of the pan, ie accelerating. There is no direct oil pressure, being applied to the rear seal, only oil, mist and blow bye pressure in the oil pan, will exert minimal pressure against the forward facing lip pushing against the lip forcing it to seal against the crank, and lubing the contact point, of the lip so wear is minimized. 

I used the 2 pc BOP seal on my previous 400CI and followed the directions and had no issues. However, there have been others on the forum who have had problems, so it seems sometimes hit and miss. The crank has the small grooves where the seal rides and these should be polished up a bit. Your machinist said that the pitting should not be a problem, but with the Viton seal it should be micropolished and the pitting might be a problem. It may not be a problem if you used one of the rope/graphite seals they now offer. I am not a machinist or expert on this, so depending as to where the pitting was on the crank, you have to trust your machinist.

As I recall, the seal came with a small "shim" that you set up against the seal end while it was in the block. One end of the seal was to be made flush with the block while the other end stuck out past the block. The shim was then placed next to the rear main seal stick out and you used this as a guide in trimming the seal so you had a slight/measured stick out of the seal. With the little bit of stick out, when the main cap was installed, this creates a little crush on the seal. The installation directions give you the amount of required stick out. Did you do this?

The seal only goes/works one way. Assume you fit it correctly as the installation guide is pretty straight forward on this one.

You also want to make sure the seal is lubed. If the seal was not lubed prior to dropping in the crank and torquing up the main cap, it can wear prematurely if dry. It has been recommended on another website to "never install the seal on a dry crank, oil it on the lip area and crank surface with wd40, on a q-tip to insure it won,t be damaged on start-up." One suggestion was to use a little vaseline.

If your PVC system is not working, rings are not sealing and blowby is being experienced, or if your engine does not have enough ventilation, ie valve cover breathers, the engines internal crank case pressure can potentially be a problem, in that the rear seal is designed to trap oil only under moderate crank case pressures. Some Pontiac engines seem to experience excessive crankcase pressures and need 2 valve cover breathers. I had an engine that would blow the dipstick out and push a little oil out it when I really wound it up. Added a second breather, one on each valve cover, and problem was solved. From what you stated, it could be the leak begins to develop once the engine's internal pressure builds? So you may want to look into this first before tearing into the engine. Not saying the seal isn't bad, but check this first.

So, just my thoughts on it. Not saying it isn't the oil pan either, but if it is either the pan gasket or rear main, the engine will have to come out. Also re-check all the pan bolts for correct torque. They can/do loosen up over time if you did not re-torque then after your rebuild. I also could not tell if you had the rear corner oil pan supports. Often they are discarded or not used when the engine gets rebuilt. You do need these: https://www.bopengineering.com/pontiac_replacement_parts.shtml


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## Poncho17 (Jul 5, 2017)

Sorry you are having the issue. 

If you have to take the motor out again and remove the oil pan I would recommend you go to your machinist and borrow the use of his surface plate, a flashlight and feeler gage. Look for flatness issues or an area that is not consistent with the others. The other thing to look for is if a oil pan bolt has torn the edge of the sheet-metal.


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## Tbryan (Feb 17, 2016)

I remember that I read the instructions about 4 times and I'm pretty sure I followed all the steps but there's a chance I might have missed something?

Yes the i do have oil pan reinforcement brackets installed on the pan. The gentleman at BOP recommended them when I bought the oil pan gasket.

Both of my valve covers have breathers and I also have a PVC valve that's brand new. I ran it again with the breathers removed and I pulled the dipstick out of the tube and I still had the same issue. 

It sounds like at this point taking out the engine is inevitable? . Before I start tearing into it I think I'm going to talk to my Machinist and see what his thoughts are too. Thanks everybody for the help and I'll keep you posted.


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