Oil leak collecting in converter cover
 

So i had the engine out last year, all gasket changed. BOP 1 piece oilpan gasket. BOP 2-piece viton rear main seal. did the tilt test with engine on cherry picker had it at about 45 dergee angle over nigth, also turned the crank a few times. came back next day, not a drop.

Fast forward a few weeks and and i notice a dime sized puddle under the car. I kinda got the wind knocked out of me seeing that and just used the car as regular the rest of the season with almost no oil use.

Today i had a round of spring prepp , changed brake fluild amongst other things and cleaned up the mess from the sump and back to transmission. i took off the converter cover expecting to see the flexplate smeard in oil and a wet crank flange. but to my suprise that area was dry. kinda at a loss. i ran the car on jackstands up to temp and shut it off. had a look under and not a drop from anywhere. Went home and made some food came back an hour later and there is the dime sized oil drop again. I think it is dripping from the center rubber nub on the oilpan, best i can figure..

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It sure doesn't look like the rear main seal is leaking. I've installed several of the BOP 2-piece seals on 389's and 400's with 100% success. And 12 to 15 years later, still leak free. Fingers crossed!

My engine leaks from that same location, but quite a bit more than a dime sized drip.

You may also want to check the back of the valve covers as well as the distributor. Leaks in that area can migrate downward through that same area.

I am almost tempted to use a long chisel and a hammer to gently knock the oilpan along the line of the rubber nubs to sligthly close the gap against the gasket.

I used that rubber seal once years ago, and never again!
I much prefer the good old cork seal with a good bead of gasket maker on each side and then let it set up for 12 hours and then trim off any ugly excess..

The only problem I have with doing it this way is when the time comes to take the pan off and to separate the two sides, and that’s the way it should be.

Try doing your chisel idea, but round over the nose of if pretty good on a bench grinder.

Then make multiple passes over the pan lip so as to just crimp it down little by little because those seals have a habit of pushing out with too much clamping pressure.

x2 on the 1/4" cork gaskets for the "U" seal on the pan. ive never used the 1 piece pan gasket but if it has rubber for the U seal its a crap shoot of sealing up, especially for the older 3 slot pans.

i have an aftermarket pan that uses the older 3 slot type seal, i had my machine shop assemble the short block since they offer such a good price & some type of warranty, but i do the rest of the assembly myself. after a fresh build of a stroker motor, i had a minor leak at the rear of the pan like yours, thought it was the rear main, the shop had me bring it back & replaced the rear main then reinstalled the pan using the same felrpo gasket i used, it leaked worse than the 1st time!

so i pulled the motor again & brung it back, they inspected the main seal & said it looked fine, so left it alone but this time i brought them a 1/4" cork gasket for the U channel in the pan after talking with mr Pbody & reading about it on here, they reinstalled the pan with the cork gasket & used ... ULTRA BLACK RTV... as was suggested. the pan has been drip free for about 7 years now with lots of street and drag strip use. if you pull the pan, use the cork gasket for the "U" explained here.

https://pontiacstreetperformance.com/psp/Sealit.html

if you want to try & hammer that area of the pan, i would use a 1/4" or 3/8" extension bit with a slightly rounded head before trying to use a sharp or even rounded over chisel. good luck whatever you do, oil leaks suck!

As mentioned, could be a valve cover or the distributor because it looks pretty dry under there.

I ended up cutting the nibs off my pan gasket to get it to center in the valley on the rear main cap. Otherwise the seal rode on the lip of the valley on the cap because the pan slots were stamped too close to the outside. It dropped off the center nib during the tip test for me.

I did some reading before installing the 1 piece oilpan gasket, followed the directions, lay down a bead of ultra black on the start of the bow. Where the cap meets the block on both sides, and a thin ultra black bead over the cap and one on top of the gasket where it meets the oil pan. But i can not for the life of me remeber if i lay the bead on the engine side of the nubs or the transmission side. I probably lay it on the transmission side, so oil can not escape out the back ( but it reaches the nubs and wicks down there)

are you saying you used sealer on the cap itself & where the U section meets the pan? ive never used the 1 piece gasket so not sure what instructions come with it, but the BOP website says to use sealer just on the corners where it meets the block & corners of timing cover to pan gasket, nothing about using it on the oil pan U gasket itself or top of seal to pan. i like ultra black & use it in many locations with excellent results, but BOP says to only use it in those specific locations, im not sure its designed for any rubber gaskets.

"Silicone/sealer is only recommended at the bend points of the timing cover and where the rear curve meets the block to account for any minor alignment discrepancies."

https://www.bopengineering.com/A_Pon..._Seals_1.shtml

the cork main cap gasket mentioned above does say to use a generous amount of ultra black.

I did add a thin bead of ultra black over the hump even though it was not mention in the instructions. I wanted the extra insurance, It was a thin bead as i did not want it to squeeze out and into the engine. In hind sigth i should have made the bead circle around all 3 nubs.

I really like this gasket. it has been spotless on every other place , not a drop at all. I hold BOP in high regard for the products they sell, and service is outstandig, really helps when you are overseas as i am.

i agree BOP has good products... but for these oil pans i think the thick cork gasket is best for the main cap. the rest of the pan gaskets dont have an issue like the rear U section, felpros i use on 3 of my cars are leak free on the side rails & front area to timing cover.

hope hammering the pan some helps or fixes it, but if you pull the pan to replace the gasket with the same BOP, i would consider not using RTV on the rubber section since they dont recommend it there. or call them to ask about using it there?

Yepp you are rigth, but i wil not pull the motor at this time. and dropping the the pan an inch to fiddle with it can make it worse.
For now i taped the drain hole on the converter cover from the inside to pass an upcomming inspection just to pass it without a visible leak, after that i can try to tap it down.

one time i made a dimensionally correct replica of the cork main cap gasket from 1/4 thick sheet silicone worked real well

remember when using silicone on cork or rubber gaskets until cured silicone acts like a lubricant grease its easy to effectually over torque and squeeze out gaskets or split and over crush them just using regularly proper torque

if you go the silicone route its best to use enough torque to get a good squeeze out ensuring full mating surface contact let it cure for a few days then apply final torque when the silicone is like rubber not grease

OP - hope you don’t mind me jumping in but didn’t want to start a new thread considering it’s same exact issue with my 64 LeMans - bought from a friend who had someone who else build the engine. It has the one-piece BOP RMS and the one piece BOP oil pan gasket. From my inspections the flywheel engine side is always dry so I assume the leak is at the pan to cap intersection. It sucks cause the engine is leak-free otherwise. No leaks from rear of valve covers or dizzy area. A few pics below with the undercarriage shot showing the amount of oil after a cruise.

I had the 1-piece BOP oil pan gasket and 1-piece rear main seal as well and I would get the tiniest drip from the center locating spike on the oil pan gasket exactly like the OP. I ended up snipping the rubber spike flush with the pan, cleaning with carb cleaner, then slathering a small amt of RTV on that area. It never leaked again.

I really like the idea of gently tapping the edge of the pan around the locator tab up to get a better compression of the gasket in that area.

Not at all :) same with me back of the heads are dry, same with distrubutor gasket, had a brigth led ligth on the cowl overhangeing the the transmisson bellhousing and rear of motor , everything looks dry there.

Now that sounds like a better solution then me potentially knocking my pan out of shape. i'll try that first the next time i have the car on jackstands or on a lift.

also just to mention, depending on what oil you are using, synthetics can leak or seep more than conventional oils from what i have found. if using synthetic consider trying a good regular oil to see if it leaks/seeps less.

if not using synthetic, consider trying an additive like lucas oil stabilizer, its not a stop leak & doesnt have any seal conditioners/swellers, but it does have a sticky or clinging property that i found to reduce leaks in my old daily driver jeep cherokee 4.0 with a bad & common rear main leak as well as pan & valve cover leaks on a 200k mile engine. lucas & conventional oil helped the leaking more than any other stop leak additives i tried.

Lucas oil stop leak , friend has had good results & no negative issues .

Well i did a short cut to pass inspection, and taped the converter drainhole just to pass inspection so i can legally start the season without fear of getting my licence plates clipped by officials.
I drove 45 minutes to the inspection facility. and Got 2 faults:
1: more than 40 % diffrence in applied brakingforce on the rear axle. i ordered 2 new wheelcylinders i i recon that wil cover that fault.
2: excessive oil leak! now i guess there is a lot of turbulent air in the converter cover blowing anything in there around as the inspector said everything between the engine and transmission was smeard in oil and it was dripping more than 2 drops during the 50 minutes of inspection. Man i do not have anyplace to lift and store the engine as the last shop we had has been sold and we can no longer rent it. all i got now is a 5% gradient dirt road lol. i need to do some experimenting with tips in this thread.


But 1 thing i would like to try: cut a thin layer of cork gasked over the rear main saddle with ligth RTV on both sides in adition to the onepice bop to increase clamping force on the hump.

Man that's how intensely they inspect the brakes there, Gez!

Before you order brake parts take a real close look at the condition of the backing plate pads where the shoes sit and on.
The bad side may be worn with ridges that make for more pedal pressure to be needed, and if they check out ok then do not forget to grease these pads.

Pan leak wise you really need to find a way to get the motor up and car out from under it.

I have used a big tree branch once to do such when I had no other way.

The pan needs to come fully off to do the job right as anyone who has had a leak the second time around will tell you.