Rear main seal..........yep, still leaks
 

Had a post of mine on 10-21-23 about my rms seal leak..........alot of good answers on what might be the problem..........so you dont have to read the thread, tried the best gasket seal, then the one piece bop seal, no idea on what was used on the 1st rebuild.

Im just trying to understand this a little better..............is it possible about some machining defect, or block issue why these gaskets dont seem to work one way or the other.

Pics show after running about 30 or so miles, about 5 drips after running, i clean them up.............couple hrs later another 4-5............this was from driving on Last sunday............monday about the same amount of drips...........tue on 1 drip as in pic...............wed , back to the 3-5 drips.......

My question, i understand it will drip while driving, but why does it keep dripping three days later while the motor isnt running.............

Im thinking maybe its something with this 455 block, and maybe not with the gaskets themselves...............any thoughts on this.

Big question for you guys with leaks.............this seem about normal for you also.............as of right now, i have 330 miles this year, and the dipstick is still reading full.............maybe im not losing all that much oil, lol..........who knows.

Not sure what im gonna do in the future, but thinking 3 strikes im out with this block ...............

Rich

forgot a pic................like i said, 4-5 drips , then check about 5 hrs later, the same............then check again the next day.............only one drip like in the pic..............then a few hrs later back to the 4-5 drips...............im gonna have to live with this because im not pulling the motor again.

I just find this strange with nothing running why all the drips...............the reason the drips seems all over the place was i drilled a few holes in the inspection cover, didnt want that getting on my clutch.

The drip in back im assuming is flying on the trans and dripping later.

Like i said, about 330 miles so far and dipstick still reads full...........im assuming i should get 600-800 miles before adding a qt............maybe thats gonna be the best i can do..........lol

Rich

You're 100% positive it's the rear main seal and not the pan gasket? The rear corners of the pan as well as the half moon cutout below the rear main is notorious for leaking. The factory pan doesn't help this any because there's no ridge to keep oil from climbing the rear wall up towards both the rear main seal and the pan gasket. This is why it continues to leak. Even moderate throttle application and moderate acceleration will see a wall of oil climb the back wall of the pan and seep into the gasket area.

I had the same issue with my 455 until I replaced the pan. It would drip, sometimes for days from a spot that led me to believe it was a rear main leak. When I had the engine out to replace the pan, the rear main was dry, but it was leaking from both rear corners of the pan and significantly around the half moon cutout for the rear main cap.

I opted for the 1 piece BOP pan gasket and spent a good amount of time with a ball peen hammer making sure the pan was flat. Even though the pan was new, the rear corners needed some massaging to get them flat and several of the bolt holes were concave and needed flattening. I then used a small dab of gray RTV at the front corners where the pan meets the timing cover, at the corners of the rear main cap and a light smear on both the rear main cap and that portion of the pan itself. I let the RTV set for a couple minutes, then bolted the pan up, making sure the areas that received a dab of RTV had a tiny pit smoosh out from the corners, indicating it had sealed those angles.

In my case, the engine went back in the car a couple days later, but I would wait a minimum of 24 hours to let the RTV set before putting any oil in the pan.

Also, make sure you do not over tighten the pan. It can be tempting to wrench down on this stuff in hopes of sealing it, but that bends the pan and actually pulls the rails off of the gasket surface, creating areas that can leak.

None of this matters of course if it is actually the rear main leaking. My point was just to illustrate that leaks on the pan itself can present as a rear main leak. Even leaks at the front of the pan. Because the engine is typically angled downward, plus the direction the car travels, leaks near the timing cover can travel along the crevice between the pan and engine towards the back wall of the engine where it will then creep down the back of the pan, around the transmission bellhousing, on to the starter and cause drips in those locations. You can spend a lot of time chasing oil leaks at the back of the engine when they are actually at the front!

I tried to fix mines with the two piece unit begrudgingly...still leaks of course

I've learned to live with it as I have never had a non-leaky pontiac 😑

I paid an experienced friend to both build and deal with the machine shop that was tasked with machining my 421.

He had already done several with the latest one-piece BOP Engineering seal and knocked it out of the park, he is the go-to guy in his Pontiac club for engine building.

150 miles later zero oil or coolant leaks. :thumbup:

We’ll see how it goes from here. :)

First picture installation of the crank and BOP seal by himself using an engine hoist. Second pic static testing of the main seal and oil pan sealing at the rear. Third pic on the run stand for break in and lastly my friend and his son unbolting the engine from the stand so I could bring it home.

Jason, you bring up alot of good points..............im not 100 % sure its the rear main, just going by the oil is all over the front of the flywheel and on the bottom of the inspection plate................the guy did a smoke test on the motor, said the only leak was at the front of the pan, which i guess 2 inches of silicone must have stopped the leak..........lol

Guess what im asking is what im showing in the pics about normal for you guys with some leaking issues................i guess i can live with this, not happy about it, but way too old to go messing around with this for the 4th time.

And whether im right or wrong about the rms vs the oil pan, the motor has to come out again anyways...............not sure what im gonna do, but so far the motor is running great, except for the leakage.

Rich

None of this matters of course if it is actually the rear main leaking. My point was just to illustrate that leaks on the pan itself can present as a rear main leak. Even leaks at the front of the pan. Because the engine is typically angled downward, plus the direction the car travels, leaks near the timing cover can travel along the crevice between the pan and engine towards the back wall of the engine where it will then creep down the back of the pan, around the transmission bellhousing, on to the starter and cause drips in those locations. You can spend a lot of time chasing oil leaks at the back of the engine when they are actually at the front!

Jason, just reread this again....................in the front of the pan is where the builder put the excessive amout ouf silicone on my pan.............makes you wonder where the problem is in the first place...............not sure what im gonna do except is watch whats going on..............hopefully this all works out ok

Rich

Check here too if you pull it back out. https://forums.maxperformanceinc.com...ight=rear+main

If it’s a a couple drips like you are seeing currently, I’m not certain I’d want to pull the engine to meaningful work on the pan. I’d probably invest in a decent drip tray instead.

Mine used to drip about double that amount. I lived with it for years, then took care of the problem when I had to yank the engine for something else.

Jason................this is the finest dirp tray money can buy..........lol, i dont even know where i got this from..................im gonna leave it like this for awhile..............thanks for the help, sometimes i worry about way too much stuff to worry about.

Rich

Maybe it's not the RMS leaking. Occasionally I've come across engine blocks that have porosity holes. I posted a picture of a block we recently repaired that looked like a seal leak. The best seal on this planet would never have stopped the leak. It acted just like a bad RMS, the oil ran down the pan and dripped off the lowest part.

The picture shows the rear of the block. The large hole is the other end of the RH side rear main cap dowel pin hole. The hole that was leaking is circled.

The amount you’re showing would bother me enough to fix it.

Have you tried UV dye to see where the leak is actually coming from?

I tried that last year, the black lite didnt seem to work all that well, will try again this year..........

Wanted to say thanks for everyones help............good points, thinking if i go about fixing this, im gonna try a different block, this is the 3rd time with this 455 and im losing confidence fast...........maybe nothing wrong with the seals, could be the block for all i know.

I guess what im having a hard time wrapping my head around, i understand it would drip while driving some, and a little when shutting down, but 2-3 days later without it running, i mean where is that comming from.........lol

Im not getting any younger, 73 this month, not sure i want to mess with taking this motor out again............have a great day guys.

Rich

On a lighter note, my mother who is 94 says, let me try putting that rear main in..................im thinking why not........lol

What a Mom!

:)

I'd also check the rear gasket area of the pan.
Was a cork gasket used on the pan 'half moon' section or rubber?

:confused:

Pontiac V-8 is among the most difficult engines period to get 100% leak free at the rear pan/main seal area. I consider myself pretty skilled and I am probably 50-60% absolutely leak free in that area. I mean not a drop of oil after lots of miles and hard driving. The other half do show some signs of weeping or an occasional drip or two on the ground when parked. There are just so many factors conspiring to make them leakers back there. 1. Not near enough fasteners holding that giant oil pan on. 2. A huge expanse of very thin sheet metal over the main cap area with no support and three different attempts to seal it, cork, and two lousy rubber seals. 3. The rear main housing bore is a complex shape and the cut is not accurate for size or diameter or centerline. 4. None of #3 is particularly important when using a rope seal because it will conform, but the rope itself has issues as we know. 5. Using the aftermarket seals is always worth a try because they are a dynamic seal. 6. The aftermarket seals have issues when the main cap and block groove are lousy though as mentioned. They are not very forgiving on the OD dimension and an out of round bore. So overall, it's not one of Pontiac's most endearing design features. Much like a Harley engine, Pontiac's like to mark their territory.

I know this is a longshot and probably not the issue, but what appeared to be a RMS leak on my newly rebuilt engine ending up being an oil filter housing gasket leak that evidently leaked and traveled south. Doesn't entirely make sense to me, but that's what the shop said and now has not leaked.

I think you really need to confirm where the leak is coming from. On my previous build I had a leaky pan, a leaky two piece rear main AND a leaky oil filter adapter due to a crack. It was a mess under there. Oil can also leak down from the valve cover gaskets or distributor. Lots of places it could be coming from besides the rear main. Try the UV dye again or pick up a smoke machine.

As a band aid, if you really don't want to pull the engine, you could try a Wagner dual flow PCV. It obviously won't help if it leaks while sitting, but it may minimize leaks exacerbated by crankcase pressure at run time.

Wow...mom looks great for 94. You're both lucky to have good genes.

[QUOTE=johnta1;6507724]What a Mom!

:)

I'd also check the rear gasket area of the pan.
Was a cork gasket used on the pan 'half moon' section or rubber?

Thanks John, for the oil pan i used the one piece from bop, was gonna cut the part off that went over the crank and use a piece of cork for the cap, thought this would work as is.

Im gonna take Verdoro 68 advice, will try to dye and blacklite and see if i can get it right this time..............on the smoke test the builder said he did this and the only place it leaked smoke was on the front of the oil pan..........there he threw enough silicone on it..........i can run my finger up where he did the work, still get a little oil on my finger...........so much for the smoke test.

Dont know if its true or not...........read a few reports about the seal not leaking to let smoke by, but oil will leak, so not sure on that deal.

So far my plan is drive the car this summer, hopefully i can buy a motor somewhat like i have now..............just dont feel confident using this 455 again.

At least one good thing came out of this, i had the motor re-ringed, at least im not blowing smoke all over the place.............just dripping it.

Rich

You could run a vacuum pump. Its bolt on.
A lot harder for a engine to leak with negative pressure in the crankcase.
My last engine, no leaks. Well sort of. I had a leak from a valve cover due to those inexpensive top bolt fabricated valve covers. They have a lip that holds oil on the bottom rail.
Cured it with a little Permatex #2 along that bottom rail.
All my engines have leaked a little until now with the V pump.

It was easier for me to smoke test the engine on the stand than in the car, but it worked in the car just fine. I also had a giant gaping hole in the rear main so there was plenty of room for the smoke to escape. Might be harder to see with smaller leaks. You should definitely take the inspection cover off, too.

I have some dye in my T/A right now trying to chase a leak. It takes a little more detective work than the smoke tester. Clean the underside off of any oil before you put the dye in and check underneath it frequently after a few short drives. If you dump the dye in and drive around a lot it will be harder to chase the origin of the leak since the oil gets blown around.

After my second rope rear main failed, I was looking at the machine work on my block (it was line bored) and the straightness of the crank. I never got a definitive answer on what ate them up, but I'm fairly certain it was the serrations on Eagle crank. I had the crank and serrations polished and carefully installed the BOP. Fortunately I've been leak free since (knock on wood), however I do get a tiny bit of oil residue around the rear main after a few hundred miles. I've been watching it like a hawk. The BOP seals take a bit of work to install, but they have a reasonable amount of tolerance built into them if you fit them to the block correctly. I think it's -/+ .005. I guess my point is I think your block has to be pretty bad for the seal not to work.

Thanks for that info Ken...............i think i got to get a better black lite other than the cheaper i have, its like a little pen lite deal, i have the stock crank in the car, not 100 sure but i think the block was line bored somewhere along the line............motor was done in 2007, then re-done in 2010............cant really complain after the two rebuilds it never leaked on the ground although the inspection cover always had oil in it............had the motor re-ring last year, this is the first time i had oil leaking on the floor though.

This has been really frustrating for me.............i pay good money for top notch parts and get half ass results..............not sure which way im gonna go with this, but i do appreciate all the help i get from you guys.

FYI............the reason i had the motor re-done in 2010 was due to very excessive oil consumption..................last year i was blowing so much smoke out the rear, i got it re-ringed

Other than that the motor runs great, never let me down in 20 some years..................just gotta come up with some plan.

Rich

Thanks for that info Ken...............i think i got to get a better black lite other than the cheaper i have, its like a little pen lite deal, i have the stock crank in the car, not 100 sure but i think the block was line bored somewhere along the line............motor was done in 2007, then re-done in 2010............cant really complain after the two rebuilds it never leaked on the ground although the inspection cover always had oil in it............had the motor re-ring last year, this is the first time i had oil leaking on the floor though.

This has been really frustrating for me.............i pay good money for top notch parts and get half ass results..............not sure which way im gonna go with this, but i do appreciate all the help i get from you guys.

FYI............the reason i had the motor re-done in 2010 was due to very excessive oil consumption..................last year i was blowing so much smoke out the rear, i got it re-ringed

Other than that the motor runs great, never let me down in 20 some years..................just gotta come up with some plan.

Rich

Maybe there’s someone in your area who can properly install the main seal for you, and handle the short block assembly as well. Even if you have to drive all day to drop it off with someone who’s calm and collected when it comes to these sort of things it’ll be worth it.

This would be after you have the block inspected for possible casting porosity and concentricity of the main seal groove to the main bearing bore. Someone who’s very familiar with precision measurement needs to do the inspection, there are instances where the seal groove is too far off to use the BOP one piece seal.

I paid someone who was more experienced, better equipped and just plain better at engine building than I ever will be and it was worth every penny.

[QUOTE=gtorich;6507780]Hi Rich. Sorry to hear youre still dealing with the leak, we discussed this last year on emails & I still say its the pan "U" gasket causing the drips. The thick cork gasket and ultra black will stop that if the leak is from that area.

I had the same type of leak on my 467 stroker build, I had my local shop build the bottom end & install the BOP 2 piece seal, I installed the rest of the engine including the oil pan, used the OEM rubber "U" seal, had leaks like yours right away & looked like it was from the rear main, I cleaned it with brake clean then let idle for a couple minutes & it would drip again, cleaned it & let sit overnight & had drips. I pulled the engine & brought back to shop for new RMS, had them install the pan this time, got home & it leaked way worse, like a 5" spot on the ground instead of a few drips, (I installed the pan gasket better the 1st time!)

So pulled it out again & brung back to shop, they said the prev RMS looked fine but this time I had them use the cork gasket & ultra black sealer like Mr P-body suggested and I sent you the link of how to do it, been mentioned on here before too, got a free dyno run to verify no leaks & did a few pulls just to see what HP was... was leak free this time & still is drip free after 8-9 years. It will "seep" a bit after months of driving but just wipes off with no drips or leaks.

My advice is the same as last year, use the cork gasket for the rear U seal, & consider a standard felpro gasket instead of the 1 piece, & be sure to use the rear corner tabs. As a band aid you can try a good sealer like ATP305 or even bars rear main sealer along with a high mileage oil to see if that helps.

Best of luck!

Just a side note concerning using a smoke machine for leak testing. I have 100% success finding a leak using them. But you need to smoke test the engine without oil in the pan. It can have a quart or so in there, but not full of oil. If the leak path is submerged, the smoke, under the very low pressure can't push the oil out of the way and smoke out.

My advice is the same as last year, use the cork gasket for the rear U seal, & consider a standard felpro gasket instead of the 1 piece, & be sure to use the rear corner tabs. As a band aid you can try a good sealer like ATP305 or even bars rear main sealer along with a high mileage oil to see if that helps.

I remember this well from last year my friend.................lol...........i thought it was fixing itself, looked good for awhile but now its getting worse..........couple pics for you here but hard to see anything, i cleaned up stuff today, hard to believe with oil everywhere except the rear bumper.........ok not that bad.

Hard to tell from the pics but i can see where i put some right stuff along the edges of the bop gasket, just didnt use the cork gasket in the grove..........seems im getting a little oil in the bellhousing by the clutch, wasnt there last year.

Was thinking today, just sell the car at a loss and be done with it...............but i have 25 yrs with it, just hard to let go, but this pulling motor for the 4th time is really getting old. and im still worried its gonna be the same old song and dance, leaking oil.

As per Barts note, to find someone to put this together with the rms.............im not doing this on my own, these are shops doing it.

Im gonna drive the car this summer and hope for the best....................hoping a motor will pop up on the forum that isnt insane compression level................tried a couple times with bulters, but everytime i call they say no more motors for this year.............

I guess im really getting old, i read, just pull it, no big deal..............well im not thinking along those lines.............lol

Well anyways, few pics, not sure you can tell anything one way or the other.

Forgot to mention............really couldnt tell if any oil was on the front of the flywheel...........looked liked there might have been some, but i figure it got flinged off..............will post a pic of where i drilled a few holes in the inspection plate, thought this might be better than oil staying in by the clutch area...........thinking this might be worse for driving as i said oil is all over my trans and exhaust from driving.

Rich

Awesome mother!

My mother was always encouraging me with auto and other related projects when I was young, had no problem grabbing tools, getting dirty and enjoyed the process along with me. She helped me carefully remove and tag the entire interior out of the '59 about 12 years ago.

Thanks for that post.................ma is also pretty strong for her age..........lol

Rich

Wow, she is amazing.

I fought a leak for most of last year after getting my engine back from a machine shop that was strictly a rip-off joint.
5 times I pulled the motor and resealed the oil pan, believing it was the cause and not the main seal.
Turned out the shop lost all it's staff and was conning everyone that they were still in business...but that's another story...

By the 5th time, I changed my strategy and figured out a way to test the rear main seal for leaks.
After cleaning up all the oil sprayed around by the flywheel, I took some 1" strips of paper towel, folded them over a 1" paint scraper and pushed them up behind the flywheel flange.
Then I used my shop vac to push air into the oil fill hole on the rocker cover for 30 seconds. This slightly pressurized the crankcase.
When I removed the paper towel strips, they had oil on them, confirming it was the rear main seal leaking.
Turned out the con shop never read the instructions for the 2-piece vitron seal, and never sealed the anti-rotation holes with silicone prior to installing the seal.
They also never replaced the rings that they charged me for, and over-torqued the main caps ruining the bearings and the caps. I can't even be sure they replaced the bearings as they did not return any used parts.

For the oil pan I used a new Milodon 7 quart pan and test fitted it using a feeler gauge all around to get it just right.
Then I used Butler's one-piece gasket, but removed the rubber 3-prong section.
Instead I made a 1" wide, 1/4" thick piece of rubberized cork out of 2 pieces 1/8" thick cork gasket. (Typical Felpro gasket pack)
I siliconed the 2 pieces together, and taped it down over my bench grinder motor , so it will set in a curve to match the pan and rear cap.
Once dry it was just a matter of trimming to fit, a bit of silicone where it meets the Butler gasket, a bit more to seal the slots in the pan and no more leaks.

As for the rear main seal...the short block went in to a reputable shop, and I supplied a Butler 1-piece RMS, which was properly installed this time.

The crank was polished, it was line honed, caps were repaired, new bearings and rings, and everything was weighed and balanced.

For the first time in 5 years, I am not leaking or burning oil, and the oil stays clean.

I have the 7qt milodon pan too, it uses the same older 3 prong U seal as the older late 60's pans vs the later 70's pans with 5 prongs. The later U seals are better than the older ones, from what Ive read the older U seals are notorious for leaking, the bead can roll if not installed exactly right & that causes leaks that look like a rear main leak.

wh33lman used the 1/4" cork gasket also with good results, I still say thats where your leak is from Rich.. providing the RMS was installed right the last time. I know pulling the engine is a huge hassle, I pulled mine 2 times after the initial install to fix the leak that was definitely the pan U seal.

I wouldnt want to selll a car just because of a leak, looks like with your Mom's help ;) you should be able to do a basic engine pull, leave the trans installed if you can for less work... then do the "tip test" before installing it again to be sure its leak free. Or pay a good shop to do it if you have the funds & dont want to mess with it yourself?

On these big cars, cant the pan be pulled with engine still installed? Its harder on your back but can be done.

Then I used my shop vac to push air into the oil fill hole on the rocker cover for 30 seconds. This slightly pressurized the crankcase.
When I removed the paper towel strips, they had oil on them, confirming it was the rear main seal leaking.
Turned out the con shop never read the instructions for the 2-piece vitron seal, and never sealed the anti-rotation holes with silicone prior to installing the seal.

Good tip, im gonna try this..................will also try to get a smoke machine..................the shop that did the work said they smoked it, by there work i think he meant he smoked one, but didnt inhale.

Scott, i think you might be right on that oil pan................this time i will use the cork piece i bought to put in the groove.

Another question i cant seem to get a answer from is "What if the shop didnt fill the anti-rotational holes" would that contribute to some leakage...........idk.

From what i read, its possible to change the oil pan gasket..................but most say way easier and to do a better job, pull the motor.

Once again appreciate all the help i get from you guys...............had the car out today, runs perfect, well except for the drip, drip.........lol

Rich

I bought the ME Wagner PCV valve and it helped with oil leaks a fair amount. I used a cheap manometer from Amazon, and confirmed that I was getting more negative crankcase pressure at idle and cruise with the ME Wagner than I was with a couple of different over-the-counter PCV valves. It's not cheap but it's worth a shot.

Still - those oil leaks you have are no big deal. Drive your car!

I’d kill to have a leak that small

I had a leak from the oil pan at the rear. It wouldn't leak cold. It would only leak when the oil was hot and thin. I've heard of using heavier weight oil, like straight 40 weight, running the oil a little low too. I installed a ME Wagner PCV which I think helped. I also considered adding a vacuum pump. Suck those drips back in. Just yesterday, I dropped in a 455 with the BOP one piece rear main and the one piece oil pan gasket with a new oil pan, the 64-69 style. Ultra black RTV in the corners and along the bend over the main cap. The pan doesn't have the alignment slots and has a raised bump along the curve for the main cap. The bump really pushes into the pan gasket hard. So far, drip free.

Maybe a long shot but did installer forget to put anaerobic sealer between rear main and block?

lol, thats a good question, he told me everything was done correctly, but then again he did a smoke test and no issues except for a slight leak at the front of the pan...............wouldnt surprise me if he didnt even fill the anti-rotation holes.

Im trying a few suggestions i got from my two posts about this, then figure out what my next move is.

Rich

In all my years and 5 engines in my 73 TA, it has always had oil leaks. Even using the latest greatist rear main seals, pan gaskets, valve cover gaskets etc. and permatex goup. Always had a fog of oil on the car chassis and small drip. Did some research on my breather PVC system and bought a Wagner dual adjustable PVC valve. Seems to have cured the problem. Poor mans evac system!

Great advice here. I've used anaerobic for years on rear mains in my Buick builds. I also use it between the 2 halves of the neoprene rear main seal that I use instead of the rope seal. I haven't had a rear main leak since I started doing it that way. Far superior to silicone.

If you did not install the seal yourself I wonder if it was installed not facing the right way.

Many seals are made such that they need some crankcase pressure to load the sealing lip onto the crank .