Preventing SBC Rear Main Oil Leak - What is the Trick???

Thanks, Dave. I' ll take a look at Summit and Felpro.

 

I don't recall having one leak. Had a customer bring one back for a seal leak but he had knocked the cam plug loose changing the camshaft. I had a newer pickup with the one piece seal leak at 200K. I use 3M adhesive to glue the gasket to the pan. There shouldn't be any pressure on the seal. There is a space between the bearing and seal. It has to be a crankcase pressure issue but I've seen motors blow oil out the valve covers that didn't leak out the rear main.

 

Dave-
I found the one piece oil pan gasket on the Felpro site:

OS 34509 T for the thin front seal
OS 34510 T for the thick front seal
They come with bolts/studs. List is $31.95 at Summit, $29.99 at Autozone.

 

What I was told by a engine builder was to use black weather strip adhehsive on the oil pan gasket and front and rear seal. Put plenty in the seams of the gasket and seals. He also said it would be a pain to clean off it you had to remove it. I had tried other suggestion without any success so I tried this and its been on there a year now with no drips or leaks at all.

 

An often overlooked problem can be the intake end seals leaking,...oil runs down the rear of the block, and comes out right where a rear seal leak would show. We found that happening on a few customer cars.

4TTRUK

 

agreed: Check

Oil sending unit
Intake man gasket
Valve cover gasket

all can drip down and fool ya.

 

Felpro makes 3 seals you can use! The standard seal, the offset seal, and a double lip seal. Chose the one that fits your needs!

 

While contemplating my options after reading all the posts, I figure I'll go for a one piece gasket eventually but for now I went over all the oil pan bolts with a socket and nipped them up a little.
It seems to have reduced my leak by more than half for now which pleases me.

 

Put a Ford engine in it!

 

Actually, I must confess to being mostly a Ford engine guy and this is the 1st SBC engine in a running project vehicle I've had.

However, it was not really thru choice as can be understood in my build thread:
http://www.jalopyjournal.com/forum/showthread.php?t=366906

 

sorry to revive an old thread but in searching this is the only mention of this i
could find. i'm trying to replace the rear main seal on '68 327/300 sbc. when i
looked at the rear main cap i noticed there was a small dowel pin driven in
between it and the pan rail. post number #18 by ground pounder mentions that it's
for setting rear main bearing thrust. with this in mind what's the procedure for
r and r'ing the cap? thanks.

 

I don't think that it's used for "setting" the thrust...it's used instead to align the cap, so the thrust bearing surfaces on the cap and block are in the same plane.

I don't worry about it, I just take the cap off, clean everything well, install a new seal (with the ends slightly offset from the parting line of the cap and block), and put some sealer on the parting line between the seal and the pan gasket end seal area. And bolt it back on.

 

If the mains are loose. and you have excessive blow by a new seal aint gonna fix anything. Ive seen those electric oil sender units leak and folks thought the rear main seal was bad. also the gasket at the rear of the intake and the valve covers can leak and look like a bad rear seal.

 

jim, just leave the pin where it is and it'll stay put when i pull the cap?

old wolf, i think i've chased down just about everything but the rear seal.
everything above and at the rear of the intake now looks good. i've been
putting it off but it leaks worse than the Deepwater Horizon and i can't
avoid it any longer.
thanks guys.

 

Yes, the pin should be pressed into the block, leave it alone.

 

jim, as always, your advice is much appreciated.
thank you sir.

 

well i installed the new felpro BS118291 double lip (the journal had a very slight wear groove) rear main seal but no joy, it still leaks. i have the tranny out as part of a power glide to th350 swap so i'm going to have another go at it. when i examined the seal it looked like new; no nicks or chunks missing and the molded ridge between the back of the seal and the block/cap had not been shaved off when i installed it. i tried to be very careful and meticulous on the last install so i really don't know what i can do differently this time. there's a lot of conflicting info out there, even differences of opinion between fel pro techs. about the only thing i didn't do was use a sealer between the back side of the seal and the block/cap. some folks seem to think this is a good idea even though fel pro says to install then dry. i've got a new fel pro 2912 to try this time. supposedly it's the same one that GM supplies as a replacement. i'm hoping some one here can give me a little insight. (jim?) thanks.

 

Change it to Ford Power ! No ! Really they are tough not to get a drop or two from any early Chebbie . They switched to one piece rear main seal for a reason . That was big money to redesign and tool up for the change . It was done for a reason .

 

Do you have a PCV? strangely Ive never had a rear seal that leaked on a small block chevy. I always run a PCV. Ive had front seals that leaked and once it was due to a chrome timing cover that wansnt centering the seal with the crank. Several times I found a groove worn in the balancer. a wear ring fixed the worn balancer

 

How bout this Ford cure............rotate the seal so the parting line is down in the block.
THEN......take your pan gasket to your garage door and slang it just as far as you can into the woods!!
Clean the 'flat surface' of the pan VERY well with lacquer thinner(NOT paint thinner!)....Clean the mating surface of the block VERY well with the same....LACQUER thinner! Buy a tube of Ford blue RTV and squirt a nice, thick continuous, line of RTV all along the bottom of the engine and along the bottom of the front cover. Set the pan (not be scoot'in it around) straight down on the bottom of the engine and torque the bolts in sequence. Leave it alone for 24 hours until everything sets up.
Welcome to your leak proof oil pan!!!
Say a short prayer that you don't need to remove the pan anytime in the near future because.........that-dude-is-stuck!. Putty knife and hammer to remove stuck.
6sally6

 

You can buy one piece silicone pan gaskets for Chevys, they usually work well if you have an original old oil pan.

Did you offset the new seal, and use aviation gasket sealer between the cap and block, between the seal and the pan gasket?

How are you making sure the oil is not coming from above, or below, or next to, the crank seal?

 

thanks for the input guys. guess i should start with this is a late 327 with a '68 casting date with sealed valve covers, rear breather tube, and pcv plumbed into the oil filler tube at the front of the block. it has a strong vacuum signal through the pcv valve and the filler cap looks like it seals well. the valve covers were leaking but are now dry. there are no leaks at the intake/chinese wall or the plug under the edge of the intake there. the oil sender and the distributor base are also dry. the welch plugs at the back of the block are also dry. the back of the flex plate is dry. in addition to the leak at the seal there is a lot of oil finding it's way into the starter but it doesn't look like the flex plate is flinging it there. and we're not talking a little seepage. i'm not the first one to try and fix this. it looks like the po or his mechanic had also tried. there was a new felpro one piece oil pan gasket and rear main seal with lots of rtv slathered everywhere.
when i did the seal i offset/clocked the ends about 3/8" with a dab of rtv on the ends and on the mating surface between the cap and block as fel pro recommends. i also polished the journal where the seal lip rides and cleaned all surfaces thoroughly with laquer thinner. thanks again.

 

Sounds like you're doing the best that can be done....hmmmm....

 

he just said he has one....

 

Early style valve covers on a late 68 large journal block, could the rear breather tube be blocked ?
Could be building crankcase pressure.
Pictures Please

 

tickety boo, good point, i haven't had the intake off and don't know the condition of the tomato can or if it even has one. but i can blow through it.
i should also mention that the i did mic the journal and it was +or- .001" of 2.40". apparently, that is on the low side of the spec but would think the seal should be able to handle that. i also checked the journal for run out and i didn't see any. also, the engine starts, runs, and idles well with no smoke out the exhaust. however, it does appear original and unmolested so original bearings, rings, valves and valve seals, etc.
jim, do you prefer permatex to rtv? and how do you feel about putting some kind of sealer between the back of the seal and the block and cap? when i pulled the new seal i had installed it looked like oil was getting between it and the cap. of course that could have been my fault and not the seal.
thanks.

 

I know you said the rear of the block is clean, no welch plugs leaking, and I'm guessing, the same applies to the cam journal soft plug? Years ago, I bought a 58 Chevrolet P/U truck that someone had installed a 55, 4 barrel, 265 in. And, it had a "rear main seal leak". I replaced the rear main seal and pan gasket; course it had the old style rope seal, and that was fun getting the top part of the seal in place (engine still in truck and me lying in the street in front of our house). After replacing, it still leaked, so, I replaced it again, and it still leaked!. I did everything right, everything was clean, everything was done with quality parts. I planned on doing it a third time, but also addressing the clutch assembly this time as it was getting oil soaked from the rear main seal leak. When I pulled the flywheel, I saw the problem. The camshaft plug was COCKED in it's bore, and that was the leak! When I went in to get a new plug, I got an education. Someone had used a "thick" plug, and with 265's, you have to use a "thin" plug. Whenever that engine had been assembled, and the soft plugs installed, once the camshaft was inserted, it contacted the thick plug and cocked it in it's bore, and it went un-noticed, until I found it. So, you Chevrolet guys, be sure and check that rear plug when assembling a 265, and use a thin plug. I am Butch/56sedandelivery.

 

If you have a good PCV at the filler tube with a good vacuum source, try blocking off the breather tube. This will prevent pulling air through it instead of the crank case.

 

^^56sedandelivery^^

I wonder if this is what happened to my 58 original 283 with rope seal? I rebuilt it, and on installation, leaked heavily on startup. Replaced, leaked. Replaced clocked, leaked. Replaced clocked and staked, leaked. New reground crank, still leaked. Had pcv system. Finally bought a '79 350 from neighbor kid, rebuilt it and all is fine many years later.

 

I use RTV in places like the end of the intake manifold to block, and the corners of the oil pan gasket...but that's about it. I use brush on gasket sealer for the rest. I don't see any reason to add sealer to the back of the seal, but if the lip it fits over is nicked, that might be where a leak is coming from. I don't know how carefully you looked at everything...I suspect you've been giving thorough looking at, for issues like this?

There was that Mopar that I put the lower half of the seal in backwards...but we won't talk about that....