[Tokyo Torquer]

I have a real headache with a leaking rear main seal on me fresh engine. I beleive it is the seal, but have also been eyeing the back of the oil pan. You can see oil on the crank end, but cant tell if it is the main seal or the pan seal.

Here is what I have done in the last 1,000 since I first started the engine and notices the small but irritating leak, requiring me to pull the engine 3 times.
-changed oil pan gasket 3 times, used cork first time, 1-piece rubber the 2nd & 3rd time
-tried 2 different oil pans. The one on their now is an expensive Stef's fabricated aluminum job
-disassembled the engine, pulled the crank (brand new Eagle 4340 crank) and put in a second new rear main seal, taking care to off-set the seal parting line both times
-Check all other potential leak sources, using flourecent leak detection dye. I beleive it is the rear main.

I am totally stumped and aggravated after all this effort, it is still leaking all over the shiny clean bottom of my car.

The only remaining thing I can think of is the crank is machined wrong from the factory where the seal rides. I only use Fel-Pro seals. Any ideas??!!!

By the way, does anyone know if the Stef's pan uses a thick or thin front seal on the pan gasket? I am using a thick one as instructed by Stef's but the guy seemed very unsure of himself. I measured the gap and it seems like it needed a thick one, but the pan went on awefully tight in the front. This is not the leak issue mentioned above, though.

 

[SWHEATON]

Did you by any chance use stainless steel oil gallery plugs in the rear of the block that are located approx half way in between the top 7 bottom of the block?

I have seen these leak oil down the back of the block looking as though its the oil pan,pan gasket,or main bearing seal and can drive you nuts so check this out if you happen to pull the motor again but it's hard to see it with fresh clean oil. So if your going to pulll the motor again i would get an oil leak dye kit with blk light and run the die through the motor before you pull it. Then when the motor is out all you need to do is hit the back of the block to see if it lights up where the oil galley plugs are because this could be your problem.

My machinest made the mistake of putting all new stainless oil gallery plugs in my BBC and they all leaked no matter what you sealed them with.

I found out the hard way that stainless being a harder matrerial then the stock cast oil galley plugs doesn't crush well enough when tightened to seal properly even with sealer. I also read about people having problems getting stainless steel brake & fuel lines to seal properly due to this same problem.

I had to replace all the galley plugs with the original stock cast plugs i lukily kept which i just cleaned up on a wire wheel and installed them with indian head sealer and ALMOST all the leaks were gone.

Unfortunately for me i could not change the 2 large stanless oil galley plugs in the back of the block behind the flywheel which still leaked. To fix i would have to pull the trany/bell housing/clutch/flywheel or the the motor so i know just how you feel.

I now have what i call a controlled oil leak whuc is not horrible but it leaks like a drippy main leak even though it's not which i have confirmed. The leak drives me nuts which knowing myself will drive me to pulling the motor again someday just to fix it.

Good luck.

Scott

 

[jtm60]

I am curious for more input on this one too..my buddy's car (we think) has a rear main seal leak (396)..its pretty minor really..but he is all ready to pull the motor. I watched him install the rear main seal, and I KNOW he staggered the split, and I know the seal was facing the right way..He did not use any type of sealant on the rear main seal..just put it together and continued assembling..I am wondering if he should have put some kind of sealant on the RMS? Also, I am wondering if the leak wont stop on its own..he really hasnt driven the car much at all since installing/breaking in the motor..do they 'run in' at all, or if its once a leaker always a leaker?

 

[snowtrav]

The leak is probably coming from under the rear crank cap,you need to get some gm gasket maker ( small red tube) and apply to metal areas that don't have a gasket on the rear and front caps.This is made for this purpose.I hope this helps.Also its not a bad idea to get a non hardening gasket sealant for the gaskets. as for the seals, wiping some engine lube on the seal that comes in contact with the crank this will prevent the seal from getting brittle on first time startup by reducing friction. this will cause the seal to leak.

 

[snowtrav]

I am curious for more input on this one too..my buddy's car (we think) has a rear main seal leak (396)..its pretty minor really..but he is all ready to pull the motor. I watched him install the rear main seal, and I KNOW he staggered the split, and I know the seal was facing the right way..He did not use any type of sealant on the rear main seal..just put it together and continued assembling..I am wondering if he should have put some kind of sealant on the RMS? Also, I am wondering if the leak wont stop on its own..he really hasnt driven the car much at all since installing/breaking in the motor..do they 'run in' at all, or if its once a leaker always a leaker?

The gm gasket maker i mentioned in the last post should also be used on the split seal ends when putting the seal together.if the leak is coming from this area it probably won't stop on its own.

 

[Tokyo Torquer]

Scott,

I did check those galley plugs when I pulled the engine, and the whole back of the block in that recess where the plugs are was completely dry.. dry as a bone. I have a block plate behind the scattershield, sealing it off, so definitely would have found the leak in there if there were one.

Also, the second time I installed the rear main seal, I used a tab of the red anaerobic sealer that was recommended by someone. It did not help. we also put oil on the seal lip, so you can see we tried everything!

 

[CNC BLOCKS N/E]

We have seen the stock type seals leak and we have always used the seals from Universal molded parts P/N 20350 it called a Pro-Fit seal as it is a red viton rubber seal and seems to grip the crank better as we sold one to a customer last week that repalced two rear seals Felpro and still had a leak bought a Profit seal installed it a called a few days later and said the problem was cured. Phone 1-800-626-2967 ask for Greg.

 

[jtm60]

carl (CNC)..is that the p/n for smallblock or bbc? I want to tell my buddy to order one for his 396..I think his leaky one is a felpro.

 

[Tom Mobley]

the things will leak between the seal and the block. There's a bead on the back of the seal that is real easy to scrape off when installing the seal into the block or cap.

Also, the point is well taken about leaking between the cap and the block. The cap is chamfered at the corners that seat into the block. Also, I've seen leaks where the pressure feed passage goes through between the cap and the block. Were the caps surfaced as part of an align hone job?

all it takes is a super thin film of quality RTV on the parting surface behind the oil preesure feed hole and thin wipe down the corners of the cap recess of the block.

Check the old seals to see the backside bead still in place.

Another thing you can do is fill the engine oil while it's still on the hoist, set it down and tip it back until you think the oil level is covering the entire rear main area. block it up and wait. you can use a little talcum powder to make the leak easier to see. Obviously, you'll want to plug up any other holes where it might pour out.

 

[Motorhead62]

I have a couple of questions:

What type engine?

New or used crankshaft?

Is the rear main installed backwards in the block and cap?

If using an old crankshaft: Is there a groove worn in the crankshaft were the seal rides? For Small Blocks, FelPro makes and offset rear main seal. For big blocks, I don't know of a fix for this.

Good Luck

 

[CNC BLOCKS N/E]

carl (CNC)..is that the p/n for smallblock or bbc? I want to tell my buddy to order one for his 396..I think his leaky one is a felpro.

For the BB 23454 is the P/N SBC 20350 and they also offer offset seals if there is a groove in the crankshaft.

 

[GOSFAST]

Rear Main/Pan Oil Leaks

This info pertains mostly to ALL the aftermarket BB's. On the Dart's you have to pay extra attention to the 2 rear oil pan bolt holes in the block itself. We had a pair leak on the dyno just recently, more noticabley after the test was completed, while the oil was really warm. Same pans and same pan bolts. Seems the bolts (2 rear corner) are "bottoming" in the block before the pan's tight (depends on the brand of pan bolts). We just started running a 5/16 bottoming tap in these 2 holes during the pre-assembly stage. While they were bolted on the dyno we simply used 2 shorter bolts at the back for confirmation. The Bow-Ties (low-decks) have the same problem, but the holes aren't in the block, theyr'e in the aluminum adapter G.M. uses to determine the rear main seal configuration (late one piece or early 2 piece) and also have "blind" holes and has the same risk of a leak at the rear. I have no 1 piece seal blocks (Bow-Ties) in stock so I can't include them here. The MK-IV's and the MK-V's (standard blocks) have "through" holes, no problem there. Thanks, Gary in N.Y.
P.S. You will find that many of the aftermarket pan bolts for the BB's are simply too short (for those 2 rear holes) due to the heavier 1 pc. gaskets, the "thicker" pan rails on some pans, and the fact that you lose the height of the main cap register before the first thread, so when you put longer bolts in they tend bottom out. You eliminate this problem altogether by using pan studs, but these have other issues.

 

[Hi-po SS 454]

it is still leaking all over the shiny clean bottom of my car.

I have the same problem on 4 year rebuild and my friends 69 alky the same on 1 yr rebuild, rebuilt by same person..

 

[Tom Mobley]

an experienced guy who is paying attention (and gives a rip) can feel the bolt hitting bottom before compressing the gasket. It just stops instead of tightening up gradually as the gasket is compressed. Wouldn't be hard to try some shorter ones....

 

[malex]

Your problem is likely with the wrong rear main seal. You likely have 400 mains and a block that has been align honed. You need a Fel Pro #2909 rear seal instead of the standard Fel Pro #2900.

During the align hone the lip that holds the seal gets turned down approx. .200 for the arbor to fit. A 2900 seal no longer fits properly.

Drop the pan, the pump, the rear cap and roll in a new seal. Reassemble and leak cured. Happens to lots of guys..

 

[BillyGman]

Your problem is likely with the wrong rear main seal. You likely have 400 mains and a block that has been align honed. You need a Fel Pro #2909 rear seal instead of the standard Fel Pro #2900.

During the align hone the lip that holds the seal gets turned down approx. .200 for the arbor to fit. A 2900 seal no longer fits properly.

Drop the pan, the pump, the rear cap and roll in a new seal. Reassemble and leak cured. Happens to lots of guys..

old thread alert. You do realize that this thread is 8 years old, right?

 

[CNC BLOCKS N/E]

Your problem is likely with the wrong rear main seal. You likely have 400 mains and a block that has been align honed. You need a Fel Pro #2909 rear seal instead of the standard Fel Pro #2900.

During the align hone the lip that holds the seal gets turned down approx. .200 for the arbor to fit. A 2900 seal no longer fits properly.

Drop the pan, the pump, the rear cap and roll in a new seal. Reassemble and leak cured. Happens to lots of guys..

Since this thread was back in 2005 I am sure its been addressed by now.

 

[camaroman7d]

Pretty sure it is not a problem anymore since he has a different engine in the car now.