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Old 10-03-2011, 09:02 AM
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SBC Rear Main Seal.

Need a little guidance in Removing & Replacing a "Rear Main 2 piece Seal" on 400 SBChevy. Engine is in vehicle, Flywheel & Muncie attached to it. Any Special Tools required? Any previous experience or what to lookout for, etc would be greatly appreciated. Thanks .

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Old 10-03-2011, 01:27 PM
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Nope. Just drop the pain, drop the oil pump and rear main cap. you can push the old seal out then push the new one in. However, when you finish don`t be surprised if it still leaks.
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Old 10-03-2011, 03:54 PM
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Quote:
Originally Posted by afsog
Need a little guidance in Removing & Replacing a "Rear Main 2 piece Seal" on 400 SBChevy. Engine is in vehicle, Flywheel & Muncie attached to it. Any Special Tools required? Any previous experience or what to lookout for, etc would be greatly appreciated. Thanks .
Drain the oil overnight if possible so you don't make too much of a mess when you pull the pan off. You will probably need to raise the engine a few inches up off of the motor mounts to give you room to remove the oil pan. Use wooden blocks to rest the raised mounts on.

Once the bolts are out of the cap you can use them to wiggle the cap back and forth to get it out. It's OK to tap it lightly on one side then the other if you want to do it that way. Cleaning the cap is easy but the groove in the block has to be spotless, too. Hopefully the guy before you didn't smear the back of the seal w/RTV or something like that to "help" seal it. Carb spray and a length of copper wire can help w/this, but watch out for overspray and keep your eyes protected at all times w/safety glasses.

Be sure to smear the surfaces of the seal that rides on the crank w/motor oil and actually it won't hurt to lube up the whole top seal to help it slide into place. Seals usually to come w/a little piece of plastic used to protect the seal that goes into the block from getting scraped or damaged going in. Use it sort of like a shoe horn, if one isn't supplied you can make one from some thin, tough plastic like an old photograph negative.

There will be a lip- this faces the engine and the seal should come w/a diagram showing this. There are two schools of thought regarding the seal parting line- some say to offset the seal halves so the seal parting lines are not in line w/the cap parting line. Some say to use RTV on the ends of the seals- personally, I don't. But then I also don't replace the RMS w/the engine in the vehicle.


OFFSETTING SEAL ENDS

Use RTV on the spotless rear main cap on the areas in green shown below. You don't need too much, just a light coat:



While searching for a photo of where to put the RTV I ran across THIS page- seems to cover it pretty well. Youtube will no doubt have videos, too.

Note- Just in case you hear this somewhere, back in the day often the crank caps would all be loosened a couple turns to allow the crank to drop down some. This was mainly when rope seals were used. There's no need to do this w/the rubber 2-piece seals.
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Old 10-03-2011, 06:34 PM
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There is also an offset seal available incase your crank has a groove wore into it. It happens on high milage engines.
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Old 10-04-2011, 08:31 AM
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SBC Rear Main Seal

Thank you all for your input. Appreciate all the advice. Now here comes my next question: Oil Pan is removed, Looking from the floor up into Crank, Flywheel, rear section of engine, I do not notice any leaks especiallt where Crank meets Flywheel.?? It appears pretty dry . So, how exactly do I determine if Seal is Leaking or not? Just not sure guys. I quess I could put Oil Pan back on with New 1 Piece Gasket & hope for the best. Just don't know what "Rear Main Seal Leaking looks like. Thanks Again to all.
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Old 10-04-2011, 11:26 AM
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The "tell" is the presence of oil at the crankshaft/rear main seal junction. The oil will leak down from there and should have left a wet trace. If that is dry and there's only oil from the pan seal down, it's the rear pan seal.

If this has been leaking for any length of time there will be dirt embedded in the oil (grease in other words) where there has been a leak. If the back of the block adjacent to the RMS looks much cleaner than the back of the oil pan, that's another indication it's the pan seal not the RMS.
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Old 10-04-2011, 01:46 PM
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Let me add to the advice given.

A rear main seal will only leak while the engine is running. When oil pressure is high.

A oil pan leak will only show up after the vehicle is driven.

Also check your oil pressure sender, or connection, if it is in the rear of the block.

A leaking distributor mounting gasket can also appear to be a rear main seal leak at times.
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Old 10-04-2011, 04:05 PM
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SBC rear Main seal Lk??

Again, Thank you all for inputs. Believe me, I am putting all this info to use. I actually took some pics of what I am looking at, from the floor upwards to the Oil Pump, Crankshaft, Bearing Cups? Mostly trying to get good pic of where Flywheel meets up with Crankshaft area. I have enclosed 2 pics of what I am looking at. Hope pics came thru.
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Old 10-04-2011, 06:09 PM
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Photos are inconclusive to me. How did the leak first come to light? Was it from a puddle on the floor, or from a low dip stick and/or oil burning on the exhaust while you were driving around- but no puddle, for example?
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Old 10-04-2011, 06:30 PM
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Sbc Rms

Engine has approx 2,000 miles. Professionally rebuilt by Ed Hayes Racing Engines of Santee, Ca. Eng. was Dyno'd & Tune ready for installation when rebuilt. Due to illness, engine was not installed until approx 4 yrs later. Eng. sat on stand in corner of garage covered. Engine was given to me as a gift from my Best Friend that passed on due to cancer. His wish was I install engine in my 57, 210. Noticed 1st leakage, around the 1,000 mile mark, started as a quarter size oil spot overnight. After not driving car for a week, same lk would be approx. 5 inches in diameter. Eventually, I R&R Cork Pan seal,( thinking it might have dried out). Replaced with a Fel-Pro Rubber One- piece seal. Another 1,000 miles go by with no problem. Couple of weeks ago, I parked car overnight & noticed oil spot in a.m. . Again, as a small quarter size, then gradually increasing in size with car being stationary. lk gets no larger than 4 to 5 " then stops.
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Old 10-04-2011, 07:10 PM
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As was mentioned earlier by carsavvycook, this is pointing more towards a pan seal/gasket problem.

If it were another leak like the oil pressure sender port at the top center rear of the block just aft of the distributor, the oil would need to leak down from there- and the drip would likely be off center as opposed to right in the middle of the engine.

The first thing I would have checked is the tightness of the pan bolts. Now that the pan is off, this obviously isn't an option any longer (and you might have tightened them before, anyway), so I would say to replace the pan gaskets and button it back up.

If you use the 1-piece oil pan gasket (which I would recommend), the instructions say to use no sealer. But it seems that about half use RTV in the corners of the front and rear "seals" where they meet the front cover and block at the front, and at the rear in the same place where the rear seal of the pan meets the block. If you do a search for sealing 1 piece oil pan gaskets you'll get more info on this.
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Old 10-04-2011, 07:26 PM
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Sbc Rms

Cobalt 327, Thank you for taking an interest in my issue. Your expertise is greatly appreciated. Received my 1 Piece Milidon pan seal today. Appears to be of much better quality than Fel-pro. This one has "Ears /Tabs" where it rides on Front & Rear of Oil Pan as to prevent from slipping off. Has washers built in , so unable to "Overtorque". I am going ahead with Installation of Pan & hope for the best. There are worst things out there. Like my friend used to say prior to his passing. "Hey, cars are like Dogs, they mark their spots" & If you don't like leaks, don't look under car. Just keep cking Dipstick . Again, Thanks to all that contributed to this. Much appreciated. God Save Our Troops. Wounded Warriors.Com. Good Night, AFSOG.
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Old 10-04-2011, 07:49 PM
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Quote:
Originally Posted by afsog
Cobalt 327, Thank you for taking an interest in my issue. Your expertise is greatly appreciated. Received my 1 Piece Milidon pan seal today. Appears to be of much better quality than Fel-pro. This one has "Ears /Tabs" where it rides on Front & Rear of Oil Pan as to prevent from slipping off. Has washers built in , so unable to "Overtorque". I am going ahead with Installation of Pan & hope for the best. There are worst things out there. Like my friend used to say prior to his passing. "Hey, cars are like Dogs, they mark their spots" & If you don't like leaks, don't look under car. Just keep cking Dipstick . Again, Thanks to all that contributed to this. Much appreciated. God Save Our Troops. Wounded Warriors.Com. Good Night, AFSOG.
I only use Milidon pan gasket's on performance engines. They are the best your money can buy. Use a little dab of silicone in each corner of the gasket, front and rear. I like permatex ultra black for this. A dab of this around the dip stick tube is always a good idea also.
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Old 10-04-2011, 08:07 PM
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Thanks Carsavvycook. Will comply with Permatex Silicone on all 4 corners.
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Old 10-14-2011, 11:12 AM
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mos def sounds like a oil pan leak from rear. my advise, coming from experiance with oil pan seals is one piece are to be used with a oil pan that has flat rails. as opposed to oil pans that have little bumps on the rails. those bumps are for 4 piece seals. they purpose is to push the cork closer to the block. i used a one piece fel pro on my milodon pan and it leaked. my pan was not flat, it had those bumps. this info was told to me by milodon and fel pro. i also used just a dab of RTV on the 4 corners of the block only. i like the autozone/cherckers 4 piece seals. and only use RTV on the 4 corners. usually i put the seals on the block then meet the pan and put the bolts on using extension and wrench and tighten with ONE HAND only, lightly. then after a couple hours i start the car and look for leaks and tight little more as need. if you need a day of curing u used too much damm RTV!!. a couple things to watch out for on the 4 piece seals....once u start tighten those bolts and u see the rubber piece start slipping out YOUR SCREWED!!!! the cork and rubber joint elbow just moved out of place and the leaks will begin.DONT OVER USE THE RTV!!!!!!!! most rear leaks weather there one piece or 4 piece will leak cuz of too much RTV on the front and rear mains. RTV can cause the seals to move when tightening.
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