1975-Replace Rear Main Seal Question
Thread Starter
Cruising
Joined: Jul 2017
Posts: 12
Likes: 4
1975-Replace Rear Main Seal Question
Hi all,
I am in the midst of replacing the rear seal in my 75. It is an old timey 350 where the oil pan, oil pump, and rear main cap must be removed to get to the 2 piece seal. Since I am replacing the pan anyway all of this stuff has been removed to work on the seal. I found an old article on this procedure by Bill Schroeder. http://www.corvettehacks.com/article5.html. I actually talked to him; nice guy. He suggested this forum for my question as I am confused by something he writes in the Top Seal Install paragraph.
"Be sure the lip seal is positioned towards the front of the engine (I understand that)this seal CAN easily be installed backwards - all mating surfaces should be clean and free of oil(NOTICE THE DESIGN: oil pressure is exerted against the lip forcing it to seal) (I understand that too)This statement has confused me though:
"Use a 3/8 inch offset so the bearing cap parting line does not line up with the seal parting linesimply push seal up in clyinder case 3/8 inch - this offset will be on the bearing cap as well" (I am confused here from open quote to close quote.
And then he writes which I do understand:
"Roll the seal around crankshaft using the tool as a "shoehorn" (I understand this too)
Any clarification on this would be very helpful. Removing this top seal has stymied me so far (can't get it out) so I am not to the point of installing the new seal.
BTW, I am using a Fel Pro 2 piece seal.
Best regards,
Tony
I am in the midst of replacing the rear seal in my 75. It is an old timey 350 where the oil pan, oil pump, and rear main cap must be removed to get to the 2 piece seal. Since I am replacing the pan anyway all of this stuff has been removed to work on the seal. I found an old article on this procedure by Bill Schroeder. http://www.corvettehacks.com/article5.html. I actually talked to him; nice guy. He suggested this forum for my question as I am confused by something he writes in the Top Seal Install paragraph.
"Be sure the lip seal is positioned towards the front of the engine (I understand that)this seal CAN easily be installed backwards - all mating surfaces should be clean and free of oil(NOTICE THE DESIGN: oil pressure is exerted against the lip forcing it to seal) (I understand that too)This statement has confused me though:
"Use a 3/8 inch offset so the bearing cap parting line does not line up with the seal parting linesimply push seal up in clyinder case 3/8 inch - this offset will be on the bearing cap as well" (I am confused here from open quote to close quote.
And then he writes which I do understand:
"Roll the seal around crankshaft using the tool as a "shoehorn" (I understand this too)
Any clarification on this would be very helpful. Removing this top seal has stymied me so far (can't get it out) so I am not to the point of installing the new seal.
BTW, I am using a Fel Pro 2 piece seal.
Best regards,
Tony
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
When you roll the seal in, do not align the ends of the seal at the block/ cap line. One end of the upper part of the seal should be about 3/8" above the block, therefore the other end should extend about 3/8" below the block line. Match this in the cap with the lower 1/2 of the seal. Put a small dab of sealer on the mating ends of the seal and also on the cap adjacent to but outboard of the seal to eliminate seeping of oil between the cap and block. A very thin application of the sealer is enough. Do not let any of it get near the main bearing.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
Yup. 75 ^^^ is right. Its called "clocking". In other words, the ends of the seal should be at: 8 'o cclock & 2 'o clock. Or 10 & 4 respectfully.
Never 9 & 3.
The better Felpro seals will come with a little tool to help guide the lip of the seal around. Its really quite easy. A pair of needle-nose will grab the upper seal or find something small, non-marring & flexible to push it out.
Never 9 & 3.
The better Felpro seals will come with a little tool to help guide the lip of the seal around. Its really quite easy. A pair of needle-nose will grab the upper seal or find something small, non-marring & flexible to push it out.
Last edited by HeadsU.P.; Jan 16, 2020 at 08:27 PM.
Racer
Joined: Oct 2017
Posts: 312
Likes: 64
From: Henry county ohio
A suggestion for your difficulty in removing the upper seal half.
loosen a couple main caps, it will allow the crank to sag a little, making it easier to install the upper half. IveI done it, and it helps. Once the seal is in place, re-install and torque the caps to spec. Then finish the seal install.
As mentioned earlier, a very small amount of sealer on the mating ends of the seal and cap. I mean small.
Good luck.
Jeff
loosen a couple main caps, it will allow the crank to sag a little, making it easier to install the upper half. IveI done it, and it helps. Once the seal is in place, re-install and torque the caps to spec. Then finish the seal install.
As mentioned earlier, a very small amount of sealer on the mating ends of the seal and cap. I mean small.
Good luck.
Jeff
Burning Brakes
Joined: Nov 2017
Posts: 780
Likes: 112
From: Redneck Riviera, FL
i'm in the middle of doing this for the second time and have found that there are a lot of different opinions about how to do this. for example, in the hacking site you referenced the author says to not put any sealer on the ends of the seal but fel pro says you should. i've been told to use rtv on the cap/block mating surfaces by one tech and to use anaerobic sealer by another. here's another reference: this one recommends putting sealer on the back side of the seal, fel pro say not to. i'm sure i could find other examples. one other thing, make sure the journal surface the seal rides on is clean and perfectly smooth with no corrosion. lotsa luck.
http://forum.grumpysperformance.com/...synthetic#p585
http://forum.grumpysperformance.com/...synthetic#p585
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
If you employ p#4 jeffwebley's "SAG" tip (a good one), you Can also roll old bearings out & new ones in: This is where PlastiGage IS recommended.
Roll out & inspect ... depending on crank journals' wear, often a STD set or a set that's only 0.001" more brings it right back within OE tolerances.
bearings typically available STD, 0.001", (some) 0.002", 0.010", 0.011", 0.020", 0.030" ... rods too.
you can "split" sets too: e.g. a STD half- shell + 0.001" half-shell = 0.0005"
If you split ... Mains get their thicker half-shell in the Cap while Rods get their thicker half-shell in the Rod itself.
https://www.musclecardiy.com/perform...earings-guide/
Roll out & inspect ... depending on crank journals' wear, often a STD set or a set that's only 0.001" more brings it right back within OE tolerances.
bearings typically available STD, 0.001", (some) 0.002", 0.010", 0.011", 0.020", 0.030" ... rods too.
you can "split" sets too: e.g. a STD half- shell + 0.001" half-shell = 0.0005"
If you split ... Mains get their thicker half-shell in the Cap while Rods get their thicker half-shell in the Rod itself.
https://www.musclecardiy.com/perform...earings-guide/
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
I have a small brass rod with one end tapered like a screwdriver. I put that on the end of the seal where the metal of the seal is exposed and tap gently with a small hammer, Never had a problem getting the old upper half of the seal out, and using brass, which is soft, means no chance of scratching the crank, Aluminum would work too. Once you get enough of the other end of the seal out so you can grab it with pliers, roll it on out.
And then wash the upper side of the block with brake clean to flush out any trash that my be up in there. I always buff the cap with a wire wheel to get any old sealer off. I use anerobic sealer on the mating surfaces- there is a picture in the service manual that shows exactly where to put the sealer.
I'll not get into the discussion of "clocking" the seal so the ends are not in line with the mating surface of the cap.
And then wash the upper side of the block with brake clean to flush out any trash that my be up in there. I always buff the cap with a wire wheel to get any old sealer off. I use anerobic sealer on the mating surfaces- there is a picture in the service manual that shows exactly where to put the sealer.
I'll not get into the discussion of "clocking" the seal so the ends are not in line with the mating surface of the cap.
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Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
https://www.oreillyauto.com/detail/b.../51531/4610186
I use this a LOT on rubber valve cover gaskets and other things.
It used to be blue and was called "hylomar"......the name Rolls Royce gave it.......
Jebby
I use this a LOT on rubber valve cover gaskets and other things.
It used to be blue and was called "hylomar"......the name Rolls Royce gave it.......
Jebby
Le Mans Master
Joined: Aug 2005
Posts: 6,541
Likes: 1,975
From: Temple Terrace Florida
Instead of using a aluminum or brass tool to remove the old seal, I used a wooden dowel. I used a box cutter to put a point on the dowel. If it slips, you will not gouge the crank. Jerry
Intermediate
Joined: Feb 2010
Posts: 38
Likes: 13
From: Twin Cities MN
https://www.corvetteforum.com/forums...-solution.html
tg11350 - I too struggled with how to get the rear main seal out of the block. See the above link for my solution.....I worked at it for a couple of afternoons before trying this solution. I offset the seals a small amount and put a very little smear of permatex ultra black on the mating surfaces.
Good luck - Don
tg11350 - I too struggled with how to get the rear main seal out of the block. See the above link for my solution.....I worked at it for a couple of afternoons before trying this solution. I offset the seals a small amount and put a very little smear of permatex ultra black on the mating surfaces.
Good luck - Don
Le Mans Master
Joined: Feb 1999
Posts: 8,351
Likes: 75
From: Tampa Bay FL
Are you certain it is the rear main seal leaking? I ask as I had a leak at rear main seal and fixed with a one-piece FelPro pan gasket (blue rubber) and a better, stiffer, NEW oil pain (MIlodon). While at it, I replaced the oil pump (Mellings, stock replacement) and the front timing cover with a stiffer unit (Canton).
I've not had oil on the pan from the mains since. Also, it helps to ensure that your leak is not from aging valve cover, intake or the distributor shaft seals; all can make it look like a rear main when they are oozing. Don't ask how I know
I've not had oil on the pan from the mains since. Also, it helps to ensure that your leak is not from aging valve cover, intake or the distributor shaft seals; all can make it look like a rear main when they are oozing. Don't ask how I know
Melting Slicks
Joined: Oct 2000
Posts: 2,144
Likes: 195
From: Englewood FL
I have had better success in getting a leak free job by not offsetting the seals. When I tried offsetting them I had trouble measuring them so the offsets were the same on both the upper and lower halves. In addition, when installing the bearing cap, I was concerned it is very easy to slice the ends of the seals, since both halves are protruding outward on one side.
Felpro makes at least three different part numbers for rear main seals. I had the best luck with the offset part numbers, which position the seals in a slightly different position on the crankshaft.
I also purchased a brass punch set, and use one to tap against the upper seal to move it , so the other end can be grabbed with a long nose pliers.
Felpro makes at least three different part numbers for rear main seals. I had the best luck with the offset part numbers, which position the seals in a slightly different position on the crankshaft.
I also purchased a brass punch set, and use one to tap against the upper seal to move it , so the other end can be grabbed with a long nose pliers.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
i have had better success in getting a leak free job by not offsetting the seals. When i tried offsetting them i had trouble measuring them so the offsets were the same on both the upper and lower halves. In addition, when installing the bearing cap, i was concerned it is very easy to slice the ends of the seals, since both halves are protruding outward on one side.
Felpro makes at least three different part numbers for rear main seals. I had the best luck with the offset part numbers, which position the seals in a slightly different position on the crankshaft.
I also purchased a brass punch set, and use one to tap against the upper seal to move it , so the other end can be grabbed with a long nose pliers.
Felpro makes at least three different part numbers for rear main seals. I had the best luck with the offset part numbers, which position the seals in a slightly different position on the crankshaft.
I also purchased a brass punch set, and use one to tap against the upper seal to move it , so the other end can be grabbed with a long nose pliers.
Melting Slicks
Joined: Jul 2006
Posts: 2,291
Likes: 493
From: Salmon Arm, BC
My opinion is to buy the better seal, and install it the way the General Intended it to be installed. A bit of lacquer thinner to clean the surfaces the seal goes into and to clean the ends of the seal before putting a very small amount of sealant on. also clean the register that the main cap sits in and put a minute amount of sealant along the last inch of the register.
Done this way you won't have leaks.
Premium Viton seal
https://www.summitracing.com/parts/f...make/chevrolet
Done this way you won't have leaks.
Premium Viton seal
https://www.summitracing.com/parts/f...make/chevrolet
Thread Starter
Cruising
Joined: Jul 2017
Posts: 12
Likes: 4
i am the one who originally posted this issue on 12/18. It is now the 26th. I appreciate all of your helpful posts. My son came over today and we were able to get the top seal out...finally. Actually he did it. Obviously I'm relieved. We used the brass punch method with a socket extension taped to the end to make it longer. Then used your posts plus Fel Pro Tech Support plus reputable Youtube vids to install the new two piece seal, oil pump and end cap. BTW, I have a 2 post lift in my garage. Best tool I ever bought. I couldn't imagine crawling under the car as many times as I would have using a creeper.
Thanks again.
Thanks again.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
I disagree with clocking the seal. They didn't use exhaust manifold gaskets because the 2 machined surfaces sealed just fine. I betcha the main saddle to block machines surfaces do too. You try to feed 3/8ths of a seal up into a blind hole while installing a main cap bad things can happen. I have never seen a 2 piece main seal installed offset in any engine I tore down.
Last edited by derekderek; Jan 27, 2020 at 06:54 AM.
1st Gear
Joined: Mar 2020
Posts: 1
Likes: 0
Hi all,
I am in the midst of replacing the rear seal in my 75. It is an old timey 350 where the oil pan, oil pump, and rear main cap must be removed to get to the 2 piece seal. Since I am replacing the pan anyway all of this stuff has been removed to work on the seal. I found an old article on this procedure by Bill Schroeder. http://www.corvettehacks.com/article5.html. I actually talked to him; nice guy. He suggested this forum for my question as I am confused by something he writes in the Top Seal Install paragraph.
"Be sure the lip seal is positioned towards the front of the engine (I understand that)this seal CAN easily be installed backwards - all mating surfaces should be clean and free of oil(NOTICE THE DESIGN: oil pressure is exerted against the lip forcing it to seal) (I understand that too)This statement has confused me though:
"Use a 3/8 inch offset so the bearing cap parting line does not line up with the seal parting linesimply push seal up in clyinder case 3/8 inch - this offset will be on the bearing cap as well" (I am confused here from open quote to close quote.
And then he writes which I do understand:
"Roll the seal around crankshaft using the tool as a "shoehorn" (I understand this too)
Any clarification on this would be very helpful. Removing this top seal has stymied me so far (can't get it out) so I am not to the point of installing the new seal.
BTW, I am using a Fel Pro 2 piece seal.
Best regards,
Tony
I am in the midst of replacing the rear seal in my 75. It is an old timey 350 where the oil pan, oil pump, and rear main cap must be removed to get to the 2 piece seal. Since I am replacing the pan anyway all of this stuff has been removed to work on the seal. I found an old article on this procedure by Bill Schroeder. http://www.corvettehacks.com/article5.html. I actually talked to him; nice guy. He suggested this forum for my question as I am confused by something he writes in the Top Seal Install paragraph.
"Be sure the lip seal is positioned towards the front of the engine (I understand that)this seal CAN easily be installed backwards - all mating surfaces should be clean and free of oil(NOTICE THE DESIGN: oil pressure is exerted against the lip forcing it to seal) (I understand that too)This statement has confused me though:
"Use a 3/8 inch offset so the bearing cap parting line does not line up with the seal parting linesimply push seal up in clyinder case 3/8 inch - this offset will be on the bearing cap as well" (I am confused here from open quote to close quote.
And then he writes which I do understand:
"Roll the seal around crankshaft using the tool as a "shoehorn" (I understand this too)
Any clarification on this would be very helpful. Removing this top seal has stymied me so far (can't get it out) so I am not to the point of installing the new seal.
BTW, I am using a Fel Pro 2 piece seal.
Best regards,
Tony
When you roll the seal in, do not align the ends of the seal at the block/ cap line. One end of the upper part of the seal should be about 3/8" above the block, therefore the other end should extend about 3/8" below the block line. Match this in the cap with the lower 1/2 of the seal. Put a small dab of sealer on the mating ends of the seal and also on the cap adjacent to but outboard of the seal to eliminate seeping of oil between the cap and block. A very thin application of the sealer is enough. Do not let any of it get near the main bearing.