[67blackcherry]

Greetings - the rear main on my '68 GTO is leaking....questions....

1) I have to remove the crank to replace the rear main seal, correct?
2) If so, the engine needs to come out, correct?
3) Leave the engine in and do this repair with the car on a lift?
4) Can I just remove the crank but leave the rods / pistons etc. in place? (Yes, I know I have to take off the bottom caps of the rods....I'm not that stupid...)

I'm reluctant to do this because the engine runs so strong (if it ain't broke don't fix it) and if I have to tear down the engine, I may as well get a stroker kit which just is not in my budget right now.

Thanks.

[Nicks67GTO]

Originally Posted by 67blackcherry

Greetings - the rear main on my '68 GTO is leaking....questions....

1) I have to remove the crank to replace the rear main seal, correct?
2) If so, the engine needs to come out, correct?
3) Leave the engine in and do this repair with the car on a lift?
4) Can I just remove the crank but leave the rods / pistons etc. in place? (Yes, I know I have to take off the bottom caps of the rods....I'm not that stupid...)

I'm reluctant to do this because the engine runs so strong (if it ain't broke don't fix it) and if I have to tear down the engine, I may as well get a stroker kit which just is not in my budget right now.

Thanks.

1-No
2-No
3-Yes but its going to be a pain in the ass
4-Dont need to do any of that

Call Wade @ BOP. He set me up with a Viton seal and some instructions on how to do it with the crank in the engine. All you have to do is pull the back cap and follow instructions. Mine is bone dry after the install. I'm very happy with the product and Wade is a top notch cat to deal with.

[David Jones]

Is it possible that you could relieve some crankcase pressure and stem the tide a bit? My engine leaked everywhere when I got the car. Over the years I've corrected the function of the PCV system, added a breather line off of the passenger side valve cover to the air cleaner base and found that "high mileage" 10w-40 oil really does have some benificial properties. Now mine only leaks slightly.....which I think is fairly "normal" for a old Pontiac that might sit around from time to time.

[David Jones]

I'm soon to fix my leak with a 455.......

[rohrt]

First you should make sure its the rear main that is leaking. There have been a few cases on this board where the rear gasket had pushed out on the pan. This happened to me.

next question is what rear main will you use? Rope or Viton.

[67blackcherry]

^^^ Viton - I used those in my LeMans (455) and Firebird (400) and they never leaked.

[hurryinhoosier62]

Paul,

That's probably the best way to go. Installing a rope seal UNDER the car IS NOT an easy project.

[A.J.]

Ok, let me in on the secret. Is the viton seal possible to install with the engine in while the standard rope seal isn't? Or is the way to go pulling the engine out in any case?
Looking at a possible bad rear seal on the 389 so I'm very interested in this subject.

[intense]

I pulled my engine twice put 2 different viton seals in and both leaked ... Then heard that if your crank has those cross hatch marks on it that it will leak .. pulled it the third time put in a rope seal .. no problems! I used the Graphtite seal from Best gasket company .

[Half-Inch Stud]

My 68 GTO rear mian also leaks. I think it's the car...

Seems cheaper & more assured to install a vacuum pump. No blow by, so probability of success is pretty good. You could consider keeping the oil pan on huh. HIS

[David Jones]

I think I'd try checking for a small problem before I pulled a motor.

[lust4speed]

I think BOP's advise on an in-car replacement with their seal is only recommended on the 3" mains. The 3-1/4" mains have to have the anti-rotation holes filled with silicone which is pretty near impossible with the crank blocking access to the holes on the 421, 428, 455 blocks.

I've done two rope seal replacements for friends lately. Both 455's. Engine upside down on the engine stand with the pan and timing cover, timing chain, main caps, and rod caps removed. Push the pistons down until they touch the head. Crank will lift right out if your back is up to it. Then you have all the room you need to do the job correctly.

Putting the crank back in is a little more tricky. No matter how the crank is positioned, two of the rod journals will hit the ends of the rods. It helps to have an additional set of hands, but one person can do it. The offending rods must be held in position aligned with the two rod journals while the crank is lowered into position. Install these caps first, then eyeball the rods and pick which ones have to install next. I seem to always have to lift the crank about 3/8" to swing one of the rods into position so it can be installed. The remainder of the rods will pull right up to the rod journals.

I use Ultra Gray to seal up the tips of the rear main cap and on the rear of the pan. Seems like we've had an epidemic of leaks dripping out the alignment holes on the rear, or maybe I'm getting all the fix-it calls. Seems like it is about 50/50 on whether the seal is leaking or the gasket around the rear main is leaking. Whether you have the early style cap with the groove or the flat late style, waiting at least overnight for the sealant to set up is the way to avoid the gasket leaking. I think that most of the pan gasket failures are caused by adding oil before things set up. This allows the oil to get under the sealant and breaks the bond. Once it is dry (I'm now waiting a full 24 hours), it creates a super bond with the metal. This area is just about the only place on the engine I use silicone, and I use enough so some is squished out and forms an additional boundary between the seal and oil.

Here's one of the engines ready for the crank to go back in. You have to look to see the rods after they have being pushed down out of the way.

[Nicks67GTO]

Not true. I did it on a 3.25" main and followed the instructions. It has worked just fine. Yes you have to fill the holes with silicone. Its all in the instructions. You need red high temp silicone and laquer thinner. Push the silicone through the block side with the viton seal a couple times to fill the holes, clean the seal up clean the crank up and cut the seal to length and put it together. It rakes 20 minutes once everything is ready.

[lust4speed]

It only takes me 5 minutes to install a rope seal "once everything is ready". Of course everything won't be ready for me until the crank is out.

[rohrt]

BOP explained to me that much of the success of zero leaks has a lot to do with the casting of the groove for the seal. If their is a core shift a rope seal is the better choice. If the groove is uniform then they recommend the viton seal.

[old66tiger]

I know that when SD Performance puts their engines together, Dave only sets the seal crush to 0.010" to avoid distortion of the seal when assembled.