Just to confirm- if you are attempting to replace a neoprene seal by removing the pan only, you are not likely to be met with success, so rope seal only in that case?
No, I wouldn't say that, Dave. It seems there's been a misunderstanding about this seal so let me try again to do a better job. Please look at the image below. The green arrow points to the trapezoid-shaped channel where either seal (rope or neoprene) will go. The neoprene seal has been designed to fit neatly in that channel and push against the crank with a wiping lip...the tip of which faces inward toward the oil pan. The rope seal must be forced into the channel and then pushed down (preferably with a tool...could be an improvised tool) to get as much of that rope seal in the slot and get it flattened and as evenly distributed as possible. The red arrow points to the small amount of space between the crank sealing area and the engine block. Your rope seal is currently in that channel and when it was installed it was squashed down (hopefully) so that a bit of that rope seal will be pushed over into that bit of space also. The nature of the installation of this seal, the tight space in which to work and the inability to install it as GM instructed with the crankshaft in the vehicle make installing the rope seal with the engine in the vehicle very challenging. And these challenges are what make failure of that seal (when installed with the engine in the vehicle) so common. Back when this seal was made with asbestos there were some mechanics who could replace them and have them work correctly...but those were not "dime a dozen" guys. They were rare and that rope seal was entirely differently made. Now, let me make the rope seal picture a little more bleak...today's rope seals are some sort of blended rope (cotton/poly maybe or possibly a nylon/poly rope) impregnated heavily with graphite. I'm not certain there is a knife nor razor blade on the face of this troubled planet of ours that can cut that rope without leaving frayed threads. I've tried many times and the moment that rope is cut the threads start to come apart. No matter how carefully and correctly the "new" rope seal is installed I think the loose threads are where the problem will begin. In contrast to the neoprene seal, the rope seal is designed to fit as firmly as possible against the surface of the crank. So it naturally wants to turn when the crank rotates...and it will almost invariably do that. And to hark back to replacing the rope seal, it is important to understand lowering the crank a bit is mandatory. You might be able to remove the old seal. There are tools made which look like stiff pieces of wire wound into a screw on the end...the idea being you could screw the thing into the old seal and pull it out while rotating the crank in the direction you're pulling. I should tell you I have made that little procedure work all of one time in almost 60 years of fiddling with these. If you drop the crank a bit, you will remove the pressure on that seal and you'll make it much easier to remove. Most commonly a "Sneaky Pete" tool is used to grab the end of the rope seal you're able to dislodge and help pull it out...this tool works like a Chinese finger trap. Bottom line is even if you're patient and lucky enough to remove the old seal without lowering the crank a bit you won't be able to install a new one correctly without lowering it. If you want to grade my paper on that, please ask Jerry, Evan, Panic...any of those guys.
Okay, on to the neoprene seal. Depending on how yours was installed, you might be able to push it out using the small end of a chopstick to get it started without lowering the crank, but it will be mandatory to turn the crank in the direction you're removing it. Here's why...when that seal was installed, there should have been a thin layer of non-hardening gasket sealer applied to the part which will fit into the channel...both to keep oil from seeping around it and to keep it from wanting to rotate with the crank. And that seal can not be straightened out as it is removed. In the center of it is a half-circle shaped piece of hard spring steel. If you have dropped the crank a bit you can free this type of seal and rotate it out. Installing a new one is going to go much better if you lower the crank...because you will need that thin layer of gasket sealer on it and installing without lowering the crank will wipe that off. If you decide to lower the crank a bit, here is how I do that: remove your transmission or slide it back enough to release the input shaft from the pilot bushing, remove the oil pan and harmonic balancer (important because you need some room there for the front end to drop also and you don't want to wreck that seal nor distort the timing gear cover. Then remove the rear main bearing cap and loosen all other main bearing bolts. Some will remove all the rod nuts, remove piston rod caps, place rubber hose on each rod bolt and push the pistons up and out of the way. But you can lower the crank without doing this...it just makes it easier to move the crankshaft.
And another word about the crank sealing surface. The old rope seal was known to harbor oil, moisture, acids, all sorts of stuff and consequently over time the surface of your crank might become pitted. In some cases pitted badly. For either of these seals to work at their best the surface of the crank must be as smooth as possible. Even for the one-piece seal to work well and be long-lasting this must be the case.
I hope this is helpful. If you have any questions at all, please mention them.
