are you packing the seal tightly into the groove? I havent had any success with those seals without fully removing the crank.

Tony

@anthony-williamson Yes the crank is out and pressing and rolling the seal in per shop manual but when I torque down all the mains the crank binds if I leave the rear main fairly loose I can turn the crank so it is definitely the seal that is causing the problem.I detest that seal,my Dad's 54 sedan that he bought new always left oil in the driveway he had sand on that spot for years. Frank.

Hi Frank, Tony and anyone else that has trouble putting in a rope rear main seal, join the club especially when trying to put a rope seal in the groove with the crankshaft in place. There are many seasoned mechanics who had to apologize to the man upstairs after doing one of these jobs.

A Best Graphtite rope rear main seal and even a rubber rear main seal relies on a whole lot of variables to make the installation a success.  As a Best Gasket dealer of the rope and rubber rear main seals for a variety of vehicles, I get a lot of questions on this topic. The main variables between using a rope seal or a rubber rear seal depends upon the seal groove depth and width, machining surface of the seal groove and the centering of the seal groove to the centerline of the crankshaft. 

A Graphtite rear main seal has to be installed in the seal groove dry as these seal ropes are a Teflon braided rope impregnated with graphite under press and are very slippery. Before the rope seal is fitted or "rolled" into the crankshaft seal journal diameter, some engine oil it put on the seal to prelube it. Once rolled to the correct size the end of the ropes are cut off to about 1/32 inch so the seal end will clamp together to make a good seal when they come together. The same thing is done to both grooves except when installing the upper rope in chassis. The rope that is longer is completely rolled to the journal size using the main cap seal groove as a jig. This rope can be lightly oiled all around to ease installation. Rope seals were used for years because they are self fitting and will fit into any machining irregularities. 

A rubber rear main seal is much easier to install but the drawback is seal journal condition because of the small sealing area of the seal lip and the groove depth, groove width and groove centering to the crank journal is very specific at plus or minus .020 inch. Seal groove to deep and the seal will not clamp together. To shallow groove and the seal will deform. 

I can't attach the file of information I have that goes out with every rear main seal so here they are. 

Pros and cons of rope verses rubber rear main seal

The pros about a rope seal is that it will conform better to the groove in the block and rear main cap that is not accurately machined, left as rough casting and/or off center with the center line of the crankshaft as the rope seal is hand molded or rolled into the groove to the approximation of the size of the crankshaft seal journal. The crankshaft, once installed, sets the ID of the rope seal to mate with the crankshaft. The sealing width of a rope seal on the crankshaft seal journal is around 3/16-1/4 inch wide once installed. This is a lot wider compared to a rubber seal which seals in a very thin area. If done correctly, these will last for a long time and not leak.

The cons about a rope rear main seal is the work it takes to install one. If the rope is not set or rolled in properly, it will of course leak.  A rope seal that is rolled in too flat will not make enough contact with the crankshaft seal journal causing a leak were as a rope seal that is not rolled in enough and fitted to tight to the crankshaft seal journal will cause enough friction to melt the rope seal causing a leak or spin the rope seal in the groove if the groove is smooth enough.  

The pros about using a rubber rear main seal is the ease of installation if a rubber rear main seal can be used.

The cons about using a rubber rear main seal is the machining accuracy of the groove in the engine block and rear main bearing cap concerning the width of the groove, the depth or OD of the groove, the centering of the groove compared to the center line of the crankshaft and the surface machining quality. The accuracy needed to use a rubber rear main seal is in thousands of an inch. A rubber seal can sometimes be shimmed up if the groove depth is too deep. When the seal groove is rough cast, the seal can leak on the back side as it will sit on the high spots of the rough casting. The centering of the groove compared to the centering of the crank will also affect rubber seal performance. The seal may fit tight on one side but too loose on the other side. If the crankshaft seal journal has been ground down smaller than original size at some point, this will affect the tension on a rubber seal and the seal may not actually touch the seal journal.

The machining of the main bearings compared to the crankshaft seal journal can really affect performance with both a rope and rubber rear main seal. If the main bearing journals are ground off center from the centerline of the crankshaft (not set in the crankshaft grinder properly), this will make the seal journal if not ground become an eccentric with a high spot and low spot. The high spot will form a rope seal causing it to leak at the low spot. The same will happen with a rubber seal as it will not have enough contact in one area.

NOTE: Both rubber (especially) and rope rear main seal oil leakage can be caused by a compromised PCV (positive crankcases ventilation) system. This will cause a build up of excessive crankcase pressure in the engine and will result in engine oil leaks not only at the rear main seal area but other areas of the engine as well. This can be caused by a stuck PCV valve, an incorrect oil fill cap as some are vented, a partially blocked or plugged road draft tube or a improperly plumbed PCV system. 

Replacing the engine rope or rubber rear main seal in chassis

Block rear wheels of vehicle. Jack up vehicle if needed and place on jack stands or comparable to access underneath of vehicle. Loosen motor mounts, jack up and support engine if needed to remove oil pan. Drain oil and remove engine oil pan. Remove rear main bearing cap. Loosen all main bearing cap bolts until they are just loose being careful to not loosen the front main bearing bolts too far. On engines with shims between the main bearing cap and block, be careful not to damage these as this will affect bearing clearance. If the front of the crankshaft drops too far it can damage the front crankshaft seal. Do not remove them all the way. Tighten the bolts back up hand tight. This allows the rear of the crankshaft to drop slightly aiding removal and installation of the new seal. Remove the old upper rear main bearing rope seal. Do this by using a wooden dowel or comparable tool to push on one side while pulling on the other side. Be very careful not to hit, gouge or scratch main bearing journal seal surface. Use small wire or comparable tool to make sure all old pieces of old rope seal are removed from engine block seal groove. Pipe cleaners work good for this. Clean rope seal journal surface and groove of any foreign material. If seal journal is not smooth or excessively worn, a new seal will not cure the leakage problem. Check the rear main bearing for excessive wear with plastigage. If wear of the bearing is excessive and a new rope seal is installed it will still leak. If engine has recently been rebuilt and numerous rear main bearing seals have been installed without success, crankshaft main journals may have been ground off center from the center line of the crankshaft causing the rope seal journal to become oblong or eccentric causing the rope seal to seal at only the high spot on the journal and nowhere else. To verify if crankshaft mains have been ground off center, install a dial indicator on crankshaft rear main seal journal and rotate engine to check for out of round of journal. Do this before loosening the main bearings to replace the rear seal.

Remove rope seal from rear main bearing cap and clean groove. Use the rear main bearing cap as a jig or mold to form the complete rope seal (longer piece) for the engine block groove. To pull the new rope seal into the groove in the engine block you will need a Chinese finger tool or Sneaky Pete. These are made by Lisle Corp., Cal Van, Performance Tool and others. About 1/4-1/2 inch of the rope for the engine block, if it is long enough, can be trimmed down were the Sneaky Pete or Chinese finger attaches to prevent interference with the seal groove when pulling in the formed rope in the engine block.  The alternative to the aforementioned tools is to use fishing line tied to the trimmed down end of the rope like a fly fishing jig. Thoroughly clean engine block rope seal groove and polish or clean rear main seal crankshaft journal surface for installation of the rope seal in engine block groove. Note: It is suggested that on engines that use main bearing shims, to cut out any shim part that will cover the seal groove area that prevents the ends of the rope or rubber seal to contact each other. 

Lightly oil the piece of rope seal to be used for the engine block groove. Install the longest piece of rope seal in the groove in the main bearing cap and use an extension or socket to roll or form the complete rope seal length in the groove to the approximate diameter of the crankshaft seal journal. The rope seal will have to be removed and repositioned in the cap groove to get a complete form to the length of the rope seal.  A piece of exhaust pipe, tin can, plastic pipe or anything the same diameter as the rear crankshaft seal journal can be used to check the fit of the formed rope seal in the main bearing cap. Warning!! Do not cut the ends off of the rope until the formed seal is installed in the engine block and the loosened main bearings are tightened backup. Take the rope out of the rear main bearing cap and install it in the engine block by gently pulling on one side and pushing on the other side working it in the groove in the block until approximately ¾-1 inch or more is exposed on both sides. Using a flat screwdriver about the width of the rope seal opposite the puller side to work the rope into the groove can aid in installing the rope while pulling it in being careful not to nick the seal journal on the crankshaft. Do not stretch the rope seal when pulling it into the groove in the engine block as this will narrow the rope and it will not seal causing a leak. Tighten up and torque the main bearings that were loosened to drop the rear of the crankshaft to manufacturer’s specifications. This will push the rear of the crankshaft back up into position and set the rope seal in the engine block. The rope may have to be pushed backward or relaxed a slight bit after pulling it in. If the rope seal is pushed too far back into the engine block groove, this will cause excess pressure on the rope seal and the rope will burn from friction causing a leak. Once this is done, trim both sides of the rope seal with a very sharp knife approximately 1/32-1/16 inch of protrusion on both sides. When cutting the ends of the rope seal in the engine block, be careful not to gouge or cut into the crankshaft seal journal face. Install the remaining rope seal in the rear main bearing cap and lightly oil the face of the rope. Form or roll it to the approximate diameter of the crankshaft journal like done previously for the engine block seal groove. Trim the excess off on each end to protrude approximately 1/32-1/16 inch on both side. NOTE: If the rope seal is not correctly rolled or formed into the groove all the way to both groove ends and interferes against the crankshaft seal journal when the main bearing cap is installed, the rope can be pushed down into the groove in both the engine block and the rear main bearing cap. This will buckle the seal in the center causing excess pressure and burning of the rope seal. Form the protruding ends of the rope seal to the center of the seal groove so none of it gets caught between the engine block and rear main bearing cap when installing the cap on the engine.  Failure to do this may cause incorrect clamping of the rear main bearing cap leading to excess rear main bearing clearance which will cause a main bearing knock and seal leakage. Install the bolts in the rear main bearing cap or retainer to be used as guide studs. Place bearing cap or retainer to engine and start bolts in bolt holes a few turns. Push bearing cap or seal retainer straight up until it contacts engine block. Tighten bolts equally to prevent binding of bearing cap or seal retainer in press fit of block (some engines). If silicone sealant was used on the rear main cap side seals or the engine oil pan, allow 24 hours before starting engine to let sealant cure. The most important thing is to keep things CLEAN, take your time and be safe.  Clean and install engine oil pan with a new gasket. It is suggested to use spray trim adhesive or grease if preferred to hold gaskets to engine for oil pan. Lower engine and bolt up motor mounts if previously done. Fill with oil and test.

To replace a rope seal with a rubber rear main seal is done basically the same way. First install the rubber seal half in the main bearing cap groove to check the fit. The seal should fit easily into the groove or have a slight press fit and should not move around (excess side clearance) in the groove.  Bottom out the seal in the groove and apply slight pressure to both ends with your fingers to center the seal in the groove. Then hold the center of the seal down in the groove with you thumb or fingers. The ends of the seal should be at least flush or slightly protruding out of the cap groove. If the seal ends are below the parting line of the bearing cap, then there will be no crush or correct contact of the seal ends when installed causing the seal to fit loosely in the groove and leak. When installing a rubber seal offset the ends of the seal approximately 1/8 to 3/16 inch from the parting line of the block and bearing cap. A couple of spots of RTV silicone can be used in the groove to prevent the seal from rotating if so concerned. Most of the older engines from the 60s back that originally had a rope seal may not have the seal groove machined to accept a rubber seal. This will show up as a full rough casting or partially rough. The rope seal when formed in the groove will conform to this rough casting whereas a rubber seal will not. The outside diameter of the rubber seal will locate on the high spots of the rough casting and allow engine oil to migrate past the exposed outer areas of the seal. Also the inside diameter of the groove may not be consistent to the diameter of the seal journal surface as it is not machined causing high and low spots of contact to the seal journal. If an attempt is made to install a rubber rear main seal in this situation with a rough casting, a light coating of ultra RTV silicone can be applied to the back of the rubber seal or in the groove and the seal can be shimmed up if the groove is too deep. For RTV silicone to work correctly, all areas must be clean and free of oil. Installing the seal in the rear main bearing cap groove is not a problem but installing the seal in the engine block groove can be tricky as the silicone applied to the back of the seal will be wiped off if it contacts the engine block before it is totally installed in the groove. Do not get any silicone on the crankshaft journal surface or use excessive amounts of silicone. Do not cut off the ends of a rubber rear main seal. There are no guarantees this will work just suggestions to try.

For added information on rear main seal installation, look up Best Gasket fanfare page https://bestgasket.com/fanfare/

The problem I found with rope seals with the crank in place was getting the top seal deep enough into the groove at the top. I have always formed the rope into a "V" similar to the groove then worked it in by sliding a hammer handle from the ends towards the centre leaving the rope at a slightly smaller radius than the crank journal before trimming the ends just above the bearing cap face allowing for some crush on the rope but not enough to spread it between the cap faces. By doing this I have not had excess bearing clearance or a leak.

Tony