Best gasket's Armin Brown holds a length of the GraphTite seal material. Since original-style seals containing asbestos are no longer available, and substitute seals were trouble-prone, BESTgasket developed this new alternative.
With all the reasons that are usually given for powering a street rod with a vintage mill, there is one glaring shortcoming inherent in many older engines that is often overlooked-but the oil spots they leave on the garage floor aren't. According to Armin Brown, of BESTgasket, leaking rear main seals are the biggest frustration with most early motors.
Rubber replacement seals, if available, may be the cure for some engines that originally used rope rear main seals. But, a rubber rear main seal requires much closer engine machining tolerances when compared to a rope seal, and not all engines can be successfully converted.
The engines BESTgasket has found that can be changed to a rubber seal are:
Buick straight-eight 40-50 series, '34-53
Buick V-8 364-401-425, '57-66
Cadillac V-8 331-365, '49-58E
Chevrolet V-8 265-283, '55-58
Chrysler V-8 392, '57-58
Ford V-8 312, '56-57
Oldsmobile V-8 301-324, '49-56
Oldsmobile V-8 371-394, '57-58
Oldsmobile V-8 394, '59-64
For many engines engineered for a rope seal, the lack of precision machine work means that simply changing to a rubber seal will not produce the desired results. Asbestos rope seals were very forgiving in terms of fit, but they were discontinued in the mid-1990s, and the initial non-asbestos replacements that followed were very difficult to trim and did a less-than-stellar job of sealing. As a result, rope seals developed an even worse reputation than they already had. In response, BESTgasket introduced GraphTite rope rear main seals, made from braided PTFE (aka Teflon) fibers with graphite. The sealing results are remarkable and the installation is simple with easy trimming. The rope material is highly conformable, filling in any seal housing inconsistencies. Its naturally slick surface places less drag on the crankshaft, allowing for detection of other "hang-ups" during the engine build.
As the Ford 312 Y-block is a popular vintage engine, and it's also one of the most problematic engines when it comes to leaky rear mains, we asked Armin, along with Ted Eaton, to demonstrate the proper installation of a GraphTite seal. The same general process can be followed for other engines, minus the roll pin installation.
Ford 312 Y-blocks (identified by seal retainer stamping "ECZ") have a unique problem not found in most other engines. The seal housing area in the block and lower seal retainer is very shallow-compare the 292 retainer on the left to the 312 on the right. Most engines have a deep V-groove to house the rope seal, holding the rope firmly in place. Being shallow and without the V-shaped recess, the 312 rope seal can grab hold of the crankshaft and spin, ruining everything. This can happen most often on initial start-up. | 
A 1/16-inch hole is drilled in the bottom of the seal retainer directly above the casting brace. | 
As a preventative measure, BESTgasket includes a 1/16-inch roll pin in its gasket kit, which gives the rope something to grab onto. |
The roll pin is then pressed in, leaving about 1/8-inch showing. With a prick punch or nail, open a small hole on the backside of the lower rope seal to be placed over the roll pin. | 
Press the rope seal into the retainer. (Do not presoak GraphTite rope seals in oil.) Use a smooth socket extension or box wrench handle to compact and flatten the rope seal inside the seal retainer. The rope might fan out slightly around the pin, which is not a problem. | 
Included in the kit are a trimming knife, a trimming gauge, and a wood stick to keep your thumb from being sliced. Trim the rope about 0.015-inch proud using the gauge. Slice through the rope and slightly into the stick to ensure a clean cut. Press protruding ends down flush, pushing any loose strands toward the center of the rope end. Perform this trimming process at both ends of the rope. Repeat the above process, minus the roll pin, for the rope-seal-to-block installation. Apply red assembly lube to the rope seal and seal journal surfaces, keeping the rope ends dry. Do not use any sealant at the rope ends. Drop in the crankshaft. |
There are two types of side-seals on the market: black with a steel expansion pin, and orange seals that do not use the pin. Either work well, but BESTgasket is in the process of changing over from the orange style to the black style with pin, based upon customer preference, as the orange can be a bit trickier to install. For installation of either style, it is helpful to slightly chamfer the block edge where the block meets up with the two sides of the seal retainer. This keeps sides from catching on the edge of the block. Apply a thin coat of sealant to the seal retainer to block mating surfaces, but keep the sealant off of rope ends. | 
When using the black side-seals with expansion pins, place the seal retainer over the crankshaft and hand-tighten the bolts. Place a blob of sealant at each side-seal opening. Insert and push in each side-seal, and then drive in the expansion pins alongside the narrow (inner) side of each side-seal. The pins are shorter than the side-seals and must be driven in beyond flush with the retainer surface. Trim the side-seals flush with the retainer surface. | 
The orange silicone side-seals do not require expansion pins, but must be installed at the same time as the retainer. So the seals grab the cap and slide against the block, use oil to coat the wider "block-side" of each orange side-seal and the block surface where the side-seal will rest. (Don't use sealant, as it will destroy the "grab" factor.) Place side-seals into the grooves in the retainer so they are 1/16-inch above flush. Then, pinch the side-seal ends to get them started while sliding the retainer into place. |
It's helpful to chamfer the edge of the block to help the seals start and to use long guide-bolts to help make sure the retainer is going in straight. Make sure orange side-seals bottom out against the block; they are the proper length for Y-block engines and will not need trimming. If either side-seal is sticking out beyond flush, there is a problem-start over. | 
Torque the bolts to spec. Apply sealant around all the seams between the engine block and the seal retainer. Notice the two studs in the retainer used to fasten the oil pan. The studs should be threaded into the retainer with thread sealant. If studs are missing, it's acceptable to use capscrews, but when the oil pan is being assembled, use thread sealant on them to avoid leaks. Assemble the oil pan, and so on, and allow 24 hours for the sealant to cure before starting the engine. | |