Thanks Art and Jay! This is a compilation of some earlier work.

I hate an oil leak. It is embarrassing, frustrating and just plain messy. One of the worst oil leaks on a 1949-55 Cadillac motor is the engine rear main bearing seal, a repair job that intimidates many owners. I know, I suffered with this leak in my 55 Series 62 Sedan for about 12 years because I didn’t want to take the engine out, but replacing the rear main seal CAN be done correctly with the engine in the car.

The engine in my ’49 6107 Club Coupe was carefully rebuilt recently with the installation of a Teflon-impregnated rope rear seal, which after 500 miles started to leak. The oil pan also seemed to be leaking for two additional reasons: 1. the bolts were slightly loose, which typically occurs after the engine is put back in service and the engine heat shrinks the gasket; 2. the rear pan gasket had been made out of silicon liquid instead of the original cork strip, and it came apart. I repaired everything without removing the motor and it seems to be holding perfectly — no more drips on the driveway! So here is my recommendation on how to proceed:

1. Buy a neoprene (rubber) seal from Terrill Machine in Deleon TX, Olson’s Gaskets in WA or from one of several other Cadillac parts vendors that sell them. Do NOT use a rope seal. Some guys are good at installing the rope seal, but the installation and trimming of the rope to just the right length is CRITICAL. Instead, the modern-style rubber seal provides a true dynamic lip seal and the installation is more idiot-proof. Also buy a quality oil pan gasket set. I like the “BEST” brand for these types of parts instead of FELPRO. Olson’s carries them.

2. Drain the oil, then use a lift or jack the front of the car up relatively high, preferably putting the front wheels on ramps (be sure to chock the rear wheels or put the rear of the car on jack stands);

3. Remove the 2 bolts in the frame holding the idler arm on the passenger’s side of the steering links and lower the center link. Remove the exhaust crossover pipe;

4. Disconnect the battery ground cable and remove the starter (heavy!). To do this, unscrew both of the small wires that attach to the solenoid, noting which one connects to which terminal. Place a rag on the frame rail and rest the starter on it. The positive cable will hold it there satisfactorily, so there is no need to undo any of the other wires;

5. Remove the oil pan and the lower flywheel cover (heavy) to provide working room to get at the seal. Inspect and repair any “dished” bolt holes in the pan — the oil pan surface should be flat. Often, when an oil pan or valve cover is leaking, some ham-fisted mechanic or owner will over-tighten the bolts trying to stop the leak. This deforms the pan or valve cover and ensures that it will leak from now on. If need be, hammer the bolt holes flat with a small hammer and a narrow block of wood to act as an anvil. Re-check for flatness. Use a long, STRAIGHT board with a long piece of sand paper to flatten and re-surface the bolt pattern surface, if desired.;

6. Remove the windage pan, the tray-like baffle bolted to the bottom of the block and the oil pump;

7. Remove the rear main bearing cap. Remove or, better yet, just loosen the 3 middle main bearing caps, leaving the front one alone. (Note the direction the middle bearing caps face if you remove them, as it is important to replace them in exactly the same position.) You do this to let the crankshaft droop just a fraction of an inch or so to slightly free up the upper half of the rear main seal;

8. Screw a slender wood screw into one end of the upper half of the rope seal and grab the screw with pliers. Using a brass, wooden or plastic rod (in order to not scratch the crankshaft journal), push up on the other side of the upper half of the existing rear main seal, while pulling down on the pliers to draw the rope seal out of the crankshaft journal. Once it protrudes out a bit, you can grab the seal itself and pull it with the pliers.

ART GARDNER DEMONSTRATES HOW TO REMOVE THE UPPER HALF OF A ROPE-TYPE REAR MAIN BEARING SEAL WITH THE ENGINE IN THE CAR. YOU MUST REMOVE THE OIL PAN AND REAR MAIN BEARING CAP, LOOSEN THE 3 MIDDLE MAIN BEARING CAP BOLTS AND SCREW A WOOD OR SHEET METAL SCREW INTO ONE SIDE OF THE SEAL. PULL ON THE SCREW WITH A PAIR OF PLIERS WHILE PUSHING AGAINST THE OTHER SIDE OF THE SEAL WITH A SOFT PUNCH AND OUT IT WILL COME.

9. Installation of the rubber seal requires no tools — just slip it into place in the upper half. NOTE: the direction/orientation of the new rubber seal is critical. Follow the directions on this that come with the seal.

10. Install the cork strip in the groove/channel in the rear main cap and trim to length, as shown below. Trim it so that the ends of the cork slightly protrude from the end of the cap in such a way that the ends of the cork strip are parallel to the ends of the cap. You want the cork gasket to have some “crush” to it when the oil pan is bolted up. This is much easier to trim before installing the cap (otherwise, substantial trial and error is required). Although probably unneeded, you can place a small amount of silicone gasket sealant on the end of the cork strip immediately prior to final fitment of the rear main bearing cap against the block (before the silicon has a chance to set). Place the lower half of the rubber rear main seal in the rear main bearing cap and orient it according to the instructions;

11. After coating the lower main bearing halves with oil, replace the main bearing cap(s), including the rear cap, and torque them according to the shop manual specifications. Cleanliness is of paramount importance here.

12. Take apart and clean the oil pump. If the lower plate upon which the gears rest is worn, send the pump away for rebuilding. Unless it is broken, I would retain and re-use the same oil pressure regulator relief valve spring, since some rebuilders install a stiffer spring which would increase the oil pressure excessively and maybe cause more oil leaks! Before replacing the pump, fill it with Vaseline so that it is primed and will have pressure when you first start the engine. The Vaseline will then melt away.

13. Install the front cork seal, after trimming to length. This trimming is a careful, slow, iterative process of stuffing it in the groove, noting the excess length, removing the cork, trimming it slightly and test fitting it again and repeating as needed until done. Trim small amounts and sneak up on the final trimmed length. Again, you want a slight crush to the cork seal. Also, you want the ends of the cork seal to be parallel to the machined engine block surface. Here, as contrasted with the rear cork seal, you definitely want to seal the ends (tops) of the cork seal with a dab of silicone sealant just prior to final fitting (and just prior to installing the pan).

14. With the front and back cork seals now trimmed and in place, next test fit the side gaskets and trim them to closely abut the sides of the cork gaskets. Use as little silicone sealant as needed to seal the side gaskets to the cork gaskets. Use gasket sealant to hold the side gaskets in place against the underside of the block while you bolt the oil pan in place. Apply the gasket sealant only to the top surface of the gasket, since it will be easier to scrape the gasket off the machined engine block than off the ribbed surface of the oil pan next time this job has to be done.

15. Replace all parts mentioned in steps 3 through 7. When installing the oil pan, torque it to proper specs (10ft-lbs max). Do NOT over-torque or the pan will distort in the vicinity of the bolts and cause leaks.

16. When you start the motor, the first thing to do is make sure the oil pressure is normal. Then check for leaks. After 500 miles, re-torque all bolts, especially the oil pan bolts. Two of the oil pan bolts are above the starter, which will have to be removed temporarily to get at them.

If the engine has a lot of miles, then it would be prudent to replace the main bearings while doing the rear seal (and won’t cost much). If you were going to do more than just the main bearings and these seals, you would remove the engine, but this job can be done with the engine in the car. There is a trick to “spinning” the top half of the bearings out (using a flattened cotter pin inserted in the oil hole of the crank and turning the crank by hand). Taking off one bearing cap at a time, after installing the new bearings halves re-install and torque the bearing cap back on twice: the first time for a preliminary bearing clearance check with Plastigage; the second a permanent installation.

By the way, on a lift this job can be done in 4-6 hours, maybe a good bit less. It took me the better part of a weekend on a creeper since extra time was spent over-restoring some parts (powder coating the oil pan and some bolts, etc). NOTE: A high-quality torque wrench is the key to this job. You probably need two different torque wrenches. A low torque unit for the pan bolts (probably 1/4″ drive” and a stronger one for the main caps (probably 1/2″ drive). The specified torque on the pan bolts (and the valve covers) is so low that there is a substantial risk that you will over tighten them or under tighten them by a good bit if you use too large a torque wrench, with equally leaky results either way. Below is a picture of the rear cap reinstalled, with the cork gasket in place on its underside, just to the left of the flywheel in the right center.