rear main seal

[umpalumpa1985]

Got a '72 f100 390 with a pretty good leak in the rear main seal (basketball sized spot under the truck after sitting just overnight, oil pressure dummy light comes on after about a week and a half, not burning oil). Haven't been working on engines for very long, and this is my first classic truck. So basically what i need is good advice on the best way to go about replacing it. Without pulling the engine, as it's my daily driver, and as a Marine, it's not usually a good idea to not show up to work . Thank you in advance.

[BobbyFord]

First of all make sure it is the rear main and not leaking out the rear of the intake manifold or valve covers and running down the rear of the block. If it is the rear main seal, it can be replace with the engine in the truck but it's so much of a PITA that I always yank the motor out and do it on the engine stand,, that way I can easily replace all of the other usual leaking gaskets. You'll have to unbolt the fan shroud (if you have one), unbolt the engine mounts, jack the motor up and stuff wood blocks between the mounts and the frame. Drop the pan down, reach inside and unbolt the oil pump and let it fall into the pan, then slide the pan out. They make a small tool kit available at your local parts house for removing a rope-type rear main seal (which yours probably has), it's also a little easier to rotate the crankshaft in the direction that you are pulling out the rope seal (once you get a grasp of it). Replace the old stlye rope seal with a newer two piece rubber seal (Fel-Pro BS30138, I believe). Make sure you get the seal groove in the block clean of sludge before trying to slide the new seal in. Saturate the new oil seal with fresh oil, lip-side of the seal faces forward, press the sealing edge against the seal surface on the crankshaft with constant pressure and rotate the crankshaft in the direction that you are trying to slide the seal. Insert the other half of the seal into the clean groove of the bearing cap and install and torque cap to 95-105 ft. lbs. I use Avaition permatex or anaerobic loctite on the clean, dry bearing cap mating surface before assembly. Reverse procedure to finish assembly. Make sure you get the oil pump driveshaft up into the distributor shaft, I use thick grease to help hold it up and in there. I like cork oil pan gaskets, some people don't. Oh yeah, don't forget to drain the oil before you get started
Someone else will chime in; I'm sure that I forgot something.

[umpalumpa1985]

You are amazing. And it is definitely the rear main. I actually just replaced the valve cover gaskets. And that does sound like quite the PITA. Thank you very much for you help, sir.

[umpalumpa1985]

One other (minor) problem. I recently had a carburetor issue that couldn't be repaired with a kit, so rather than spending a couple hundred on a new carb, i stuffed the one from the '71 f100's 302 on it. Now, obviously, on acceleration, the engine is starved and leans out, sputters, backfires, then accelerates fine. My question is, is there any way i could just get a jet kit and go up a few sizes to compensate for it, or no? And am i correct in my understanding that the a/f mixture screws on the front of the carb are just for the idle circuit, and won't affect this at all?

[71PA_Highboy]

As an add to Bobby's explanation, don't forget the pin in the main cap that keeps the rope seal in place... drive it out before you install the cap seal.

hth,

eric