Inliners International Forums General Discussion Engines Rear Main Seal Leakage

I have a modified 261 installed in our '40 Chev convertible. Mods are cam, headers, Holly "Pro Jection", HEI, PVC system, 848 head with port work, .080 bore with forged pistons to 9.5 to 1, balanced. Engine runs great, pulls like a mad mule but....leaks oil out the rear main to the tune of a quart every 500 miles with oil all over the bottom of the car!!! I started with an old (years old gasket kit) rope seal and it seemed to go pretty well for a few thousand miles, then began to leak worse as time went on. I pulled the pan and installed one of the new style rubber lip seals and that made it worse than ever! What do I do to stop or at least make the leakage liveable? I was told that the old style rope seals are different than the stuff being made today...any thoughts on that? Thanks for the help.

After I assemble my 261, I had a tremendious oil leak after the maiden voyage. I also changed the seal from a rubber lip, installed by my assembler, to a rope. It was OK for awhile, but started again. I checked the valve cover gasket at the rear and resealed the cover with General Moters gasket coumpound, which is good stuff. I thought I had it. It leaked, I tightened the valve cover hold downs. It still leaked. Finally, I found it! This may be your problem - the pins on the end flange of the crank shaft that correctly line up the flywheel were under size and one was gone! The oil was going out that hole and and at the other two pins and gave all indications of being a rear main seal leak. If you don't know what it is, you would swear it was the rear main seal. As I said, this may not be it, but I have talked to several people who have had the same problem and when they checked, that was it! Good Luck!

By the way, Presten, I like your engine!

Dear Preston;

Tell me how that Holly fuel enjection is working out. I am planning one on a Clifford intake for my 278".

Also that rope seal (Buick) is available from Langdon's Stovebolt. I think there $10 plus S&H etc.

John M......

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Presten,
Not that this is you problem ..and I dont know if the 230 is the same... but I had a leak that I thought was a rear main seal. What was leaking was the freeze plug like cap at the cam. My leak was not as bad as yours.

Clyde

I've got a question for you about the seal surface on your crank: is it smooth or does it have diagonal grooves in it across the part that rides on the rope seal?

If it has grooves, you may have to use a rope seal. The rubber seals will get the lip ground off very quickly if it's not designed for the grooves. If the surface is smooth, then you can use either type of seal.

Keep in mind that your rubber seal can rotate in the groove, just like a spun bearing, and open up on one side or the other. The seals rely on friction to keep still against the crank trying to rotate them. What may be needed is to install a very small pin in the bottom of the main cap. The early 289 Fords had such a pin, and your machinist should be familiar with them.

And yes, I agree with using a Buick rope seal. They will work in just about any engine that uses rope. You may have to remove the crank to install it though, as they are pretty thick. The proper installation technique includes using the side of a piece of pipe to tamp the seal down into the groove in both the block and the cap.

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David
newbie #4153

Correct me if I'm wrong, but I thought the 261 blocks were designed from the factory to use neoprene seals? Did you pre-lube the seal before installing the crank? Running it dry will kill it fast.

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1950 Chevy pickup with '62 261, 4 speed.

Make sure the rubber seal gets installed in the proper direction.

What year 261?

Guys if you are using a rope seal make sure you don't cut it off to short or it will leak after a few hundred miles. Many people today don't know how to install rope seals. Many heavy duty truck engines used the pin mentioned above, this couldn't hurt. Had a guy bring in an engine once that wouldn't hold a rear seal after he had paid to have it overhauled, when we checked it out we found that someone had turned the seal area down when they turned the crank. An old fellow in the shop took a new seal and put a length of wire in the new rope seal. installed it and as far as I know it may still be holding oil and that was froty years ago. They used to do a lot of things that would be laughed out of the country today,but a lot of them worked. Lack of money was the mother of invention, any thing that might work beat walking.
Big Bill