351W leak
 

The rear main seal is leaking on my engine. I have had several people say the seal is a two piece part and is easy to change. I have had others say the engine and tranny have to be pulled to change the seal. Is it the age of the block that determines what needs to be done? Are all 351W blocks the same regardless of age? Help, I am a little confused!

SkipB

Are you sure it's the rear seal? The thing about the Windsor engines is no matter where the oil is leaking from, it looks like it's coming from the rear seal. This is from personal experience as well as advice from others.

There are several possible sources of oil leaks at rear of 351w
1. rear valley corks of intake manifold
2. oil gallery plugs at rear of block (3)
3. Large core plug at rear of camshaft bore
4. Sump seal around rear main cap
5. Rear main cap if sealant has not been applied between cap & block
6. Rear main seal- if two piece type- three likely causes, 1.ends of seals should be staggered in relation to cap parting line. 2. pin or hole for use with 'dogs turd' type rear seals, if this pin is not removed or the hole for it not filled & deburred it will distort the lower seal half at this point. 3. check that drain hole in rear main cap is open, I have seen some come from factory where they have not been opened up enough by the machine work which floods the rear seal.
7. Thread sealant reqd on Flywheel bolts- this is not reqd on early cranks as holes are blind, but later single piece seal cranks may be open and therefore require sealant.
8. Grease or lube should be applied at the crank/seal interface during assy, if its simply oiled and then put in storage for some time prior to startup its not uncommon for the seal to 'stick' to the crank and destroy the seal surface and it will have a slight leak from thereon.

Two piece remove the pan & rear main cap to replace---single piece, remove trans, clutch & flywheel to replace.

They're both right. You need to ascertain the exact source of the leak before tearing anything apart.

Most repair shops have a smoke machine. It injects an oil based smoke into the crank case. Whereever the smoke comes out, is where the oil comes out. Many parts stores sell a flourescent dye. Pour it into the crank case and run the engine for a bit. Use a black light to find the leak.

As to your original question, the answer is yes. Older blocks use a two piece seal. This can be changed with moderate hassle with the engine in the car. Newer blocks have a once piece seal. You have to seperate engine and trans to replace it.

You can easily rule out some of the causes for a leak in the rear of the motor. First, if the rear cork seal of the intake is leaking there will be evidence of oil on the upper rear surface of the block directly below the intake manifold, easy to feel with your finger. If the oil pan gasket is the source, usually there will be oil present on the rear of the oil pan in front of the block plate. A flashlight will help here. If the leak looks like it is coming from inside the bell housing or mainly on the block plate, then it could be the main seal or the flywheel bolts but many times if the flywheel bolts are the source you will have oil on the surface of the flywheel and clutch problems as a result.

Early blocks use a two-piece seal while late blocks use a one-piece seal. Usually it is the two-piece seal that gives the problems. When replacing the two-piece seal, be sure NOT to align the ends of the seal with the joint made by the end cap and the block. The ends of the seal should be offset. To replace the two-piece seal you must remove the tranny to get the input shaft out of the way and then drop the oil pan. Then the main caps need to be loosened to allow the crank to drop down a little. There is a tool available to make removing and inserting the new upper half of the seal easier. The job is easier than it sounds but it can be time consuming.

I agree with everyone else who posted. Spend the time and effort to carefully locate the exact source of the leak before tearing anything down. Good Luck.

Guys,

Thanks to all of you for saving me a lot of time and money!

The engine leak that appeared to be a rear main seal ended up being a leak where the remote oil filter adaptor attaches to the block! All the oil did run to the back and bottom of the engine. We put the car on a rack, cleaned the whole engine off underneath and then watched for the leak to show itself while it ran. The cheap aluminum adaptor was brand new, but it had been overtightened and was cracked. So I ordered a billet replacement. Problem solved!

I also ran a pressure check on the coolant and found a bad thermostat housing. It was also cheap aluminum and it was leaking somewhat too. I replaced it with a cast iron piece and that leak is gone as well!

Now, a nice dry garage floor, finally

Thanks again for all the input you guys gave to me!

Skip B