Rear Main Seal

[ccford]

I have a 69 f100 with a 302 and it looks like i'm going to have to replace the rear main seal. i've never done one of these before. i'm assuming it will be a two piece seal. from what i've heard, you get the top piece in by rotating the crank and feeding it in.
has anyone done one of these before?
will it work to fix the leak?
any good tips for doing it?

[fordman]

the book says to drop the crank down slightly to get the old seal in and out. becuase of a pin that holds the seal in place the pin holds the seal into the seal area. that pin is on top of the seal area i think it is. i havent done this on a ford. and i havent read up on it in a long time. one person on here (i wont name him) said that he was able to do it without dropping the crank down.

[70_F100]

If you're replacing the seal with a lip type seal, the Ford Truck Shop Manual says that the locating pin is not used. If you're using the "rope" type seal, the locating pin is there to hold it from turning. The pin is located in the main bearing cap, not the block. To use the lip type seal, pull that pin out.

I've been accused of telling somebody that something has to be done a certain way without explaining why (I won't mention any names), so excuse the length of this post. I want to make sure I'm VERY clear in my instructions and the reasoning behind them.

Okay, here's the down and dirty. If you have a rope-type (packing) seal, it's NEARLY impossible to replace it with a similar seal without pulling the crankshaft. Keyword: PACKING (just like the packing in a faucet, the tighter it's compressed, the better it seals) It CAN be done, but it's a PITA. However, there's an old trick to stopping it from leaking. After you have the rear main bearing cap down, take a small, flat-tip pin punch and drive each end of the seal up into the seal bore to compress the seal. (Make SURE you don't loosen any of the other main bearings before doing this, or you'll have a mess on your hands when you try to put it back together!!!) Cut short pieces of the new seal and drive them up into the recesses you've just created. Trim the ends flush with the block. Remove the old seal from the main bearing cap. Carefully work the new seal into the groove, packing it tightly. Once you have it packed into the groove, cut the ends almost flush with the cap. If possible, cut the ends at a slight angle with the longer edges toward the main bearing. Remember, you're trying to PACK the seal, so that extra on the ends tightens the packing and helps seal everything. You don't want much sticking above the cap, as it will hold the cap off the block when it is tightened down, creating too much clearance in the main bearing. Torque everything to spec and replace the pan. This will work as well as replacing the entire rope seal, and is a HELLUVA lot easier!! (Think 1-2 hours versus at least 8-10 hours)

Next option. You have a rope seal and want to replace it with a lip-type seal. Remove the rear main bearing cap. Loosen all except the front main bearing cap. A couple of turns will do, as you're only trying to gain a little clearance. Much more than that, and you run the risk of damaging the front seal in an automatic tranny. Using a small, flat pin punch, force the seal up into the bore on one end. Hopefully, the seal will start moving. You may have to work at this a little bit to break it loose from the block. Once you have it started, turn the crankshaft in the same direction you drove the seal into the block. While turning the crankshaft, use the punch to keep constant pressure on the end of the seal. The tension/friction of the seal against the crankshaft will "pull" the seal out. You may have to fabricate a rod with a slight curve in it to make this happen. The other end of the seal will start moving out of the block. Once it's out far enough, grasp it with a pair of pliers and pull while continuing to turn the crankshaft. The seal should come all of the way out using this method. You can use exactly the same method if you're replacing a lip-type seal, but you probably won't have to loosen the other mains to remove the lip-type seal.

Just to clarify, this is the first time I've posted about this, so it's not me that fordman is referring to, and that makes two people who have verified this. I've done it many, many times, so I know it works!!! Loosening the other main bearings may make it a little easier to do, but it can be done with them tight, especially on an engine that has a couple of thousandths wear on the main bearings, which most do by the time the seal needs replacement.

Replacing the seal is in reverse order of disassembly. First, make sure the seal bore in the block is good and clean. You can use a flexible brush to run up in the bore to remove any debris. Then, spray it good with brake cleaner to get out anything that may be left. Dry it good with compressed air. Put a thin film of oil on the outer surfaces of the seal to make it easier to get into the groove. Making sure you have the lip of the seal facing the front of the engine, start one end of it into the bore, being careful not to damage the seal. Using your fingers, push the new seal into the bore while turning the crankshaft. Work it in until the ends of the seal are nearly flush with the block. Leave about 1/4" of the seal protruding on one end.

Why do you want one end of the seal protruding this much??? It's a trick I learned while working on racing engines that helps protect against seal leakage.

Now that you have the upper half almost in place, put a VERY small dab of silicone on each end of the lower half of the seal. Place it into the block in the 1/4" void you have on one end of the upper half of the seal, again making sure the lip is toward the front of the engine. It's a little tricky, and you'll think you're bending the seal, but you're not hurting it. Next, holding the seal against the crankshaft with your fingers, turn the crankshaft in the direction that will pull the lower half of the seal up into the block. Keep turning it until you have approximately 1/4 of the lower seal in the block, and 1/4 of the upper seal is out of the block. This is about 45 degrees from flush with the block. If the main bearing cap has the locating pin, remove it and discard it. Put the main bearing cap in place, torque it to the proper specs and replace the oil pan. If you've loosened the other main bearing caps, make sure to tighten them to the proper specs.

What does this do??? Well, think about it. The split where the main bearing cap and the block make contact is a natural passage for oil to the outside of the block. There is no such thing as a "perfect" surface, so there are some very small voids between the two mating surfaces. By rotating the seal 45 degrees, the ends of the seal are no longer aligned with this "passage", if you will. If the oil tries to escape through the gaps in these surfaces, it runs into a solid wall, thereby providing the most effective seal possible.

If there's anything about this that is unclear, feel free to post your questions.

[m-mman]

Uhhh. . . . did you say 302???

I would have the check but last time I did a small block they have a one piece seal (a ring) that is replaced after pulling the transmission, flywheel etc. as well as the pan. (Its kinda like a wheel seal)

Gotta check the books but I dont think a small block is anything like a FE.

[papabug71]

Nope, from what I understand the pre roller blocks have the 2 piece seal. Im in the same boat, mine is leaking oil as fast as I can put it in....

[70_F100]

I checked the 70 Ford truck factory service manual, and that's where I got the information.

[BobbyFord]

You can buy a sneaky pete tool and remove the rope seal without dropping the crank and without loosening any other of the main caps. I've used one a dozen times. Early 302's (pre 82) have two-piece seals.

[JEF199]

I just put a 2-piece lip seal in a 302 the other day. I was able to do it by removing the rear main cap and pushing the old seal out. Getting the new one in is tricky I wiped grease on the lip and foamagastet on the outter edge and was able to push it 75% in. Then had someone turn the balancer while I lightly pushed down on back of the crank w/ a long bolt in the flywheel bolt hole. And pushed the seal up in place.

[70_F100]

BobbyFord, you're exactly right. And you really don't have to have the "sneaky pete" tool. Like I said in my earlier post, just drive the seal partially through and grab the other end with pliers. Loosening the remaining caps is usually not necessary once the bearings get a little wear, which they will undoubtedly have by the time the seal gives a problem. On a tight engine, it's not quite as easy. The "patch" fix I mentioned gives great results, too, without the hassle of removing the top half of the seal. I've done it dozens of times, and it will last as long as a new seal.

Jef199, I agree 100% with you. I pretty much said exactly the same thing in my original post. Turning the crank, even when the seal first starts in the groove, makes it slide in easier.

The trick to the whole thing and to getting the best results is to make sure you have the ends of the two halves offset from the joint where the main bearing cap meets the block. I don't think you'll find that anywhere in any service manual, but it definitely works and you don't have to worry about any oil leaks from the rear seal.

Thanks for chiming in and reinforcing what I said in my post!!!

[JEF199]

Sorry 70 F100 I got a.d.d and didn't make it past the second paragraph. But I wanted to state that I had just used this method and it worked for me. I think the book tells you to staiger the seal on the 351 not doesn't say it for the 302 I don't know why though.

[70_F100]

Not a problem, Jef199. The post was exceptionally long and detailed, just to prove a point to someone who told me in a post on another topic that I always came up with things but never explained them, so apparently I didn't know what I was talking about.

I started doing the stagger thing MANY years ago.

I was working with some guys in a race shop, and saw them do it on an engine they were building.

I asked them why in the heck they did that, and when they told me, I really felt like a dumba$$, because it's such a simple concept.

[fordman]

it was probably because the poster failed to back up his answer with the correct answer. and left the questioner without an answer. alot of guys on here do that. always protect yourself with all information you can provide. that stops others from asking questions over and over again. i have seen where this has happened and others have went elsewhere to get thier info.

[loglat]

Since we're on the topic (let me know if I should start a new thread... notice this is my first post =)

I have what I believe is a 360 that I think also needs a new main seal. The replacement is a 2 piece, so is it safe to assume that I can get the job done without dropping the transmission? That has been my assumption thus far. Sounds like most of the stuff in this thread can be applied to my engine. Any differences?

It may be noteworthy that the original transmission was replaced by an NP435. Also, the reason I say I THINK it's a 360 because that's what the VIN number indicates. However, the air cleaner cover has a 390 sticker on it. What's the best way to confirm?

[70_F100]

This should be correct for an FE (360) engine also.

The transmission doesn't matter.

The best way (and only way I know) to verify, without pulling the head, is to measure the stroke. One person I know suggested to use a wooden dowel (1/4 x 18 works well). Remove one of the spark plugs. Insert the dowel into the spark plug hole, and turn the crankshaft until the dowel reaches maximum height (top dead center). Mark the dowel at that point. Next turn the crankshaft until the dowel goes as far down as it will go (bottom dead center) and mark the dowel again. Pull the dowel from the spark plug hole and measure the distance between the two marks, and that will be your stroke.

3.50" stroke = 360 (or 352)
3.780 stroke = 390 (or 406 or 427)

The only way to be 100% sure is to pull the head and measure the bore, but it's 90% sure that you've got either a 360 or 390.

[BobbyFord]

360, 390 rear main seal is the same. No need to drop the trans.
Count the valve cover bolts:
2 bolts: 239/256/272/292/312 (produced from 1954 to 1964)
5 bolts: 332/352/360/361/390/391/406/410/427/428 (FE engine)
6 bolts: 221/260/289/302/351W
7 bolts: 429/460
8 bolts: 351C/351M/400