I replaced my rear main seals last weekend on my 79 F350 4X4 with a 400, The leak was slow and wasn't that bad but the wife was complaining and the kids and stupid dog would step in the puddle and track it in the house.

I replaced the rear two piece main seal almost as prescribed with the exception of dropping the crank. After I removed the #5 cap I had access to the upper seal so I thought I would give it a little push with the closed tip of my needle nose pliers and to my surprise it pushed right out with little effort. I was very careful removing the upper seal making sure I didn't touch the crankshaft surface area with any tools. It was so easy I thought installing the upper seal would be a breeze and it was.... Sort of.

If I had dropped the crank I would have to remove the oil pump so I can get access to the #1 cap with my 1/2 breaker bar as all the Bering cap bolts required some persuading to get them loose and working under a truck with a creeper on a smooth surface isn't easy.

I got the new upper seal started but since I didn't drop the crank the fit was pretty tight and I started to shave the block edge of the seal. I had it soaked in oil already so I dabbed more oil on it and proceeded carefully but I don't think it was careful enough.

The lower seal was very easy, just pushed it in place by hand. I assembled the cap while offsetting the seals as directed by the official Ford book. The leak stopped for a day or two and now it is leaking a lot more than it used to. All evidence shows that it's the rear main seal again so my question has an rather obvious answer. Was my decision NOT to drop the crank to give me the proper clearance so that I may slip the new upper seal without possibly shaving it the cause of the failure?



The bottom end exposed. No cross member in the way so access was easy.



The #5 Main Bering cap removed.



The #5 Cap and lower seal.



Teaching my Son the fine art (And almost lost art) of auto mechanics. Mom wasn't happy about his pants getting trashed.

 

My opinion, you see how much babbit is missing from that bearing? well your crank shaft is now ridding in that "depression" in the bearing surface. That being said it is pushing downward on the lip of the new seal in a sense "egg shaping" the seal. No tight seal oil comes out. All of the rest of your bearings have to look as bad so the crank is "down" on all the bearing surfaces. I would also venture to say you probably have some leaking at the front timing cover seal But more so at the rear cause the thrust surfaces on the main thrust bearings is likely worn as well so at acceleration your crank is floating back and applying force on the seal lip as well. That motor has to have low oil pressure and certainly some knocking no?

 

Your bearings are shot dude! If the mains are that worn I can only imagine what the rod shells look like.

You didn't dab some silicone on the end seals?

Josh

 

I doubt it's knocking yet, but those bearings are worn pretty bad from the looks of that No.5 main lower.



Most of the wear is on tops and bottoms, very little on sides. That's usually how they do.

You may have a high vol oil pump that's covering some but if it were me .... and it was once on mine .... I'ld change those main and rod bearings while I had the pan off. The beaings are easy to change once you get the pan and oil pump off.

I personally did NOT drop the crank because it's still bolted to a flexplate bolted to a TC that rides in a front pump. In your case, a transmission input shaft is inserted in the pilot bushing / bearing in the rear of that crank .... and it has a seal in the transmission and you don't want it leaking.

Just do them one at a time. Look closely at the crank while you are at it. If you know the sizes, that's "good". In my case I took a main and a rod bearing to the machine shop and they measured the side where they were hardly worn to determine what I needed.

Get those bearings done and the seals will last much longer.

I installed a new oil pump while I was there in my '77.

Beautiful Truck. Junior needs some greasy pants ..... and shirts. Goodwill is a source .... but then .... he has a pair now!.

 

One thing to keep in mind with rear main leaks is that the motor needs to have a good crankcase ventilation setup. The PCV valve needs to be in place plus the vent tube that connects from the oil fill cap to the air filter. I have a pretty radical 514 motor that I just got running, and it had terrible leaks everywhere until I set it up with a crankcase evac setup running into the headers. No other changes, but EVERYTHING was leaking - intake end seals, valve covers, rear main. The damn rear main still drips a drop or two now, but everything else stopped.

You also have to be realistic with the overall condition of the motor. If it has a lot of blow by you're probably never going to get it to stop leaking.

One last thing-------I know you didn't do this, but if the seal is put in backwards it's gonna leak. Ask me how I know.

 

In the photo of my main bearings the dark area is a pool of oil. I did inspect the bearings pretty closely and only noticed what looked like normal ware. I'm not a mechanic/tech just a weekend warrior with lots of good tools and ambition so I don't get to see bearings a lot to make good visual assessment. I have very good oil pressure and the engine never has knocked even on start up.

I just rebuilt the top end of the engine with new heads, Edelbrock intake and carb so I did re do the PCV system so it would work with the new air cleaner. Is there a way to test the PVC system?

Secondly If I replaced the bearings would that mean I would also have the crank turned as well?

 

Maby there is too much crush on the seal ? There should only be around .010-.015 of one end sticking out when the seal is in place. Something that should always be checked.

 

Those bearings are toast bro

Josh

 

I can see that the dark area is a puddle of oil. The problem is all of the bronze that is showing on that bearing. It's worn out!!!!!!!!!!!!!

 

What I circled in red is what everyone is refering to and the indicator the bearings are toast.(Transition where worn into the brass) I guess the bright side is you get to teach your son how to do an engine rebuild.

If you'd remove the crank, put the cap/bearing back on and measure the bore with an ID MIC or Bore gauge you would see the bore is egged shaped. This is the main reason why your seal is wearing and causing leaks.

 

Looking like an echo of what i said in the beging.
I personally would not throw good money into a bad lower end based on the looks of your crank shaft it is as scored up as bad as the bearings.
Find yourself a donor block and build it up swap your top parts over and your back in the saddle.
Want to add though you do have a good looking truck!!!!!

 

I see what you are saying now. Thanks for the info. I will have to think about what my options will be and how to budget for it.

In the mean time I will just have to make this lower end last as long as I can.

 

You dont think his block is salvagable? Cant he have the crank turned and mabe align bore the block?

 

I have looked hard at the crank jornal.



I cropped it and sharpned it and lightened it trying to see better. Hard to say for sure, Il'd have to use my finger nail tester to say for sure but I will say the jornal looks semi rough.

It looks like ridges in it. A good bearing insert will still be grey and show some minor polishing at most. Yours are worn into the copper backing and it shows the ridges cut into it especially well at the transition "DKF" circled.

A bearing shell can be made several ways but the good ones are steel backed for strength, then a layer of copper to provide cushion for the top layer of babbitt. Babbitt is a csoft alloy and composition varies with manufacturer. Your's are well into the copper. Steel shell is next.

Idealy, the bearing and the crank jornal never touch, theye rely on a thin layer of oil seperating them. When surfaces touch, they get roughed up, rough surfaces are harder to maintain the layer of oil. More wear follows.

I have seen cranks that looked like yours, that when a finger nail is drawn across them felt pretty smooth and then a very light bit of polishing in place is possible with a roll of crocuss cloth and oil.

If the finger nail hangs up, catches edges of grooves .... then new bearings will buy some time but they are not going to last.

Have you a friend or aquaintancce that you trust to come by and take a close look at that crank and drag a fingernail across it? You might get by for awhile with a mild polish and new inserts and a HV oil pump .... I say High Volume because you'll need it soon.

I drove my 77 with 4 psi oil pressure thinking that gage was bad home from Ga in '92 and didn't baby it and when I found the truth and replaced my bearing shells and oil pump .... my crank looked better than yours even then. My shells were worn into the copper, but the transition was smoother and didn't show the grooving I see in yours and my crank passed the finger nail test with ease. It still starts at 80 psi cold and holds steady 60-65 on the highway when warmed or hot, and about 40-45 at idle. I was just hoping to get another 20K out of it back then to give me time to get my 400 together. Well, the 400 is on the stand and ready, but the 351M is still getting it done.

If I was to pull it and do the lower end, I'ld have the crank polished, bearing bore checked and if OK, use new bearings to match the crank. I don't like line boring just for the sake of doing it unless it's needed.

How many miles on the motor anyway?


Love the truck!

 

tbear- Thanks for the excellent information. I'm still deciding on what to to for the long term, I'm leaning on building up a new 400 Block and swap out my top end but for now I will baby my engine as it sits now. (Subject to change if money and time permit or I have a brain storm)

I'm going to drop the pan anyway to see if I can slow down my leak so I will take a closer look at the mains and the journal and perform your test. I really don't have anybody else to call on, everybody usually calls me. The last time I did a re-build was back in 1989 with my 79 Super Cab 351M and I had the machine shop build up my core. I pulled the engine and installed it by myself.

I'm not sure how many miles are on my truck or engine. My best guess is 120K on the truck and 50K on the engine and according to the PO he had the heads done but when I replaced the heads I didn't see any evidence of previous work but when I had the pan off I could tell that there has been work done on the lower end. PO also told me that it's on its second engine from the first owner. (I'm number 3)

I have about 5K on the new heads and they seem to be working just fine.

I'll take more detailed photos if I can. The crank is pretty tough to shoot but I'll give it my best effort. Thanks for the complement and good advice.