I'll make this as short as possible and cut out the horror i've been through since rebuilding my 390. Sort background; something like 3 rear mains, none lasting mre than a week before developing a leak. My desperate questions: 1) the block came out of a '67 truck(i think), even though ford used rope seals, the typical rubber fel pro rear main should work, right? 2) The other rear main post mentioned neoprene rear mains, could this help? 3) When I put the last rear main in(in truck replacement), the top half slid in way to easy, no resistance. In my mind this points to some other problem, but I had my machine shop mic the crank journals and the mains have normal wear patterns. Any ideas at all would be greatly appreciated at this point, I have a rebuilt 390 that has more power than I could ever need, but also lubricates its own underbody with great efficiency.

 

I don't know about '67 models, but every rope seal I have replaced has taken a LOT of working around to get the upper half to fit. There is a chinese-finger-puzzle type tool that you can get to help pull them thru, and you need it or the other tool that doesn't work as well that clips onto the end of the rope after looping a piece of 'piano wire' over the top of the crank seal surface.
When I did them, I would take the seal, soak it with oil, and press it into the lower cap using a large diameter socket, rolling the socket back and forth over the seal in an attempt to compress it to what would be its normal shape, and then cut it as evenly as possible with the cap before pulling it into the seal groove in the block. In my experience, this was the only way to get the seal in place. I would end up with one end of the seal hanging down, and one end above the rear main split and then cut the lower seal to fit, with one end receded below the top of the cap, and the other raised above the edge. Fit it together, take it down, look for threads that were hanging loose, refit til it would match up without any threads loose. So, if your seal slid in easily, there is something terribly wrong. The seal surface generally had a series of grooves in it, that would tend to pump the oil back into the crankcase when the engine was running. The grooves were almost 'hints' of grooves, that's how shallow and fine they were.
Three things (in order of my best guess) to check: 1) Did you get the correct seal from your gasket source? 2)Did the machine shop check the seal surface diameter? and 3) Did you spin the rear main? 4)Did you plastigage the bearing to make sure that there is not too much clearance allowing the oil to blow out way beyond what the seal can stop?
Good luck.
tom

 

I had the opportunity to do that job twice, in the truck, inside a week. After the first try, it leaked worse than ever. On my second attempt, I took great care to make sure that the nails which hold in the side seals did not cause the seals to distort as the nails went in. This is difficult under the truck (you know this by now). It may help to bend the tips of the nails a little to discourage them from grabbing the seal. I also ensured that those same seals stood proud of the pan rail by about 1/16 - 1/8". I used some good quality gasket maker as sealer and followed instructions carefully. I think it's cured, but remember that oil leakage is one of the FE's many endearing qualities...
Eric

 

Actually, what I mean to say is that I don't remember anything resembling nails on the rear main or rear main cap side seals. What has my brain dropped onto the floor now? I do remember two 'sticks' of fibery stuff that were the cap side seals, and pre-positioning them above the top of the mating surface so that as the cap was pushed up into place, the friction on the side of the block would tend to force them down towards the pan gasket surface. Once I thought I had them in place properly, I would cut them off flush with the bottom of the bearing cap. Was I doing it all wrong? They came with no instructions, so I was making it up as I went along...
Any good hints as to something I could have done different?
tom

 

Steve Christ's book gives good instructions; an old Chilton's is good too. You've seen the rope type side seals - you took them out. The new neoprene ones slide in after the main cap is back in. Then the nails are driven in flush to the cap. Use a carpenter's nailset of the correct size. Instructions differ as to whether the cap should be finger-tight or torqued before the side seals go in. It likely doesn't matter.
Eric