The Stovebolt Site Forums The Shop Area Engine Shop Rear Main Seal - Can't get crank to drop

I decided while I was doing some other work to see if a new rope seal would slow down the rear main leak. There was a neoprene seal that had been leaking for several years. I removed it and cleaned up the surface of the crank under the old seal with 600 grit paper and flushed it with carb cleaner. I have a new Best Gasket rope seal to install. I plan to pick up a Sneaky Pete tool tomorrow. I've loosened the other main bearings 1-2 turns but I can't get the crank to drop any at all even with prying. Any suggestions? Looks to be difficult to get the new seal started without a little extra clearance. How much can it move without damaging the front seal and the transmission input seal?

If the rod caps are still installed, you'll just have to pry harder to overcome the piston ring resistance. 1-2 turns on the main bearing bolts isn't really that much.
If you loosen the rod caps too, you should be able to get it to move.

Loosen or remove the transmission-to-bellhousing bolts. You might need to move the transmission back a little to let the bearing retainer clear the hole in the bellhousing. The crank can drop quite a bit at the rear without damaging the timing cover seal. I'd loosen the main bearing bolts 1/4" or so.
Jerry

I forgot about the transmission input shaft. That would restrict it from dropping down.

Thanks, I knew there was something I was missing.

I’ve done this job on my GMC 270. In my honest opinion it’s best to lower crank even from front to rear. I removed the radiator, crank pulley, dropped torque tube, and removed the transmission. Then it’s very easy to lower crank and remove the rear main seal. I also used the best gasket brand rope seal. Pack as much of it as possible in the block side to make sure it’s fat in the block, to make as much contact with the crank shaft surface as possible. Same on the bearing cap side. I used RTV lightly on both the bearing cap and block surface. I snugged it down tight. I let it sit overnight and then raised the crank back up the next day, torqued the caps and then put it all back together. Little to no leaks.

You should be able to get the top part of the neoprene seal out without dropping the crank. Have you tried pushing on one end to see if it will rotate out? Just asking, because a lot of the guys here seem to be inclined to replace the better two piece neoprene seal with a new rope seal.

Was the neoprene seal leaking because it was installed in a motor that was not machined for a two piece seal? For example, the 56 235 was the first year for the neoprene seal and the 55 and earlier blocks cannot be retrofitted because the machining on the rear main cap is too deep for the two piece seal and so you have to use a rope seal.

The other thing is that the rope seals of yesterday had an asbestos component to them. Today’s rope seals are a fiberglass graphite and do not work as well and are prone to leaking themselves. Not every Installation mind you, but quite a few.

If your block is machined to accept the two piece seal, which is an improvement by the way which is why gm switched over, why are you going back to a rope seal? No criticism here mind you, just couriosity.

It seems Mike above is suggesting the neoprene seal is better and if that's what he's saying I agree with him 100%. I found some very old rear main seals in the attic last year, but I'm not sure they'd still be ok to use. They've been there over 35 years. I think they're the old asbestos fiber seals, but I'm not 100% positive. They would have been bought in 1977. I used the neoprene seal in mine...when I got the engine there was no evidence it had ever been disassembled and it had a neoprene seal when I took it all apart. It also showed evidence of leaking, so I compared the seal I removed from it with a brand new one. You can see what I found in the attached image. The edge on the new one sticks out 1.1mm further than the old worn one, so it shows this seal wears out over time. Was that enough to let it leak? I'm certain it was. Here is what I did and it has worked for me:
1. I cleaned up the crank area which rides on the seal with 600 followed by 1000 grit sandpaper until it was nice and smooth.
2. I cut strips of self-adhesive foil tape until I could tell the thickness was going to push the seal out of the groove by .006~.008. This as I recall was two strips laminated on each other. I wanted to be sure the new seal made decent contact with the crank surface. Using a 1/2" piece of common copy paper (.004" thick) I could tell the new neoprene seal didn't fit quite closely enough without shimming it a bit. In other words, that piece of paper didn't have much resistance.
3. I cleaned the back side of the new neoprene seal and applied those strips carefully to just the bottom part...not the part on the sides of the seal. Then I checked to be sure the metal rod inside that neoprene seal wasn't going to be sticking out too far now. Turned out I needed to grind a tiny bit off both ends of one seal piece using a Dremel tool and a very small bit.
4. Then I assembled applying some aviation gasket sealer to the part of the seal that fits in the groove. No leaks now.

Oh and one other thing that hasn't been mentioned yet but I think should be said: the better your main bearings are (the less slop they have), the better job your rear main seal will do. Oil is going to be coming out there in all conditions but less is better than more and the 235 leans back at a pretty good angle, you know.

The full circle seal I suggested has a lip that will accommodate a "Speedy Sleeve". The specifications on the seal state that it will expand up to .015" oversize from its nominal diameter of 3 7/8". A worn crankshaft seal surface that does not give the rear seal a smooth area to run on could probably benefit from a repair sleeve, which is stainless steel, and far more wear-resistant than the original crankshaft material, IMHO.
Jerry

Side question on the Speedy Sleeve. Why doesn't the oil leak between the crank and sleeve?

Dennis

Speedy Sleeves are a press fit on the crank, so there's essentially no space for oil to get thru (unless there's a big gouge in the crank that goes the full width (length?)of the sleeve.) Some installation instructions say to put some sealant on the inner bore of the sleeve.

I got the upper half of the old neoprene seal out very easily by pushing on one side with a small pin punch enough to grab with my fingers on the other side and pull out. It slid out easily. The sealing surface on the crank was not smooth which is why I cleaned it up with some 600 grit, still not perfect. My hope was that the larger sealing surface on the rope seal would leak less. Removing the crank and doing a better repair is not something I want to do right now. I'll be satisfied if I can get the leak to a few drops at each shut-off. I haven't checked the main bearing clearance. I'll have to look and see if I have any plastigauge.

I've had this truck about 12 yrs and do some work on it about every other winter but somehow never thought to check the engine S/N. Looked it up yesterday, the block is a '47 block in this '41 truck. I'm assuming from that, that it is not machined for a neoprene seal.

I have a T-5 transmission with an adapter and the top transmission bolts are socket head cap screws. The top right is very close and my socket got stuck so I had to remove the floor and the hand brake lever to get it loose. Yesterday was grocery day and today was gardening day, hopefully I'll get back in the shop tomorrow.

Most good quality speedy sleeve kits come with a small vial of red LocTite and a driver included in the kit that helps lock the sleeve to the surface and assure that it's leakproof. Red LocTite has to be heated to 500+ degrees F. before it breaks its bond, so there's no danger of it coming loose on a stovebolt crankshaft hub.
Jerry

Thanks for the explanation guys.

Dennis

I hadn't thought of a speedy sleeve, I used one successfully on the rear axle pinion shaft. Now I'll have to decide if I want to "do it right" with some extra work or try the seal with the "cleaned up" crank surface.

The crankshaft needs to be out of the engine to get the sleeve installed properly. That's not something you want to try on an "in the block" seal change. I'm also not really sure there's enough room for a sleeve to work without doing the machining for the full circle lip seal. It's something to consider doing the next time you do a full rebuild, however.
Jerry

Correct on the seal. Two piece are better, but can only be used for the 56 and up blocks. You have a 47 block which is probably why it was always leaking. So you will need to install a rope seal. Truth be told, I have never attempted to do an in car rope seal install although I know that back in the day a mechanic worth his meddle could do it.

I've done dozens of them, with about a 75% success rate. There are bunches of "shade tree" tricks the purists here would scoff at, but they worked well to put groceries on the table and pay the rent, and the customer got his vehicle back without a leak most of the time. There's even a way to put the bottom half of a new rope seal in, and tighten the top.
Jerry

I have done both of my 216 rope seals with the motor in place. I used the Best Gasket rope seal. In both cases I removed the transmission and adjusted the main bearings down to minimum clearances. Both were successful. However I tried several times with the 51 without adjusting the bearings and they failed after about 100 miles. I think the crank moved around to much and pounded the seal flat.

Learned that from my first boss. Most the time in the rig it seemed best to do it that way. At least it slowed down the leak, which was often a better result than after messing with the upper.

Slow frustrating day. Finally found I had put in an extra bolt in the hand brake bracket thru the adapter plate. After removing that I put longer bolts in the transmission and the transmission slid back easily and the crank drops easily. The Sneaky Pete I got is a NAPA one (they had it in stock), doesn't have the Chinese fingers to grip the seal but a metal clip. I looked at the Lisle website and their picture has the same metal clips. The clip is about the same size as the seal opening. When I clamp it over the end of the seal there is too much material to get started into the groove. Doesn't help that the ends of the seal are frayed. I tried trimming off some of the frayed end but still didn't help get it started. Current plan for Monday is maybe to try rolling the seal out thinner or trying a wire looped thru the end.

Roll the seal in some clean motor oil, and thin it out by rolling it on a clean, smooth surface like a piece of glass. I've coaxed a seal into place at times by using the wire trick, and once the wire is snaked over the crankshaft, turn the crank while holding onto the end of the wire. Slow and steady- - - - -don't get impatient!
Jerry

The thin strip of stainless steel that retains the rubber in a windshield wiper can be slipped between the upper rope seal and the engine block to push the rope tighter against the crankshaft. Combining that procedure with a new piece of rope seal in the main bearing cap solved a lot of leaks back when I was fighting the flat rate as a line mechanic.
Jerry

I used picture hanging wire to pull it around. I did not rotate the crank. The first half inch is the hardest. I use the gooey Lucas oil supplement to lubricate the seal and guided the initial bit with a screwdriver.