The Stovebolt Site Forums The Shop Area Engine Shop Rear Main Seal

Where exactly is the rear main seal located? Thanks.

It's held in by the rear main bearing cap under the oil pan. You gotsta take off the pan and drop the crank to change it.

Drop the crank? Isn't this the seal that you can get the two halves in with a special tool without removing crank?

Depends on engine, which wasn't exactly specified. The 216-235-261 engines use either a two piece rope seal or a two piece neoprene seal. Either can be replaced without removing crankshaft. Just remove oil pan and rear main bearing cap to access. Changing the rope seals used in '55-earlier 235s requires a special tool, available at NAPA.

Now V8s are a different story. Most SBCs used either a one or two piece seal. May have to pull crank or tranny to change the one piece seal in a small block V8. I don't know for sure because when somebody says "rear main" and V8 in the same sentance, I try to blend in with the wallpaper until I can make my escape.

good luck

chip

During my rebuild of my 216, I decided to try the procedure given on this site, for changing the rear main seal, forcing the crankshaft down slightly. I found that I could not create enough clearance to get the old upper half out,with the transmission in place. Also, I have the tool set and I found it pretty useless. The threading tool instructions call for 3/4" of the rope seal to be inserted in the tool, and this would ultimately be pulled out the other end. However, the seal was only 1/2" longer than the groove and thus too much of the seal would be pulled through. I ended up removing the crankshaft and rolling the seal in. However, if the transmissionis were removed, there would be no problem creating the clearance to remove the old one and thread in the new one.

Well, duh, the transmission input shaft holds the crankshaft up by the pilot bearing. Unless the tranny is hosed you won't get enough wiggle.

4ontheFloor,
if you look in the tech help on this board, you will find an article saying that it can be done with the tranny in place. I think there would have to be a badly worn pilot bearing to allow this to happen. Since I had the chance to experiment, I tried it myself.

Yeah, that makes sense.

Maybe you could loosen the tranny bolts and that would provide enough slop?

I was able to change the rope rear main on my '54 235 by just dropping the pan and rear main cap. Now I didn't say it was easy, though.

Here is some information that might be of interest. When I removed the rear main cap, the seal didn't look that bad, quite compressed but still in one piece. It actually didn't leak much. The new seal of course looked like a trapped piece of rope when installed in the cap. About a week later I removed the cap to adjust the bearing shims. The seal was really compressed and the surface looked very hard and shiny. A few hours later, still apart, the seal looked like a rope again. It shows I think that the new seal is quite resilient and that probably explains why a really old seal cannot perform as well.

The old rope seals had the good-ole asbestos fiber, the new ones use something 'safer'. But supposedly the NOS asbestos seals work better. I puzzled for YEARS why the new rope seals never worked as good as the original one.

Reading on this site and on Inliners about rope rear seals, the recomendation is for a new old stock asbestos seal.The new seals are made from a material like fiberglas and don't seem to work as well.When the seal is replaced with the crankshaft in place, the fiberglass strands break as the seal is stretched by pulling and pushing it into place.I've been told you can use a neoprene 2 piece seal on 55 and up 235 engines, makes in truck replacement easier.