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Rear Main Oil Seal - Stupid Question of the Day

I never gave up on my wife’s convertible, so I’m in the middle of rebuilding the engine. Original problem was described here:

So, everything’s cleaned up, the crank is in, and I’m trying to mount the rear main seal. So, um… which way round does the seal go? The diagrams from Haynes, Autozone, and the shop manual aren’t clear. The seal is essentially a U-shape. Does the open end of the U face into the engine, or towards the transmission?

The closed “finished” side is to the outside and the concave rubber with the garter spring is toward the inside. Wipe the inner surface of the rubber with oil before tapping the seal in. If a seal installer is not in your tool box a large socket will work. Just set the seal squarely in around the crank, rest the socket against the seal and tap it firmly until it bottoms out.

Thanks. I figured that was it, but I would have hated to be wrong.

Re: large socket. As a summer student I worked in an open pit mine on haul trucks, bulldozers, loaders, etc… Even with the trucks being big enough to fill two barrels with coolant, I don’t remember a seeing a socket large enough to fit this seal. :slight_smile: I’ll be able to get it in with some wood and a mallet.

And now the followup question:

I put a few scratches in the seal carrier when I was taking out the old seal. I’m worried about leaks through the scratches. Would a bit of RTV sealant between the seal and the carrier work here? Can I clean up the carrier with emery paper?

If the seal is already in place, it’s water under the bridge now. If it were bad enough to cause a problem, you probably would have realized it before putting it back together and sought out a replacement part.

I haven’t put it in yet. There’s still time to clean it up or put sealant. Would the RTV work?

If the scratches in the carrier left a raised edge, I would knock them down with a file or some emery cloth. If you have deep gouges, fill them in with JB Weld or similar and reshape the area before installing the seal. Don’t go overboard with the JB Weld if you have to use it. I do not suggest using RTV for this. It could very easily create more problems than you are hoping to solve.


A tiny amount of RTV on the back side of the seal will not hurt anything…Assemble while the sealant is still uncured…

Well, it’s in now, so I’ll be crossing my fingers. The scratches run parallel to the seal edge, so they don’t cross it.

I got a bit impatient last night with the piston rings and didn’t check every single gap. Do people really take the time to do that? The ones I checked were all fine.

Was the block bored to a standard oversize?

No. I checked the bore myself, and the numbers were pretty much to spec. The machine shop also checked it and said it was good. I had them hone the cylinders too. So I’m reusing the pistons with new rings.

The crankshaft does not have a significant wear groove on the journal where the seal rides does it?
If so, this needs to be remedied or the new seal will either leak instantly or start leaking not too far into the future.

The odds are that the ring gaps will be fine but I always check every single one. One single ring with little or no end gap on one piston, some engine heat, and you may end up with damaged goods when the metal expands.

I was afraid you were going to say that. What’s the risk of too much end gap - just poor compression/high oil use?

We thought there was a mild groove on the journal and I brought it in to put a sleeve on it, but when the shop polished it up the groove disappeared.

It’s not a matter of too much ring gap; it’s a matter of what gap there is, if any, disappearing completely when the metal expands due to heat. This can cause ring breakage, cylinder scoring, oil consumption, and even possibly a piston/ring seizue in the cylinder bore.

To be honest, I wouldn’t worry too much about this issue seeing as how you’re dealing with cylinder bores that have some wear and going back with what I assume to be standard bore piston rings. I’m just pointing out that doing a proper overhaul means covering any and all bases.

You should be fine on the seal seeing as how the groove disappeared with some polishing. Some of those grooves can be pretty deep and may require a Speedi-Sleeve to repair.

Moving on to the timing belt - there’s an instruction somewhere that says to mount the belt with the arrows facing out. Well, the new belt (Gates timing/pump kit) has no arrows, so I just put it on. Then I realized that the writing is facing towards the engine instead of towards me…

Does it make a difference? It took four tries to get the belt on without something going off by a tooth, and I really don’t want to try again.

Some manufactures print lines on the belt that align with the timing marks on the engine to confirm proper alignment. These lines only match if the belt is installed in the right direction. If there are no alignment marks on the belt it makes no difference which way the belt is installed.

That settles it then. In my case the marks are on all three timing cogs. Once they all line up with the marks on the engine at the same time I’m all set.