Imo000

When replacing the rear main seal on an S4. Does the front of the new seal has to be flush with the engine block or will it go in until it bottoms out? Looking at the workshop manual, looks looks like there is a machined step that the back of the seal will bottom out to but this leaves the new seal around 1.5-2mm passed being flush with the face of the block. The old seal looked flush when it was removed.

IrishLegend

I may be doing this on my OB before long.

blown 87

If the crank does not have a grove worn into in where the old seal rode, install it to full depth with the installation tool.

Many factory tools have a spacer that is to be used in places where you need to have the new seal ride on a area that is not worn.

The 928 cranks seem to be very hard and do not suffer from seal wear and no spacer is supplied with the tool.

I recommend using the factory installation tool, not a piece of PVC pipe.

A lot of folks have bought the tools for installing seals, so you should be able to borrow what you need, or call your 928 parts person and buy your own.

Never, ever, hit a seal with a hammer directly on the seal, even to "Just start it".

blown 87

I thought yours "popped" out?

If so, you need to install a new one before you drive it and make sure you are not building pressure in the crank case.

Imo000

I've used the old seal as a driver so the new one never received a single hit from a hammer. However I was expecting the new seal to bottom out at some point (like it does on every other kind of engine I've ever did this on), but it just kept of going and this supprised me a bit. It's about 1.5mm passed the face of the block now and haven't yet bottomed out. It should very soon but before it does, I want to ask others, with first hand experience, what their take is on this.
The old seal looked original from '89 and was flush with the block. It was in there tight so I don't think it migrated over time, but you never know. It could have when the engine was warm and the block expanded.
If the factory setup is to have the seal bottom out, then I'll drive it in untill it does.

Shark_Week

just performed this yesterday. i installed flush to the crankcase and called it good. cleaned the crank and there was no grooves or wear spots . i don't think the idea is to drive the seal till it bottoms out

Imo000

Can you please elaborate on this?

Shark_Week

there is more "room" in the crankcase for the main seal than what is needed. if you installed the seal flush with the crankcase but the sealing lip ended up on a less than perfect surface of the crank than you should drive it in more, to a better part of the crankshaft. as someone noted these cranks wear really well. i think it's more important to keep the rear main seal perpindicular to the crankshaft. keep the seal lined up evenly all the way around the crank so the spring has equal tension all the way around

Sueden

Having just done this twice I know that you drive it in until it is in past flush ! The first time it was flush and it still leaked , had to go back in and knock it in some more that sucked.

AO

I was there with Dennis on this. The problem with leavin it flush is that it will leak at the cutout on the block (presumably the cutout is there to dig out the old seal). When the seal is flush, the rubber portion of the seal barely touches the cutout. Needs to be 1-2mm past flush to properly seal.

Imo000

Now that you've mentioned it, I've noticed this when pulling the old seal last night. As soon as the seal moved, a pool of oil (that collected between the seal and the machines back lip of the block) started to leak out. I was suprised how little the seal had to move for the leak to occur. It was less than a mm, probalby about half.

And yes, the cut out is only there to remove the seal. It's a nice touch by Porsche as all the other engines I've worked on didn't have this and removing a rear main seal was a little more difficult.

blown 87

You may get lucky and not have the seal leak, using a old seal to kind of dampen the hammer blows really is not going to do much, plus what are the chances of it being in straight?
If it is crooked it will not give you the service it should or just leak out right.

When I said drive it in until it bottoms out, I was talking about using the factory seal tool, it has a lip that puts it in the right spot and SQUARE.
I was not saying drive the seal in with what ever you had laying around until the seal would go no more.

That old saying, "Use the right tool for the job" may just apply here.

AO

BTW, I've done this job twice now and it still leaks. I'm certain I only drove the seal flush - becasue I didn't know better. Yes, the right tool would have probably cured this, but alas I didn't have it. So I've been living with a leaky/seapy RMS for about 2 years. Looking for a good excuse to drop the clutch and flywheel.

blown 87

I tried this once before, but we need to put together a list of who has what factory tools that they would be willing to lend to persons that are in need.

I mean even as a pro, how often am I going to need a rear main tool or any of the others?

You can get stuff shipped overnight pretty much any place in the 48 states.

Just a thought.

Imo000

I understands what you are saying and we are both on the same page. When the seal bottoms out, it will be square with the crank. I've done this before (using the old seal as a driver) but in other cases, the seal was flush or near flush when it bottomed out. I didn't hammer the $hit out of it either, it went in at a fraction of a mm, in a criss cross pattern. Yes it would have been easer with the factory tool but that still doeasn't asnwer my original question.

My question was the pros and cons of having the seal being flush or recessed against the back of the machined step of the block.