Rear Main Seal (RMS)

[proline]

I'm attempting to change the RMS whilst the gearbox is out. There seems to be two approaches i.e remove the retainer plate or not.

I intended to remove the plate and have already loosened the 6 bolts indicated by the red crosses in the photo but NOT the 4 oil pan bolts shown by the green crosses – therefore no attempt has been made to remove the plate.

If I re-torque the 6 bolts can I now proceed to remove the RMS using a seal puller or is the RTV sealing the retainer plate now compromised and therefore likely to leak?

[GTSBoy]

It will be fine.

[joshuaho96]

29 minutes ago, proline said:

I'm attempting to change the RMS whilst the gearbox is out. There seems to be two approaches i.e remove the retainer plate or not.

I intended to remove the plate and have already loosened the 6 bolts indicated by the red crosses in the photo but NOT the 4 oil pan bolts shown by the green crosses – therefore no attempt has been made to remove the plate.

If I re-torque the 6 bolts can I now proceed to remove the RMS using a seal puller or is the RTV sealing the retainer plate now compromised and therefore likely to leak?

If you haven't broken the seal on the RTV then as long as you retorque it close to the original bolt tension it will be ok. If you tighten further it will squeeze the dry RTV out in a ribbon that will probably not seal as well.

[proline]

"If you haven't broken the seal on the RTV"

Would loosening the bolts have broken the seal given the 4 oil pan bolts were not touched and no attempt was made to lever the plate off? Fwiw the existing RTV does not appear to have hardened and is soft and pliant.

 

I don't know what the original torque was so would have to assume it was as per the workshop manual so 6.3-8.3 nm.

 

Would the safer option be to just remove the retainer plate and re-RTV. My concerns here are:

a) removing the plate because of the dowels and non-existent level points

b) sealing the plate to the oil pan because the seal will be dependent on new RTV sealing to old RTV in the corners (see blue arrows). I've seen videos of people doing this but obviously I don't know how long it lasted.

[TurboTapin]

First time I see "Rear main seal" acronymized as RMS. I had to google it... low and behold it's a Porsche thing. Learn something new every day. 

[joshuaho96]

2 hours ago, proline said:

"If you haven't broken the seal on the RTV"

Would loosening the bolts have broken the seal given the 4 oil pan bolts were not touched and no attempt was made to lever the plate off? Fwiw the existing RTV does not appear to have hardened and is soft and pliant.

 

I don't know what the original torque was so would have to assume it was as per the workshop manual so 6.3-8.3 nm.

 

Would the safer option be to just remove the retainer plate and re-RTV. My concerns here are:

a) removing the plate because of the dowels and non-existent level points

b) sealing the plate to the oil pan because the seal will be dependent on new RTV sealing to old RTV in the corners (see blue arrows). I've seen videos of people doing this but obviously I don't know how long it lasted.

Loosening bolts will not break the seal on the RTV unless you smacked it with a lot of force while loose. If you actually go to try and pull it off you will discover it takes quite a lot of effort to break it loose. Start at 6.3 N-m and work up towards 7.3. Watch the RTV carefully to make sure you don't compress it past the original set as too far and you can break the bond loose and squeeze out the aforementioned ribbons. You want to stop before that happens. It will still seal but not as well, it can start seeping oil as oil works its way through the crevices. I would not try to seal new RTV to old RTV. I'm pretty sure it won't work. You don't need to go crazy with the fastener preload, RTV applied correctly is crazy strong and as long as the fasteners don't just back out it will be fine.

[proline]

Thanks for that.

"It will still seal but not as well, it can start seeping oil as oil works its way through the crevices."

If it starts to seep oil is it likely to be enough to cause any problems - will it be noticeable i.e drips on the garage floor?

What's your preferred method for pulling the seal. I'm torn between screws into the seal and the seal puller in the attached photo. I don't find inserting of the puller through the lip between the seal and the crankshaft a particularly appealing prospect.

 

[Duncan]

Unless you can't access the sump bolts, removing the retainer and doing it all on the bench, then cleaning and reapplying the sealant is probably easiest. You won't get one of those big pullers in with the crank there.

[ChrisW434]

Frenchies Performance Group make a neat rear main seal install tool, if you're not in a rush and want a smooth install...

[joshuaho96]

6 hours ago, proline said:

Thanks for that.

"It will still seal but not as well, it can start seeping oil as oil works its way through the crevices."

If it starts to seep oil is it likely to be enough to cause any problems - will it be noticeable i.e drips on the garage floor?

What's your preferred method for pulling the seal. I'm torn between screws into the seal and the seal puller in the attached photo. I don't find inserting of the puller through the lip between the seal and the crankshaft a particularly appealing prospect.

 

When I let RTV set before doing full torque on my front diff cover it dripped enough to leave drops on the garage floor. That was with finger tight torque to set before tightening to spec. If you torque it too hard you will basically be doing what I did but hopefully less so. Are you doing this in the car? Only reason I can imagine why you are worried about removing the oil pan is that getting it off means dropping the front subframe and somehow supporting 500 pounds of engine without it smashing into your head.

One way that looks promising is to very, very carefully use a small drill bit to only drill the rubber. Do not put a lot of pressure into the drill, let the bit do the work for you. Then put a small screw into it that does not contact any critical surface and use that to help you pull it out like this: 

I recommend using a center punch as well before you drill. If you miss and have it offset don't try and drill anyways, try again and get a clean starting point for the drill bit. You can use a slide hammer on the screw once it's in or a pry tool if you can get the angles right. Do your best to clean out the swarf from the engine once you have it off.

[GTSBoy]

3 hours ago, joshuaho96 said:

When I let RTV set before doing full torque on my front diff cover it dripped enough to leave drops on the garage floor. That was with finger tight torque to set before tightening to spec.

Realistically, that's a chalk and cheese comparison. His RTV will be set off completely squished as a nice thin film that should have changed not at all when the bolt torque was released and changed again not at all when torqued back up. It's not as if the two surfaces actually moved apart. There might have been a tiny amount of internal tension introduced into the RTV, but if it doesn't have enough compliance to handle that, it has no role being used for the things we use it for!

[proline]

2 hours ago, GTSBoy said:

His RTV will be set off completely squished as a nice thin film that should have changed not at all when the bolt torque was released and changed again not at all when torqued back up.

That sounds encouraging. Would the age of the RTV have any bearing on this - I think it may be the original Nissan sealant but as I said above it still feels soft and pliant?

What would be your preferred method for removing the seal with engine still in car and retainer plate not removed?

[proline]

11 hours ago, Duncan said:

Unless you can't access the sump bolts, removing the retainer and doing it all on the bench, then cleaning and reapplying the sealant is probably easiest.

That was my original intention. Do you think on re-istall of the retainer plate it will seal ok to the sump (there is no gasket) because at the corners (indicated by blue arrows in photo above) new RTV will be sealing over RTV?

[Duncan]

Absolutely. That is 100% how I would do it, you are 4 bolts away from making this job a million times easier for yourself.

[proline]

9 minutes ago, Duncan said:

Absolutely. That is 100% how I would do it, you are 4 bolts away from making this job a million times easier for yourself.

That sounds good. I was told by a skyline "expert" that it would leak at the corners but they've been wrong before.

Have you actually done this yourself?

Do you have any tips for removing the plate?

[Duncan]

No, I haven't done this before, I've always changed the rear main when I change the bearings

I do need to do it some time in the rb30 stagea, and that is how I plan to. There is no reason it will leak at the corners, just have a dab of extra sealant there; the whole point of silicone to seal is it retains some flex over it's life.

No tips required, undo the bolts and gently pry it off with a bar or flat screwdriver if it resists. The seal will slide over the crank. When you reseal it don't use too much silicone, a thin (3mm) bead is plenty 

[proline]

8 minutes ago, Duncan said:

a thin (3mm) bead is plenty

Exactly what the workshop manual says 🙂

I don't doubt your advice is correct but I'm interested to know how if you've never done this before you are 100% sure it won't leak - do you know others that have successfully used this approach?

[Duncan]

mate, I understand you want certainty, especially because if it leaks it is box off again to fix.

but in the end, most jobs come down to fundamentals. In this case you have a factory designed, properly engineered  sealing system with a sealant designed to go in flexible, take up the required shape and then set firm but still flexible, with suitable bolts to hold the pressure on the sealant. you don't need to overthink this.

[GTSBoy]

What he^ said.

The fact that rear main seals frequently need to be changed during the service life of the engine and the desire to be able to do it without having to pull the engine/sump is the reason why the seal is retained the way that it is.

Just clean up the corners of where the retainer goes even more thoroughly than the rest of the job before putting the new sealant on.  And as said above, a little extra dab in the corners never hurts.

[proline]

Good enough for me - thanks for your help guys.