#8 nose bearing?

[carrerarsr65]

is there any kind of maintence or cleaning and greasing that can be done while I have the cases split? to the #8 bearing, what type of grease if any.

[jwasbury]

replace the o ring. you may elect to use some type of sealer goo when you reassemble the cases, although I have read differing opinions on that.

grease? I dont think so. The #8 bearing get oil supplied under pressure, and is one of the routes that oil follows to lubricate the rod journals.

[SCrescue]

Pelican Parts.com - How to Rebuild and Modify your Porsche 911 Engine

If you haven't already purchased Wayne's book, I highly recommend it. The #8 bearing requires very specific sealants and installation prep as indicated in the book. And depending on mileage and condition, it should be replaced with a new unit.

[quattrorunner]

This is a sensitive subject for me. I would seriously consult a pro on this part of the build. I followed the book and have a leak there and that can't be fixed without re-splitting the case. I did NOT use a sealant there, only the o-ring. I believe you should use some sort of sealant and I would ask someone that has done many engines before. Also post this question on the engine building forum.

[KTL]

I would just clean the bearing with solvent but be very careful not to use anything abrasive on the sealing/contact surfaces. If you have access to a bore gauge, use it. It will let you know the condition of the bearing, which I bet is still good to be reused. Measurement of the bearing ID and crank journal will give you a clearance. If you're within spec for clearance, save your hard earned money and reuse that expensive bearing!

With respect to sealing difficulties, I agree the #8 bearing insert should be treated carefully to ensure it sits in the case bore cleanly. Very important to ensure that bore and the bearing contact surface is very clean and has no scratches.

Also don't get crazy with the sealant if you choose to use it. Use a very thin coat to avoid excessive squeeze-out of the sealant. Two cautions about thickness of sealant: 1) fat sealant can cause slight eccentricity of the #8 insert relative to the case main bores 1 thru 7. That means your #8 journal would be oh so slightly offset within the bore of the bearing insert. 2) if you have excessive squeeze-out, you are partially blocking the oil feed hole in the case bore that feeds oil to the #8 bearing insert!

It can be installed w/out sealant and not leak. The key is to ensure the o-ring doesn't get pinched when joining the case halves. I have used silicone paste (o-ring lubricant, NOT the dreaded generic RTV silicone sealant) for lubing the o-ring to make sure the ring can seek a happy place & not get pinched by the case halves as they're bolted together. Also the orange 574 and the Threebond 1211 are good choices for sealing the #8 bore area.

I think the key to success is firmly tapping that end of the case with your rubber mallet to ensure the case envelopes the bearing insert cleanly. Then when you begin your tightening sequence on the perimeter of the case, after you've tightened the main through-bolts in sequence, you should start at the #8 bearing. This ensures you're getting good clamping around that large bearing insert.

Originally Posted by SCrescue

And depending on mileage and condition, it should be replaced with a new unit.

Actually the #8 bearing insert is a very robust piece. Measurements of old, used #8 bearing inserts compared to a good quality new insert indicate virtually no wear. I'm of the opinion that a lot of people tend to replace the #8 as a matter of good practice, when in fact they can reuse it.

The bearing may visually show wear but that is misleading. The silvery coating on the bearings is soooooo very very thin and fragile that it swipes right off. When I measure the ID of the bearing with my bore gauge, the slight (and I do mean SLIGHT) pressure of the gauge anvil and pivot make what looks like a pencil mark on the bearing surface. But it's so slight that you can't even feel it with your fingernail, nor can the bore gauge even detect it.

Just my opinions, so take them for what they're worth.