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Whatís this nut thatís leaking oil on my engine?

1979 911sc engine. Nut on left side of case just up from the oil sump. This appears to be leaking oil so I was wondering if there is a simple way to fix it or not. Thank you for all advice.

Old 07-15-2019, 10:55 AM
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I assume that you tried to tighten it?

If the threads are pulled, there is no easy fix. The case needs to be pulled apart and a timesert needs to be installed.

The other way to fix it is to remove the stud then tap the remaining hole with a 10mm-1.25 tap to about an inch, then put a bolt and aluminum washer in the hole and address it at the next overhaul.

Last edited by dannobee; 07-15-2019 at 11:15 AM..
Old 07-15-2019, 11:01 AM
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Are you sure it isn't leaking from above and collecting there.
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Old 07-15-2019, 11:59 AM
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[QUOTE=dannobee;10524979]I assume that you tried to tighten it?

No, I havenít touched it. Want to confirm what it is first and proper torque.
Old 07-15-2019, 12:06 PM
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Quote:
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Are you sure it isn't leaking from above and collecting there.
Could be, Iíll have to check it more closely after my next drive.
Old 07-15-2019, 12:07 PM
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That's the case through bolt for the intermediate shaft. The main through bolts go all the way through, but some are threaded in to the case half and then only have the one side go through. This one is threaded in to the case web on the other case half. If you've tried tightening it and it won't seal, then the only other thing I could think of is to remove the nut and clean the surface and reseal it. Wayne recommends using black silicone to seal the nut in his rebuild book. Obviously, if you go that route, you'll want to consider draining some oil. Also, removing the compression on the case web may cause issues with the case sealant between the webs. I haven't experienced this, as I'm still finishing my first rebuild, but I've read other accounts here of having the sealant crack or otherwise lose adherence to the case mating surface from loosening and then torquing nuts back down.

As for tapping the case side shown in the picture, I would say don't do that. By removing the stud and just plugging it with a bolt you are removing the clamping force on one side of the intermediate shaft and it's the outer one. So the only stud holding the intermediate shaft in place is the one in between it and the crankshaft. Sure, an M8 stud will fit through an M10 thread, but now you also have to consider that you are trying to seal a larger hole than an M8 is designed for.
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Old 07-15-2019, 12:26 PM
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Just put an aluminum washer under the nut.
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Old 07-15-2019, 02:21 PM
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Try this.......

Quote:
Originally Posted by john walker's workshop View Post
Just put an aluminum washer under the nut.


Use new nut and aluminum washer. And torque it correctly.

Tony
Old 07-15-2019, 02:31 PM
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This is a common mag case issue, requiring complete engine disassembly for a definitive fix, with band aids temporizing (sometimes successfully for a long time).

But you have an aluminum case. I wasn't aware that this stud had a tendency to pull on them. 18.4 lbs/ft is the torque spec, same as the case perimeter bolts.

What JW says is about all you can do for the moment. I used (on a mag case) a seal called a Doughty (?sp) seal, which is a rubber O ring crimped to the middle of an aluminum washer. Can't say it completely plugged the leak, but certainly cut down on it. Some sealant on both sides of the aluminum part wouldn't hurt.

I suggest you do this, and see if it will take the spec torque. You can feel a stud (or bolt) if it starts pulling. You could just put a wrench on it and tighten some, but probably better to improve the barriers to leaking first - overtightening has led to problems here and there when we succumb to the obvious temptation.
Old 07-15-2019, 02:43 PM
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And be sure that if the case is ever apart that the tapped hole is fitted with a Timesert or Casesaver before reassembly. I did tap and insert a bolt on my old 2.7 and it worked fine until we had the motor rebuilt.
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Old 07-16-2019, 01:00 PM
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Quote:
Originally Posted by walt View Post
Are you sure it isn't leaking from above and collecting there.
step one.

then -maybe- split the case...
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Old 07-17-2019, 03:57 AM
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You need a dowty seal. Rubber bonded to the inside of a washer, like the example below. They come in a wide assortment of sizes. If the surface is not damaged, and the oil is migrating down the stud, guaranteed to work.

https://www.ebay.com/itm/180-Pcs-Metric-Dowty-Bonded-Seal-Oil-Washer-Assortment-Kit-10-SIZE-M6-to-M24/233287918921?hash=item36510b2549
Old 07-17-2019, 06:05 AM
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Suggest using Permatex 574 or equivalent to help stem the flow along with the Dowty seal. However, the area should be clean and dry when applying. Not sure if this can be accomplished at the bottom of the oil sump.

Sherwood
Old 07-17-2019, 10:27 AM
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Wow guys, thank you for all the replies and suggestions. Itís not leaking a lot but itís enough to bug me. Hopefully I donít have to tear this engine down for many years. PO completely rebuilt it 8000 miles ago and it runs really well.

Itís a Ď79 with aluminum case. I doubt itís pulled. My main concern was taking tension off the bolt. Sounds like itís not an issue to loosen replace washer and re-torque.
Old 07-17-2019, 11:43 AM
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To add to the list of possible solutions, try adding Dow111 (silicone grease) or equiv. to the area under the washer. It's a heavy-bodied non-petroleum lube and might help seal that area from leaking gravity-pressurized oil.

BTW, a product called "Super Lube" (tubs and caulking tubes) is available (try big box DIY stores). Many desirable lube qualities. Much cheaper than the 3 or 5 oz tube sold by DOW (111) and others.

Sherwood

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Old 07-17-2019, 12:33 PM
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Dowty seal washer

Heres a pic of an original dowty washer, they came standard in the all the lower end case gasket kits back in the day for all 911 engines up to 2.7
I dont recall them in the later case sets, this will definitely help stop any leaks from that stud. they are readily available online
I use the dowty washer first, then a standard aluminum washer on top of that, then the nut
Old 07-17-2019, 12:36 PM
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