What’s this nut that’s leaking oil on my engine?

[Derek77]

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.

[dannobee]

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.

[walt]

Are you sure it isn't leaking from above and collecting there.

[Derek77]

[QUOTE=dannobee;10524979]I assume that you tried to tighten it?

No, I haven’t touched it. Want to confirm what it is first and proper torque.

[Derek77]

Originally Posted by walt

Are you sure it isn't leaking from above and collecting there.

Could be, I’ll have to check it more closely after my next drive.

[jons911]

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.

[john walker's workshop]

Just put an aluminum washer under the nut.

[boyt911sc]

Originally Posted by john walker's workshop

Just put an aluminum washer under the nut.

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

Tony

[Walt Fricke]

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.

[Jack Stands]

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.

[Flojo]

Originally Posted by walt

Are you sure it isn't leaking from above and collecting there.

step one.

then -maybe- split the case...

[onevoice]

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

[911pcars]

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

[Derek77]

Wow guys, thank you for all the replies and suggestions. It’s not leaking a lot but it’s enough to bug me. Hopefully I don’t have to tear this engine down for many years. PO completely rebuilt it 8000 miles ago and it runs really well.

It’s a ‘79 with aluminum case. I doubt it’s pulled. My main concern was taking tension off the bolt. Sounds like it’s not an issue to loosen replace washer and re-torque.

[911pcars]

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

https://en.wikipedia.org/wiki/Polytetrafluoroethylene

[porschyard]

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

[g3ngs]

Found this thread after experiencing a weep from the same through bolt.

First attempt to fix was by double nutting the through bolt back in as far as it would go, which wasn't very far as you don't have many threads to play with on the bolt as it comes out of the left side of the case, then adding silicone grease, a dowty washer and then another washer on top before putting a new nut on.

Worked great (just as long as you don't drive the car)... Took it on a 200 mile round trip to an event and the faintest of weeps came back.

Here's what I've done now.

• Removed the through bolt and found it to be 125mm long
• Of this 15mm is threaded to left and shows though the case on the left to take a nut and washer
• 110mm of the through bolt is inside the two halves of the case
• On removing the through bolt 8 pulled threads were observed.

• I then measured the full depth of the whole (with a rod thin enough to fit)
• The full depth of the hole from the face of the case on the left is 120mm

• I then cut some steel zinc plated M8 stud to 140mm
• This was double nutted in 120mm until I felt it biting and giving resistance and carried on until it would go no further
• This left 20mm showing out of the left of the case

• The face of the case where the stud came through had silicone grease, on top of that was a M8 dowty washer, a normal washer and nylock nut
• A ratcheting 13mm spanner was used to nip the nylock tight
• Torque wrench set to spec 25nM (crossed fingers) then tightened it until it clicked

My assumption based on this is that the whole depth of the hole in the right side of the case is threaded and the 10mm that has bitten to 8 threads (10mm / 1.25mm thread pitch)

If the whole of hole depth in the right side of the case was not threaded I would have cut 2 or 3 flutes with a dremel to 3 threads depth so as to chase / tap into the empty recess of the through bolt into the magnesium of the case.

[AG81]

^
Nice.....

This was but one of my leaks on a 20yo 4800 mile completely rebuilt motor all done under previous ownership. I opted for dropping the motor and completely disassembling and checking everything.

[EC900]

I remember reading this back when it was posted. Had the same issue. I was lucky, all it needed was to be re-torqued.

[Mike Czech]

I had this issue on my '77 911S mag case as well. I found a good YOUTUBE video which suggested backing out the bolt with two nuts, applying sealant on the threads, and then re-threading the bolt into the case with the two nuts. It worked for me. No more leak.