928 Tech Tips

many questiosn are asked around the bolt size of tyhe oil pan. There are two different sizes:

25 M6x28
5 M6x25

The short ones go at the thinner spots around the pan.

Theo

http://928gts.jenniskens.eu

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Been warned continually to not over tighten the oil pan bolts. Couldn't find a torque specifically mentioned in the fiche manual, only a general ref to 6 mm bolts to be torqued to "4.3+1.7" ft-lbs. or a total of 5.7 ft lbs. Well, I don't know if that is the right torque to apply. I have a nice little torque wrench that goes to 100 Inch-lbs. Twelve make a ft-lb. So I guess I will use it to torque to 55 inch-lbs and be done width, UNLESS SOMEONE TELLS ME OTHERWISE.
--jer
83S A/T
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Jerry,
The torque for a Grade 8.8 M6 x 1.5 should be about 6.64 ft-lb/79.66 in-lb (9 N*m), Grade 10.9 = 9.59 ft-lb/115.06 in-lb (13 N*m), Grade 12.9 = 10.33 ft-lb/123.91 in-lb (14 N*m), all specs for iron bolts and lubricated threads. The most common reason folks over torque the oil pan bolts is their tendency to back out. Rather than use a thread locker that might result in twisting a head off next time the gasket needs to be changed, I use locking bolts. In case you're not familiar with these, they have a small nylon (or Teflon, which is best for this application due the heat) ball near the end of the bolt that helps prevent it from backing out .... They are available at some hardware store, or places like McMaster-Carr, Grainger, etc.

Ray

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RC,
They are probably the 8.8 kilogram per millimeter strength bolts (roughly equivalent to our SAE grade 5). BUT, in this particular instance, these bolts should not be tightened that tight. I went to 60 inch-lbs ...well, actually I was going to go to 60 inch-lbs and my magic wrist told me that this was too tight for this application. Bolts have a certain feel -- it's hard to describe -- but I just know that for the oil pan smashing that thick gasket, 5.7 ft-lbs is just too much. So I am settling for 40 inch-lbs which equates to about 3.3 ft-lbs.

Now let us wait to see what Wally, Jim, Marc, Mark, Mark, Walt, Dan, Tony, Frank, Fred, Burt, Wendle, (and if I missed anyone who should be on this list, please accept my apology) say I should use as the actual recommended oil pan torque.

I was pleased to find in my tool box a cute little 10 mm box-end kludge wrench I had welded up to a 3/8" square socket to make kind of a crow-foot with closed end wrench. I made it years ago and have no idea what for. But it is sure nice for a lot of those pan bolts around the sides near the front. I will have to suitably adjust the torque reading to account for the offset of the center of the shaft from the center of the bolt, but Ah kin do it!

And as far as thread locker goes, if you use grade A (red) Loctite, you may very will twist off a bolt that has a long run of threads into a casting. It is better to use the grade C, (blue) which will retain the bolts, but will come loose. There was also a purple Loctite called "Screw Lock" which has a lower breakaway torque, but they may not make that stuff any more. (I think I will got to the Loctite website and see what the latest info is on their stuff) I also have some green Loctite stuff called "Retaining Compound" which you put on stuff that you NEVER NEVER EVER want to come loose.
--jer
83S A/T

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Actually Jerry,
There are no specific specs for the oil pan bolts (at least not in my set of manuals), just a generic for the size .... 6+2 N*m (4.43 ft-lb+1.48 ft-lb=5.91 ft-lb/70.81 in-lb), but if you want to pick nits over 0.79 ft-lb (8.85 in-lb), be my guest. I've been using 9 N*m (6.64 ft-lb) with the Tef-lock bolts since the first time I replaced the OP gasket, and never had one snap, nor do I have the usual leaky oil pan. Yep, I'm familiar with all the various Loctite products (as well as countless adhesives, epoxies, solvents, etc), but I prefer the Ny-lock or Tef-lock bolts and locking nuts (when applicable) .... cleaner installs, no need to clean up the threaded holes when removing/replacing bolts .... Personal preference, of course.

I also have quite a bit of experience with the "feel" thang that encompasses everything from cutting tools, to whether or not a drummer is just enough behind the beat to get a blues tune "in the groove" ....
;)

Regards,
Ray

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Beware,

The generic torques that are offered in the manual pertain to NON-gasketed joints. These are general torques right out of the metric fastener handbook. when you put a few millimeters of cork between the surfaces that becomes the limiting variable not the yield strength of the fastener. When a company like Porsche designs a gasketed joint you have to rely on them to tell you how to tighten it but they rely on their factory training program for that because it isn't called out very clearly in the books.

Torque of the pan needs to be low and even. You can actually feel the gasket seat and begin to squish. As you go around the gasket you can feel the torque of the fasteners become even. The gasket is not a precise synthetic material so the torque is somewhat random. Clean new fasteners always helps. But torqueing to the standard 55% yield number will limit the life of the gasket and worse may warp the soft aluminum pan flange.

A few foot pounds is probably near too much but close.

jfk

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When I installed my silicon OPG about 2 years ago, I used the "Erkka" method for tightening it: tighten all nuts exactly till the point that the underlying washer can not spin anymore, hence test many times when tightening (in my case M6 nu-locks nuts were used). Then turn all nuts 2/3 of a turn. There you have it: equal pressure everywhere.

Has been perfect ever since.
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Arnoud

1994 928 GTS PK