A little history:

A Logical Discussion:

Topic: Rocker/valve cover retaining nut torque for Porsche 911s built between 1965 and 1989.
Rocker covers evolved through four generations; (1) aluminum upper and lower (6-nut type) used from 1965-67, (2) magnesium upper and lower (11-nut type) used well into the ‘70s, (3) aluminum upper and lower (11-nut type) used on most ‘77s, early Turbo Carreras and early SCs, and (4) aluminum upper covers with heavily reinforced lower aluminum covers often called Turbo covers.

Gaskets also evolved; originally made of cork, then graphite composition, then a version with a silicon bead (lower) as well as ultra-thin, firm, self-sealing gaskets that ranged in color from green to almost blue. Hardware, always 8mm, stayed the same with one exception – very early 2.0 911s were frequently seen with non-locking upper cover nuts used in combination with wavy-type lock washers.

That’s the history. It is fact that the early cork gaskets could squeeze out from between the early covers and cam housings, especially under a heavy hand tightening the nuts. As a side note, my shop used cork gaskets (lowers were available for both 6-nut and 11-nut covers) to help seal up leaks caused by warped magnesium covers. Those covers were never “torqued,” just tightened by feel and using the visible gasket edge as an aid.

Along came lean burn engines, thermal reactors and excessive heat, which, in a way, was responsible for the development of the superior gaskets that we have today.
All the while, a plate (used through about mid-’83) on the bottom of the engine, usually referred to as an oil screen cover or a sump plate, saw fewer gasket changes; from thin paper to graphite, then to an improved even thinner graphite. No change to the torque spec for its 6mm (quantity 8) nuts was made – that held at 10Nm (7 lb/ft). Think about that for a moment; tiny 6mm nuts, each used with a wavy lock washer, tightened to 7 lb/ft.

Back to a set of rocker covers, sealed with graphite upper and lower gaskets. Those gaskets were quite firm, and about 1/3 the thickness of cork versions, it made sense that more torque could be applied. Certainly the hardware was up to the task, after all, it was identical to the crankcase perimeter hardware and the chain case to crank case hardware – 8mm Nylok nuts and aluminum sealing washers. Specified torque for that hardware? 25Nm (18 lb/ft).

The period through which gasket technology changed was interesting for my shop. Many of my customers bought new cars, and some opted to have us perform the required 1,000 mile service, rather than have it done at the dealer by an unknown (yes, Porsche approved this and all warranties remained intact). We noticed, while doing those jobs, how tight the factory-installed rocker cover nuts were, and realized it was due to the new gaskets, and eventually better lower covers. We re-checked the Spec books (by this time we were servicing SCs), and decided that the “All bolts (fasteners) on crankcase and camshaft housing, M8 = 25Nm” had to take precedence over the note about a “cover, M8 = 8Nm” which co-incidentally appeared in the torque spec list with the camshaft bolt/nut spec.

So, we used 18 lb/ft on a large number of cars, new and old with the latest gaskets, discovered that disassembly at the next scheduled service was perfectly normal, and made that spec routine for all except the cars that used cork gaskets.

We have now reached the point where the latest version sump gasket became identical to the chain case, crank case gasket. To review, the torque for the 6mm sump plate nuts is 10Nm, the torque for the 8mm chain case nuts is 25 Nm. The rocker cover gaskets that have been available for many years are thin, firm, and self-sealing. Rocker cover hardware is 8mm. Why would one consider 6 lb/ft – ONE LESS than the considerably smaller 6mm sump plate nuts, reasonable and appropriate for that 8mm hardware?

One must conclude that the 6 lb/ft spec; (1) was a typo (M8 instead of M6) that turned into a monster, (2) was a correct spec, but for original rocker covers using cork gaskets, or (3) was that it referred to the [3] 6mm bolts that secured the “cover” at the end of the camshaft inside the chain case, and two mistakes were made – one a typo and one in translation.
My personal belief is that #3 above is correct because; (1) the reference to a “cover” with “M8” hardware appears with the torque spec for the bolt/nut on the camshaft, and (2) that “cover” is called a “chain case cover” in later Porsche repair manuals, is noted to have, and is secured with 6mm hardware, and recommended torque is 8-10Nm (6-7 lb/ft).

FYI: Later factory technical spec lists do a far more thorough job elsewhere as well. Not only did they finally correctly define “cover,” they itemize the specs for M8 hardware on the crankcase, M8 hardware on the cam housings, M8 hardware on the chain case, and included a spec not seen before – “Valve cover to camshaft housing.”

I can't speak to after market gaskets, I've only used factory approved gaskets throughout my career.


For follow-up: http://forums.pelicanparts.com/porsche-911-technical-forum/507325-what-torque-911-valve-covers.html?highlight=valve+cover+nut+torque

Exactly Peter!!!! Guys if you follow Peter's instructions,you will never have a leaky valve cover,unless you didn't get the surfaces clean.
Howard

Thank you Peter for this. Years of experience and hands on with the evolution of our cars speaks volumes. I asked a question and received my answer and hopefully others will now have a reference. You are a value to us all.

I used the gaskets and hardware in a kit sold by our host. Thick might not have been an accurate description I just used it as compared to the few other gaskets I replaced. My sump plate was next and your paragraph on that was a bonus.

I did a lot of wrenching on VW Diesels and ran 2 of them to 500k each and another to nearly 300k. I only torqued my wheels and head bolts nothing else and never had an issue. Just limited in the aircooled and soft metal motor make up knowledge and experience. Sometimes the searches seem so specific as to our cars that maybe too much knowledge can be dangerous (to our mental comfort).

Thanks to you guys there are really very few mysteries to our cars.

Terry

BTW I snugged them all up even to my feel than tried my 3/8 torque wrench which started at 10 ft/# and clicked at 12.

"FYI: Later factory technical spec lists do a far more thorough job elsewhere as well. Not only did they finally correctly define “cover,” they itemize the specs for M8 hardware on the crankcase, M8 hardware on the cam housings, M8 hardware on the chain case, and included a spec not seen before – “Valve cover to camshaft housing.”

Peter,..what years are you speaking of as to "later factory technical specs"? (post SC)... What were those specs?

I recall reading this post from Zimmy long ago,..it was well rx'd,..very informative,..thanks.

Best!

Opened up my valves cover last week, one silicon gasket was torn at two corners (no leak). I am not sure if tight nuts did this, but I torqued them at 6 lb/ft. I am doing 5 lb/ft now. Let's see how 5 lb/ft torque on the next valves adjustment.

You'll not go wrong listening to JW, but when I was starting out, and overly concerned about leaks, I wanted to do it to spec so I picked up a torque wrench from a bicycle shop (a Park) that's in inch/lbs for a reasonable price. 72 in/lbs is what I set mine at. Didn't read the rest of this thread...also make sure you tighten them in the proper pattern...at least that what I do. Pete Zimmerman has also posted extensively about what value to set them at (much higher than 6 lb/in) as I recall, so it's obviously NOT something that has to be exact...

edited: I REALLY should read the whole thread before I post :)....sorry 'bout that Pete (et al)

ps: mine get torqued to 6 (the orange/red silicon gaskets) and have never leaked a drop....YMMV

I just snug them down by hand, never had a leak, never had one back off.

Just to possibly clear it up the 964/993 VC studs are 6mm and along with rubber gaskets only require 72-84 inch lbs (6-7ft lbs). Perhaps he was given this spec. For cars with turbo exhaust VCs, Upper covers, with thicker gray/graphite gaskets 15.5 ft lbs, Lower Turbo VCs 18ft lbs with thin green, or green w/white silicone bead gaskets.(Wrightwood racing)
If your running early exhaust VC's or magnesium covers with gray graphite lowers than 15.5ft lbs on the lowers also.
But remember this is for 8mm studs.

Hmm, may try a lesser torque than the "oil field method" I've done in the past.

I just can't justify a torque wrench on a non-critical fastener.....

The problem with 6ft pounds is is often isnt .. It takes about 3-4 ft pounds just to get passed the nylock resistance.

Same here - in 30+ years I have never used a torque wrench on small sized fasteners such as these and have never had a problem with over or under tightening.

New, but related topic, hopefully not as exhausting:

How much torque should I apply to the radio ON/OFF knob? :)

S

Only one problem with that; all mechanics are not created equally. Everyone's forearm "clicks" at a different point, and if you spent 40 + years loosening fasteners tightened by people that didn't use torque wrenches, like I have, well...

Believe me, I'm not talking about you, but the average technician cannot "feel" 6 lb/ft, or 18 lb/ft, or 65 lb/ft. I can, but I still use a torque wrench because I also know that on some days I'm stronger than on other days. 16 lb/ft on one day can be 19 lb/ft the next day. My torque wrenches protect me from that.

The same amount that the lug nuts on my E350 call for - 145 ft. lbs. (and I use a torque wrench on those - ha!)! :D

Good point - it is definitely difficult to judge torque with little to no experience.

Thanks. Do you think I need an adapter for my 1/2" drive impact gun?

S

Not sure about that, but if the 1/2" drive impact doesn't work, try a 3' breaker bar. :p