"Correct" torque value for valve cover nutsrs for

[KFC911]

I'm attempting to clarify what "may" be a common error. I've always used 6 ft/lbs (using a torque wrench) as the "correct" torque value for tightening the valve cover nuts (I "sneak up" on that value by tightening them to 4, and then going back over to 6 in a criss-cross pattern from the middle > out) and have never had a leak from the valve covers. Recently, Pete Z. (a "real pro" who I have utmost respect for) stated that his shop always used 18 ft/lbs, and that 6 is "incorrect".
The Bentley manual (Carreras), and both of Wayne's books (Rebuilding 911 Engines and 101 Projects) and everything I've read until recently also state this value, so I'm just seeking clarification so "I" don't continue to pass along bogus information. I've checked the factory manuals and could not find clarification. Here are a couple of recent threads:

Do I need an inch lb torque wrench?

http://forums.rennlist.com/rennforums/showthread.php?t=436940

http://forums.rennlist.com/rennforums/showthread.php?t=398876&page=7&highlight=valve+adjustment

According to Pete, the "6 ft/lbs" is an error from an early Porsche spec book that has been propagated forward and is just "flat wrong". Many times, experts can disagree (and I'm certainly a novice when it comes to 911s) so I'm just seeking clarification. I realize many simply go by "feel", and there are often times several ways to achieve success, so that's the purpose of this post. What do you guys use: 6 ft/lbs, 18 ft/lbs, "an experienced hand", or "other" for the valve cover nuts? I'd particularly like to hear from some of you veterans who've performed countless valve adjustments and who I always depend upon to keep folks like myself (a weekend garage "hack") on the correct path. I'd like to thank everyone in advance, and want to make it clear that I'm not "arguing with Pete", as he has been a tremendous asset in my "quest for knowledge" over on Rennlist for some time. I also want to make it clear that this thread is for my "own" edification, so if you would prefer to send me a PM (instead of posting here), that would be fine, but I suspect that many are in the same "boat" that I am however, so I would welcome a discussion. Thank you all!

[burgermeister]

I use something like 6, but I have silicone gaskets ... but it's more of a "torque to contact, then add another 180 degrees of rotation" kind of thing.

If they drip, I snug them up a bit more.

[livi]

Keith, my man! Are we straying from OT into unknown tech wilderness??

Me?? As we all know, I am an utmost tech newbie. But with a bit of beginners luck I have so far done six valve adjustments (not all on my car, mind you!) on old 911s. All by 'inexperienced hand feel'. So far everybody is happy.

[pope]

I'm another one of the newbies. I've done two on mine both at 8Nm (about 6ftlbs). Started with 5Nm crisscrossing inwards and then retorqued to 8Nm in the same pattern. Silicone gaskets. Covers are dry as a bone now.

[KFC911]

Originally Posted by livi

Keith, my man! Are we straying from OT into unknown tech wilderness?? ...

Markus, I have strayed away from the land of the loonies, and as Steve Winwood would sing "...and I can't find my way home"...HELP ME ! I too use the silicone gaskets and have never had a leak so I've always passed along the 6 ft/lbs information when other newbies ask...that's the primary reason for this post (as I feel like I should stop if it is indeed incorrect). 6 ft/lbs absolutely works for me, and "if it ain't broke, "fix" it until it is". Or something like that...

[rllevin]

The little white Porsche Technical Specifications book for the the 911 Carrera, 911Turbo calls for 8 Nm for the "cover to camshaft housing m8." Whether this is the rocker cover or chain cover I don't know.

[Rot 911]

I alwasy followed what Warren (Early S Man) said and never had a problem or a leak:

"The specific torque value, and Lee is right, of 72 in-lb, or 6 lb-ft ... was not specified until the 'late' factory graphited gaskets with the incorporated green bead of silicone rubber came out around 1981. And that 6 lb-ft rating was first published in the '78 thru
'81 SC Spec Book, dated 31 March 1981.

Up until that time, no torque value at all was specified in the spec books, and everyone just assumed 'hand-tight' wasn't going to rxceed the 'normal' M8 torque value of 18 lb-ft. And, of course ... the original cork gaskets tended to crack or squeeze out in all the wrong places!

If you look at a normal 'combination' wrench of the 10 mm size ... it is no longer than the width of your palm, so, if you do the opposite of 'choking up' on a baseball bat, that is ... snug your four fingers right up next to the box-end of a 13 mm combination wrench, and tighten the valve cover nuts with the wrench held that way, you won't over-torque the nuts, and you don't have to worry about buying a 1/4" drive torque wrench to measure 72 in-lb of torque! Why did I pick an 10 mm wrench? Because a normal DIN 8.8 M6 fastener uses a 7 lb-ft torque specification, that's why!"

[Peter Zimmermann]

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.”

Logic.

[livi]

Thanks Pete! Great post!

Welcome to Pelican! Giving up on Rennlist or just completing the picture? I always read your posts over there. Very informative and nice. Thanks for coming here, contributing with your wealth of knowledge!

[pope]

Sounds perfectly logical Pete. But my gaskets had been squeezed by the PO to the point of showing outside the covers. I remember thinking that they hadn't been tightened THAT much and yet the gasket was squished and they were leaking.

Of course they were magnesium back then and I replaced them with Turbos.

I'd be cautious in tightening them more. Maybe next time I'll step it up a notch, go big and tighten them to 15Nm or something

[Rot 911]

If 6 ft. lbs. works, and based on no one complaining about leaks or nuts backing off, at that torque setting, why torque to 18 ft. lbs.?

[KFC911]

Thank you too Pete! For those of you who don't visit Rennlist, I think it's pretty evident and Pete's post speaks for itself...the man is an absolute wealth of knowledge and has been gratiously assisting "us hacks" over there for some time now. I think I too will stick with what's been working well "for me", but I will discontinue my practice of telling other newbies to "do as I do" and simply direct them to this thread instead

[KTL]

I'm a lemming and have been torquing mine to something around ~100 in. lbs. = 8 ft. lb. They don't leak so I never considered making them tighter.

Periodically i'll check the nuts and find they can be tighted/snugged a bit more after the new nuts and gaskets have heat cycled a number of times. So obviously the 18 ft. lb. value is reasonable. Plus that's the standard spec. for most any M8 fastener that is 8.8 property class. The only downside I can see to using 18 ft. lb. is that it doesn't allow you to reuse the standard gaskets as easily! That sound you hear is Pete puking at the thought of that.......

[Peter Zimmermann]

Originally Posted by KTL

The only downside I can see to using 18 ft. lb. is that it doesn't allow you to reuse the standard gaskets as easily! That sound you hear is Pete puking at the thought of that.......

LOL!!! Markus, Keith, Kevin and others with nice words - thank you. Please also consider that my perspective is from the shop owner/mechanic side; there are just some things we had to figure out how to avoid. The primary issue was customer inconvenience, we just couldn't expect a client to come by the shop (with 22 million people in L.A. traffic is a bit of a problem!) to re-check nuts because they weren't tight enough in the first place. Valve adjustments had to last 15K miles, which meant that the covers had to remain drip free for an extended period while driving in the harshest conditions - heavy traffic and high temperatures. Everything my shop did was geared toward simplifying our customer's driving experience, and it was very satisfying to see an SC or 3.2 car come in for its 15K mile service, and have bone dry valve covers that were also easy to remove and clean. Oh, the gaskets...no, re-using them was never an option ! We preferred the super-thin greenish/blueish version because; (1) they were easy to remove (most often in brittle pieces), (2) cleaning was super easy (gaskets with the silicone bead left crud behind that often required razor blade work), and (3) with flat covers and clean cam housings, they just didn't leak.

To you DIYers out there, I salute you - it's another adventure. Please remember, what you do to your car is your biz, and how you do it won't affect anyone other than you. Mine is just one voice, one opinion, and should you choose to follow my suggestions know that they come from experience gained in the trenches, working at a professional level. We used to have a saying in the shop: "There is the right way, the wrong way, and the Porsche way." We worked hard to stay somewhere between right and Porsche, and everything that I write will hopefully reflect that.