What is the correct torque for the connecting rod nuts on a 1970 914-6 (aka 1969 911T)?

* The factory manual says: 5 mkp (49 Nm, 36 ft. Lbs.)
* Wayne Dempsey’s book says: 20 Nm (14.7 ft. Lbs) +90 degrees
* Bruce Anderson’s books says: 37 to 40.5 ft-lb
* There was a Porsche Technical Service Bulletin in 1990 (for some models starting with MY 1978) saying bolts marked “12.9”: 15 Nm (10.5ft lbs), +90 degrees, +90 degrees). They reference part number 964–103-176-00

The part number I bought for new rod bolts was 901-103-172-00 for 1970 914-6 (same as 1965-69 911). They are marked 12.9.

So I have an early MY, with different part number, but marked 12.9. What’s the correct torque?

Merry Christmas

I would not use 12.9 ft/lbs or anything +90 degrees

Around 35 - 40 seems like the right number

Check with Jeff Hines.

Reminds me of the Oscar winning performance by Marissa Tomei. Merry Christmas and best wishes with your project!

Nobody can answer that question. It's a trick question.

https://m.youtube.com/watch?v=XZ-UHY6HXdU&a...xdWVzdGlvbiA%3D

https://m.youtube.com/watch?v=y8hcfTFVJ9k&a...2N1cmF0ZQ%3D%3D

Why do you not believe the factory manual or the Bruce Anderson reference to be reliable information?

I am sure they were both accurate at the time of release. The technical service bulletin and rod bolts marked "12.9" came well after that, so it gave me pause.

I had to make a call to keep moving, so earlier today I went with 36 ft lbs. For better or worse.

I think you made the right call.

The tech bulletin references a different rod bolt part number and later model engines. So not really relevant to early engine rebuilds. Likewise, the bulletin doesn’t make any mention of that change being applied to the part numbers for earlier rod bolts.

The OEM tests extensively to determine proper torque spec for the application. Regardless of how bolts are marked, you’re buying a OEM bolt via OEM part number that meets OEM spec. Specialty bolts like a rod bolt have no requirement for standardized marking so as far as we know 12.9 marking on them could refer to anything (revision level, supplier ID, etc.).

Wouldn’t surprise me at all if later engines torque and angle spec were changed for manufacturing reasons in addition to the material change mentioned. DC nut runners used in manufacturing have much less process variation when used with torque and angle control rather than torque only.

https://www.atlascopco.com/en-us/itba/exper...orque-and-angle

In the end, either method is going to target a fastener that is at about 75% of yield after tightening, and a resulting clamp load that will keep the parts fastened together under design intent loads.

wow,, hope you figured it out.. 00 weird porsche mistake in rod bolts

I would be going with the guys that designed and built the motor , seem to remember from Pelican there were rod bolt issues with later bigger motors hence the change and need to put out a service bulletin .
Haynes manual states 36 ft/lbs and that info comes from the factory.
If Dennis is using bolts correct to the rods there won't be any issues as long as the rods have been measured and checked correctly.
.

Change in technology guys...

Earlier stuff was always a final torque number.

When they changed to "stretch to torque" style fasteners you commonly see an initial low torque value then an angle change or a series of angle changes.

I believe (with the proper NEW fasteners) the angle method is better overall but there is "not a snowballs chance in hell" I'd install modern technology hardware into an engine that was NOT designed specifically for them.

Old 911 stuff should stay old 911 stuff unless you are making massive changed to the engine. Stock should stay stock.

Almost everything new that directly bolts into the engine block has an angle torque value and (if you read the service manual) is supposed to be replaced after a single use.
Head bolts/rod bolts/front crank bolt, flywheel bolts, main/rod bolts, intake, exhaust are common to be replaced at service.

I've always wondered if this method was implemented more for reduction in production cost than for actual "improvement of the breed".
I'm guessing it is easier for an automated machine to come up to a low torque and then make an angle-based tightening change than to accurately turn a bolt to a specific torque.

I might be wrong...

SuperHawk?

Truth be told, I REPLACE modern new style fasteners with old style quite often.

Stretch bolts get changed to nut and stud with final torque numbers.

Every performance engine I build will at least have aftermarket head studs.

ARP is my normal go to brand.

I cannot remember intentionally changing TO stretch to torque EVER!

Forgot to mention NEW GERMAN stuff that could be SUPER important.

BMW changed to blocks that had a much higher content of magnesium in the early 2000's
The blocks are visibly grayer than the cylinder heads.

Every single fastener that bolts into the block is made out of aluminum, inverted torx heads (most of the time) and have a blue dot inked on the top.

There is a sticker in the engine compartment that states "fasteners marked with a blue dot are single use and should be replaced if removed" or something similar.

OH MY GOD! are they serious!

The bolts are CHEAP and always available at the dealer...

I tried to re-use a starter hold down bolt on my mom's 07 X3. I got the starter aftermarket and the BMW dealer is 50+ miles away.

I'm good at this shit.
I know how to re-use single use fasteners.
I was being CAREFUL, super soft torque application.
AS I reached what I believe was MINIMUM torque the bolt fractured about 1/2 down the shaft clean ass in two!

The BMW "blue dot" bull shit should ALWAYS be replaced, every single time...

I was trying to avoid pulling torque to yield (TTY) into this discussion because TTY is often accomplished as a torque + angle spec. However torque + angle doesn’t necessarily mean a fastener is TTY.

Confusing eh?

Based on the tech bulletin and the noted rod bolt material change, it looks to me that Porsche switched to TTY along with their note not to reuse fasteners. Side note; I’ve never been one to reuse rod bolts anyway since they are so critical. Likewise, I think DennisV’s decision to replace them with new OEM bolts is a good call!

There are a number of reasons for an OEM to use TTY ranging from enhanced durability, to cost and weight reduction. On a modern car almost everything in the design process is biased to fuel economy and emissions and money will be spent totally save fractions of a pound here and there. These small but easy weight reductions are needed to offset the ever increasing vehicle weights that result from impact standards that add massive amounts of weight to modern cars.

TTY typically allows for a smaller fastener, or using the same size fastener to achieve higher clamp loads. TTY fasteners are much better at maintaining higher clamp load in cyclic fatigue applications (like rods and cylinder heads).

So if the design can use fewer, smaller fasteners AND achieve better durability, less cost, and a weight reduction (benefiting fuel economy - emissions), it’s a no brainer. This is why you see TTY fasteners proliferating. Ease of service and the need to replace one use, TTY fastener's IF service is needed is way down on the priority list.

I agree with everything you said for the most part. Those are the reasons that are always given regarding the change to the new TTY fasteners.

You ARE plagiarizing others! I'm gonna fry you on social media!
(It WOULD help if I had a social media account, I don't.)

I've repair everyday cars and I've had more trouble with the new fasteners than the old...

Replacing TTY head bolts with studs is always seen as an improvement (or maybe we just think it is).

These studs, which are the same thread pitch and diameter (close), normally equal or exceed the original clamp force (most have larger diameter flat washers).


I think the driving force between the change was for a fiscal reason alone.

"These new engine assemble robots will replace 150 employees and over a 10-year period will save us XX.XX million dollars"...

I have yet to see an angle torque listed where they don't also say "replace fastener".

You're right! You can have angle torque without TTY fasteners but that is SO rare that I automatically see a TTY procedure as "replace fastener" as well. I could be wrong, I'd rather make an error of addition, that costs a bit more, than have a critical fastener fail inside an engine.

I reuse TTY fasteners far more often than I would like...
The service manual says replace so I call the dealer; not in stock and 5 days to get...
Shit!
Next questions is "have you ever sold any, especially through your shop?"
If the answer is "no" then I'll probably re-use.
If the answer is "hundreds" I'll bitch and say "Why the hell don't you keep that in stock? you useless parts critter!"
Note: I am friends with most of the parts guys/gals local to me.