JasonAndreas

Does anyone know what the torque specifications are for the four 10mm nuts that attach the engine carrier 964-115-021-90 (suspension) to the engine studs?

springer3

If that is a 10 mm nut, I believe the stud would be 6 mm diameter, or M6. I don't know the factory recommendation, but "Fastener Facts" torque table for a Property Class 8.8 M6 nut is 95 in-lb (8 ft-lb) dry, and 57.5 in-lb (4.8 ft-lb) lubricated. Property Class 8.8 is the same material as the SAE Grade 5 (heat treated) fasteners. The torque value for Property Class 10.9 (like SAE Grade 8) is 132 in-lb dry, and 79 in-lb lubricated. Please verify the stud diameter is 6 mm before using any torque spec.

If I did not know what the Property Class was, I would put thread paste on the threads ,and torque to the lubricated Class 8.8 value. The studs and nuts may be Class 10.9, but the stud is in the aluminum case. I am surprised there is not a hardened flat washer between the nut and the metal plate. Did the factory leave it our, or are your's just missing? A hardened washer considerably improves performance of this type of bolted connection.

Edit - first post had "ft-lb" where units were "in-lb"

garrett376

If you don't mind educating me... how does the washer do this? And what is the performance improvement? Thanks Springer!

springer3

Sorry, I have been playing with bolt failures a lot at work lately, and perhaps am getting too technical.

A hardened flat washer is needed any time a heat-treated (hard) bolt or nut is used to clamp a non-heat-treated (soft) steel part. A hardened washer spreads the load to prevent indentation of the softer steel by the hard nut. The washer itself must be hardened so that it does not indent. Any indentation will cause the clamping force to decrease.

If the clamping force gets too low, two bad things can happen:

1) Vibration causes the nut to back off. A properly tightened nut will, by design, resist vibration.

2) The parts get loose enough to slide. For a number of reasons, threads should not be loaded in shear. They can break under shear loads. If the stud stays tight (and is designed properly), the shear load is taken by friction between the parts, and all the stud needs to do is apply clamping force.

Bolts are so simple even a young child can understand how they work. Bolts were in widespread use before engineers and scientists studied them enough to understand them properly. You have to know a lot about elastic theory and friction theory to understand what is going on. Bolts are not particularly forgiving. The best way to avoid a mistake is to trust the factory design and follow the maintenance instructions.

JasonAndreas

I should know better than to post at 6am, the nuts and studs are M10.

The nut is a property Class 10.9 yellow zinc coated nut.

There is an M10 aluminum spring washer directly behind the nut. I'm almost 100% positive that my engine carrier had never been removed before so its looks like the factory used loctite 270 on the nut.


Too technical, no such thing. Never apologize for making a post that actually explains something; there is a decent size audience here that eats this stuff up. I wish more message posts explained why you need to do something not just, "do it".

I've decided to replace every fastener thats come off my car with a new one so I've spent way too much time over the past couple of months learning about fastener specs so that I would make sure I buy the correct nut, etc. I was amazed at how inexpensive it is to buy all new fasteners the only problem being the minimum order requirements that most businesses have and the sheer number of different types of fasteners that I had no idea existed. In 99% of the cases it is still cheaper to buy a box of 100 than it is to buy 5 from a Porsche dealership. I just wish that Porsche would have provided a listing of every fastener, DIN spec and torque specification used on the car like they did for older 911s.

springer3

Jason:

M10, property class 10.9 torque spec is 53 ft-lb dry, and 32 ft-lb lubricated. If you use Loctite, I suggest going with a lower torque just to make sure you don't pull the stud or crush the washer. The lubricated torque for an M10 Class 8.8 nut is 23 ft-lb. That shoud be plenty tight, but not risk damaging anything else.

I know replacing fasteners is a budget buster. Why are you not reusing the less critical ones?

JasonAndreas

THANKS!!!!

I had to take the engine out to replace a clutch, etc. and with 10 years of crap building up everywhere I got really **** and just decided to clean & polish everything I could get my hands on. (half my car has found its way from the garage to my basement this summer, yes I need help...) Anyway, after spending way too much time cleaning I just couldn't stand to put on a corroded fastener. When I found out I could buy 100 class 8 all-metal yellow zinc coated locking nuts for around $3USD I went overboard and started ordering other fasteners.

bhensarl

You guys are my heroes. I'll never know half as much about the mundane bolts on my car as you guys do. You both are truly paradigms of Porsche ownership. Thank you.

Brian