Sooo...How do you guys feel about Loctite? My understanding is that it does not effect torque values.

Can I assume that if no angle value is given, torque is pretty much what you have to work with?

A whole bunch of misses on the "replace with stainless" direction. The choice of fasteners wasn't made by accident by Porsche. (even though there is room for improvement...)

A Porsche can be expected to last for years and part of that comes from the material selection the engineers used.

- Stainless fasteners mixed with steel fasteners: Not good
- Stainless fasteners in aluminum: BAD
- Stainless fasteners in magnesium: REALLY BAD

The choice of what dissimilar metals are allowed to be used with each other is really important. The reason has a number of names: Anodic Index or Galvanic Index which all comes under the heading of Galvanic Corrosion

The cathode (more noble) will "eat" the anode (least noble). In the case of stainless with aluminum or magnesium that means the fasteners will eat away at what they are fastened to.

As a rule of thumb you want to keep the different metals within 0.15V of each other if at all possible. If the fastener is more anodic then the metal it is attracted to that is good because it protects the metal of your parts. If you look at the anodic index you will see that steel is very close to aluminum which is good and you will see that zinc galvanizing is very anodic which protects the parts. All of this is done for a good engineering reason.

If you are worried about exhaust components corroding look at copper plated fasteners instead of stainless. It may seem counter intuitive with copper's placement on the anodic index but it isn't in contact with the actual engine parts. Plus copper is very, very resistant to heat and when used as a plating on a steel nut with a steel fastener you end up with a very seize resistant combination.

This is awesome, thanks. Those are surprisingly big variances and a nice bump for the angle technique.

If you don't have the copper-plated stuff handy, even adding a bronze washer would be an improvement. I have a small cache of copper-plated fasteners and it seems I have to keep reminding knuckleheads to stop plundering it for other uses.

I did swap to stainless from the low-grade non-metric aftermarket fasteners on my 987 exhaust hangers. However, if you look to where it matters, the car has stainless secondaries fastened with copper-plated nuts and bronze washers. It's possible that these may even be Porsche parts; the stock nuts are priced at a $1 each, so it seems unlikely that they are zinc-plated steel.

More evidence, perhaps, that Porsche engineers do know what they are doing? ;)

Outside of Porsche, I'm frequently surprised by what I find and there are many more cases where an upgrade (usually in steel grade) seems appropriate. Maybe there are just a lot of people out there using Home Depot hardware?

+1 for Carroll Smith's books
 

It is rare to find an accomplished, articulate and occasionally humerous man like Carroll Smith.

A little tongue in cheek comment that would have driven him over the edge:

"Cross threading is almost as good as lock tight".

or, "If a hammer won't fix it, the problem is probably electrical".

I just sent my son a copy of Prepare and Tune to Win - and am interested in his "education", (he has a WRX :-(

chris

FWIW... The differential bolts in my SC failed. I had an experienced Porsche dealership mechanic look at them and he said they were probably torqued wet.

The results... This is one of the better ones. You can just see the crack at the base of the threads.

http://forums.pelicanparts.com/uploa...1424493037.jpg

So I would torque them dry unless otherwise stated.

Carroll Smith would probably reuse that bolt, if it passed his "flotation test". Simply throw it in the ocean. If it floats, it's safe to put back on the car. :D

Loctite does and will always affect torque to preload relationships - there is nothing you can do to a thread which will not have some effect.

Many articles about Loctite claim it has no effect but IMHO you should decrease the specified dry torque values by around 20% when using the Loctite Purple, Blue, Red or Green thread lockers. We carried out trials many years ago when looking at the bolting of high speed flexible couplings used on helicopter engine test rigs.

The corrosion issue is interesting particularly with regard to Magnesium.

We are using a thread primer on all of the head studs we use in magnesium engines.

Many aftermarket studs are a stainless steel or similar material that is more difficult to threadlock than conventional steels.

We have been making a 170 ksi Titanium Stud for these engines and the corrosion index is even less favourable than stainless steel and needs to be dealt with.

The primer has two effects - it is an activator that forms a bond with the stud lock and it electrically isolates the stud from the thread.

Cost of fasteners in a production environment is also a major concern.

In most reference I've seen specifying general torque, for example 24 Nm for an M8 8.8 grade, it has called for clean, untreated and lightly oiled threads.