When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I was using an impact driver with an impact allen head (with no extension shaft). As well as undoing direction, I also gave the bolts a bit of doing-up direction. All to no avail, and I got to the point where I had stripped one of the threads.
I then tried to weld a nut onto the allen head, but my arc welding was not good, and I never got a strong weld – the nut just came away.
So I then took the wheel hub off, positioned the half shaft ready to be moved out away from the side of the car, lowered the exhaust somewhat and cut the remaining 3 bolt heads off.
I was then able to remove the half shaft, leaving the bolt shafts behind.
Which I was then able to remove with my finger-tips!
My conclusion (but very happy to be told otherwise) is that the bolts were just being held in by tension from being tightened hard.
A couple of days back I ordered some bog-standard stainless steel M10 half threaded allen-headed bolts that I was going to put on instead of using the Porsche part 900 067 123 01 – as I was thinking that stainless steel would minimise corrosion etc, but now I am wondering if the softer steel in the Porsche bolts is used for a reason (e.g. it is stretchy) and I should buy the proper parts instead.
I am somewhat surprised that the fasteners came off that easy given I half expected you would find the stubs seized to the half shaft flange but there you go- it is history- now forget it.
Stainless steel has some advantages but it also has some disadvantages. As I am aware SS common grades cannot be hardened due to the low carbon content whereas the stock bolts will invariably be grade are 12.9 items [as per WSM] and those are classed as high strength fasteners. Stainless does not fare well corrosion wise when exposed to rock salt [sodium chloride] as in what is used to prevent roads icing up in the UK. Stainless also tends to work harden and thus not so good in cyclical stress services where it may have a tendency to fatigue.
Stock 12.9 Allen bolts must be readily available in the UK so why take a risk? As I recall I put some copper slip on the bolt shaft [not the threads] when refitting my half shafts.
Last edited by FredR; 01-31-2023 at 11:36 AM.
Reason: Corrected the bolting material grade
If stock is 12.9 or 10.9 then you must find similar ones as these are higher tensile bolts. Normal is 8.8. You may find 12.9 stainless alloy bolts but these are rare. The other important thing is corrosion. The stainless bolts will eat away from the steel plates = will loosen with corrosion and time.. Go with the original bolts and specifications..
I'm a big fan of replacing with stainless where I can, but never for bolts that see real stress. I'm sure I'm using the wrong term, but my impression of the stainless bolts is that they are more brittle (is that the opposite of tensile strength?), and thus less able to withstand the stresses which they might see in something like holding an axle shaft.
@FredR makes a suggestion that I am totally on board with: anti seize will help you avoid issues in the future, though, hopefully, this issue is handled for a long time!
Ian, the three machine-screws that came out: How did they look? Was there any corrosion? Along the unthreaded shaft, or just at the threads?
Some photos of those fasteners that came out may show some clues.
Certainly, if the car sat for a couple of decades, anything could happen-- moisture getting to the bottom fasteners but not the top ones, who knows...
Your previous thread indicated no movement at all. That suggests corrosion along the length of the fastener, not just corroded threads. If it were only the threads that are locked, then the shaft would twist a bit-- experienced fingers would feel that. But not at the far end of long socket extensions-- those twist also. (Which is why impact wrenches are much more effective when close to the fastener).
One thing I like to do with stuck fasteners is to go back and forth-- if it doesn't want to loosen then try a tug in the opposite direction-- back and forth. If there is any movement at all, that will help the anti-seize to wick in. That's a real limitation of extractors-- internal or external-- they only loosen. A welded nut-- or even vice-grip pliers if you can get them in there-- will go both ways.
The best anti-seize is a mix and acetone and ATF by the way. Kroil (kroil.com) is also very good but may not be available in the UK. I don't know how Seafoam compares. Heat may also help break up the corrosion, as mentioned.
Cheers,
Good advice, and the acetone/ATF mixture is usually given as 50/50. Works very well.
I'm a big fan of replacing with stainless where I can, but never for bolts that see real stress. I'm sure I'm using the wrong term, but my impression of the stainless bolts is that they are more brittle (is that the opposite of tensile strength?), and thus less able to withstand the stresses which they might see in something like holding an axle shaft.
@FredR makes a suggestion that I am totally on board with: anti seize will help you avoid issues in the future, though, hopefully, this issue is handled for a long time!
Cheers
G,
Tensile strength is an absolute measure- the ultimate tensile strength [UTS] is the stress at which the material "let's go". The yield stress [YS] is the stress level at which the material will permanenty deform and thus will never return elastically to the point it was originally. Metals typically used in engineering have a characteristic such that in round terms the ratio of UTS to YS is around 1.5. Brittle materials typically demonstrate a lower ratio whereas as ductile materials can exhibit a higher ratio. As I recall stainless steel [SS] is not particularly brittle but it is vulnerable to work hardening when exposed to cyclical stresses it can and does fatigue- have you ever seen a cylinder head bolt made of stainless steel? I doubt you ever will.
Engineers typically work to design codes and those in turn define what percentage of yield stress can be used in design- rarely will this ever exceed 90% of yield but there are exceptions. For example some cylinder head bolt designs are specified as "torque to yield" but not the 928 head bolts which is why "in theory" they can be reused. However if you have followed the discussions on cylinder head corrosion it is clear that as part of the corrosion process hydrogen is liberated and bolts exposed to such can be subjected to hydrogen embrittlement- this in turn can generally be reversed but unfortunately if such bolts are undone before the condition is reversed it will invariably induce micro cracking and render the bolts useless for further use. In the oil industry we typically limit design to 60% of yield on process plants with the additional 30% considered as a "safety factor" margin.
The 12.9 number in the bolt spec is a measure of the bolts UTS for design purposes and whereas it may be possible to achieve such values with some grades of stainless why bother when the correct item is readily available? Buy them from Porsche and they will doubtless cost more but they for sure will be the correct bolts- a bolt supplier will supply the same thing cheaper assuming they are a quality outfit but then the question is confidence in their supply chain.
As a veteran of the 'second guessing the factory on halfshaft fastening' war, I've gotta tell you....Don't go there! Those puppies do a lot of damage when they come down whilst in motion.
Tensile strength is an absolute measure- the ultimate tensile strength [UTS] is the stress at which the material "let's go". The yield stress [YS] is the stress level at which the material will permanenty deform and thus will never return elastically to the point it was originally. Metals typically used in engineering have a characteristic such that in round terms the ratio of UTS to YS is around 1.5. Brittle materials typically demonstrate a lower ratio whereas as ductile materials can exhibit a higher ratio. As I recall stainless steel [SS] is not particularly brittle but it is vulnerable to work hardening when exposed to cyclical stresses it can and does fatigue- have you ever seen a cylinder head bolt made of stainless steel? I doubt you ever will.
Good comment and info overall. But stainless headbolts are not that rare. Especially in pwc's, like jetskis and two-stroke engines they are quite common...
01-31-2023, 06:32 AM
