Engine Mount Bolts Anti-Seize Warning

Indi

Indi

Member
I have managed to strip the threads of all three holes in the aluminum bracket that bolts to the engine mount, which I think is because I used anti-seize.

I torqued it to the spec in the manual (60Nm + 90degs), the torque wrench is only a few months old and came with calibration certification.
I reused the bolts, which according to the manual should be replaced every time, but as far as I know the consensus is that they can be reused as they are 10.9 high tensile steel so should not stretch beyond the yield point in our application, with even some Audi mechanics reusing them.

The only cause I can see is that I used anti-seize on them, which reduces friction meaning for a given torque more tension is applied to the bolt. I have heard varying figures about the amount to reduce torque settings when using anti-seize, (anywhere from 10 to 30 percent) but assumed it would probably all still be within tolerance anyway so didn't bother.

1703084096718.png

The bolts labeled '2' are the ones I'm talking about.

luckily the bracket comes off quite easily so I can get it on the pillar drill to drill it out larger and use some kind of TimeSert or Helicoil type thing.
I'll also compare one of the reused bolts to a new one just to see if there is any stretch, though I suspect not.


Thought I'd mention here, might save someone else a headache 🤣

Indi
 
It is the angle that gives the final tension and the angle is the same if the bolts are clean and dry or greased. I grease all of my screws into aluminium to prevent galvanic corrosion. Can’t say I have noted any particular problems except where a female thread has fatigued through multiple retightening or where the female thread was previously subject to galvanic corrosion.
Grease increases the tension on the torque portion of the specified torque but that is a percentage increase on a small torque. Were your female threads fatigued or corrosion damaged?
 
This thread was a timely reminder for me, I have one of these castings in my scrap box and I have since bought some large coils.
One thread was stripped and the other two are damaged. I suspect I’m looking at windy gun damage from a previous owners timing belt change.
IMG_0884.jpeg

I’ll coil it tomorrow.
 
philward said:
It is the angle that gives the final tension and the angle is the same if the bolts are clean and dry or greased. I grease all of my screws into aluminium to prevent galvanic corrosion. Can’t say I have noted any particular problems except where a female thread has fatigued through multiple retightening or where the female thread was previously subject to galvanic corrosion.
Grease increases the tension on the torque portion of the specified torque but that is a percentage increase on a small torque. Were your female threads fatigued or corrosion damaged?
Click to expand...
I'd have thought one factor in torquing up a thread is friction, male thread to female thread, which any lube on the thread will greatly reduce. Is that not the case?
Mac.
 
PlasticMac said:
I'd have thought one factor in torquing up a thread is friction, male thread to female thread, which any lube on the thread will greatly reduce. Is that not the case?
Mac.
Click to expand...
Yes it will on the torque portion of the specified torque, less fiction = more tension in the fastener. However if the thread has a pitch of 1mm and you add 90 degrees the fastener elongates by 0.25 mm. the tension increase must be the same with or without grease.? I just takes less effort to turn 90 degrees with grease present.
Thinking logically grease must be good as it reduces surface to surface friction? Never thought of that before. What do others think.
 
This document suggests 25% torque reduction when using anti sieze. I'm sure other documents are available ...
Mac.
 

Attachments

  • torque_specifications.pdf
    86.2 KB · Views: 56
I can’t access the document through my phone. However a 25% reduction in torque to achieve a desired tension or compression seems reasonable.
 
philward said:
Yes it will on the torque portion of the specified torque, less fiction = more tension in the fastener. However if the thread has a pitch of 1mm and you add 90 degrees the fastener elongates by 0.25 mm. the tension increase must be the same with or without grease.? I just takes less effort to turn 90 degrees with grease present.
Thinking logically grease must be good as it reduces surface to surface friction? Never thought of that before. What do others think.
Click to expand...
If subtracting 25% of the torque setting for greased bolts is correct, (so if a greased bolt tightened to 45nm has the same tension as a dry bolt tightened to 60)

Then the difference between that bolt at 45nm vs torquing it up to 60nm as I did is probably a quarter turn or more, at which point the 60nm + 90degs I used is equivalent to 45nm + 180degs or possibly more?

So if the -25% rule is correct, and 45nm + 90 is the correct values for a greased bolt, it makes sense how 45nm + 180 would strip the threads…

I didn’t really think about it too much beforehand obviously, and it depends on how much of a rotation the jump from 45 to 60nm is I guess.

I’ll have to test it, if getting from 45 to 60nm only takes a 20 degree turn then I can’t see it making much difference, but if it’s 90 degrees or more then that’s a lot of force…
 
Torque is function of friction in the threads. So if you grease it then you are add more tension as you already figured out 😑
 
Loves a bit of grease just like @philward does! Always reused these type of bolts on hundreds of cars, never torqued but never had a problem either just gone by feel. In recent years it's been factory thread lock which seems to have caused me the most grief damaging threads upon Undoing steering rack bolts on Fiat's!
 
Are they blind holes? Years ago I was warned about greasing things into blind holes as it can create a hydraulic lock causing this kind of issue?
 
This is the warning from the manual...So do not use anti seize as contains graphite!!!!

t Tightening torques apply only to lightly greased, oiled, phosphated or black-finished nuts and bolts.
t Additional lubricant such as engine oil or gearbox oil may be used, but do not use lubricant containing graphite.
t Do not use degreased parts.
t Tolerance for tightening torques ± 15 %.
 
Wow!
The things we take for granted😳
Thanks Audifan will just use oil, going to get one of those small oil cans and have it full of oil for bolts/nuts etc. Top tip from Audifan👍
76C8E0A0-2CF3-4B2D-87B3-4161D4D6702C.png
 
Just planning my little torque experiment and gathering data.
60Nm + 90 degrees appears a bit high to me so checked the manual, that is the torque specified by Audi
Checked 7Zap, bolt is M10 * 60 and I know they are grade 10.9
Checked maximum torque for grade 10.9 M10, 75Nm for self coloured and less for zinc plated. Audi bolts are plated.
My thinking at the moment is that 60Nm + 90 is too much for a M10 into aluminium, it will strip out. I have never stripped one because like @Howey I pull up non critical bolts such as these by feel.
 
For those 3 bolts the factory torque is very close to thread failure …

In my case I have decided to change those to M12x1,5 (it can be done without removal of the lower part)
IMG_5554.jpeg


IMG_5553.jpeg
 
One of the three threads in my casting cleaned up nicely with a M10 tap. The holes are strange as the first 5mm is clearance before the thread. The other two threads are stripped to 10mm deep. To give the aluminium a chance I chose a 25mm, under the washer screw giving 20mm in the female thread. It almost pulled 60Nm before stripping. The thread was lubricated as @audifan posted.
My conclusion is the manual is wrong and the specified torque is for a M12 bolt.
IMG_0885.jpeg
 
You must log in or register to reply here.
Back
Top