copper slip on torqued bolts

[wemorgan]

Confession time.

On my brake pad slider pin I put some copper slip on the shaft to allow the pad to slide freely, but then without thinking also put some on the thread. I've no idea why, I never usually do. So when I came to torque the pin the torque wrench never met the required setting, the pin continued to screw in and when I stopped to look why it was taking so long I saw a crack in the aluminium caliper. Stupid mistake. Thankfully a second-hand replacement is only £40. But nevertheless, lesson learnt once again, don't put copper slip or grease on threads that are going to be torqued!

 

[Dieselman]

Or accept the reduced torque required.

You should be able to feel the thread tightening to locked.

 

[Godfrey]

Perhaps why cylinder head bolts are similarily usually put in clean but dry too.

 

[moonloops]

Hydraulics lesson 101

 

[Godfrey]

Hydraulics lesson 101

Are you reckoning that the copper slip was pushed into the void and the pressure burst the alloy? (rather than the threads by being lubed not being able to attain the required torque before fatiguing - which I had assumed)

 

[wemorgan]

(rather than the threads by being lubed not being able to attain the required torque before fatiguing - which I had assumed)

That was my conclusion too.

The slider pin was only threaded at the head, so the excess copper slip was free to be pushed through the caliper housing. My theory was that friction between the threads was too low to meet the required torque.

 

[st13phil]

Perhaps why cylinder head bolts are similarily usually put in clean but dry too.

Some cylinder head, big end and main bearing cap bolts are lubricated with oil before torquing up. That's why you should always check rather than assume...

 

[markjay]

In the olden days I used to coat every bolt with a touch of copper grease, saves lots of problems later on.

However it is true that current advice is not to do this on torqued bolts, for the reasons stated, including roadwheel bolts and spark plugs which should be tightened to torque with dry threads.

Said that, my 2001 Vauxhall came at the time with factory-fitted Bosch spark plugs covered with generous amount of copper grease... go figure...

 

[jamesfuller]

This is one of those topics that not every one will ever agree on. A clean and lightly lubricated thread will ensure the correct torque is attained, as apposed to dry corroded threads that may bind and give a false torque reading.

There are of course times this doesn't apply, If the manufacturer of a component/fastener says install dry, its quite often something with some form of thread lock added by them. The manufacturers testing and research is carried out on new fasteners and sometimes into what they consider reasonable life expectancy!

 

[Chrishazle]

The steel casing and tubing we ran into the various oil and gas wells I worked on came with a variety of threads and thread lubricants, each size/thread had a recommended make-up torque and each lubricant had a "torque factor" to be applied to the recommended make-up torque. This factor was 1 for "API Standard Pipe Dope" to as low as 0.7 for some more specialised thread lubricants., particularly those used with threads that had a metal to metal seal on the nose of the male thread. A couple of decades back Shell (?Nigeria) learnt the lesson the hard way by wrecking a lot of VAM thread (expensive, metal to metal seal) production tubing by making it up to recommended torque and not applying the correction factor!

I would hazard a guess that the torque correction factor for copperslip would be in the 0.7-0.8 range.

 

[m1br]

Many head bolts are tightened by angles for this reason.... so are oil filters

 

[markjay]

I would say that a tiny spot of grease at the tip of the bolt will spread thinly on tightening and will not affect the torque settings significantly for most applications, other than where the torque has to be very accurately set e.g. head bolts.

On another note... should you re-torque bolts that were originally tightened with Locktite applied?

Or do you remove them, clean, re-apply Locktite and then tighten to torque...?

 

[NOMONEYBUTAMERC]

When I checked out the torque settings on some bearing housings , for a customer , I was advised by SKF that standard practice is to state all torque settings for dry components. The technical guy said they had a number of instances where people had caused damage by applying the same torque to components which had been greased.

 

[mejermy]

I wonder how precise most car torque wrenches are. I understand that, with the exception of , e.g. aviation tools, unless they are calibrated regularly they can easily be 10-20% out.

 

[wemorgan]

My Sealey (7-112Nm) torque wrench when new came with a calibration certificate. I forget the exact values, but I think it showed it to be 1-2% accurate over the whole range. It is 3 years old now, so it could be worse. ps. I wind off all the torque when storing.

 

[markjay]

For most applications torque accuracy is not actually that important anyway, as long as all bolts are tightemed equally (e.g. cam cover or oil pan).

The reason behind this is to do with the principles behind 'tolerance'.

Tolerance applies only to mesaurments, but not to settings. So when measuring a gap, the tolerance might be say 0.15 to 0.30 mil, but when tightening a bolt there will be only one figure.

This makes it very difficult to asses whem a certain torque setting is given as a precise figure, or it just a mean figure within an acceptable range.

In the olden days, only head bolts were torque tightened (using angle torque wrench), anything else was done by 'feel'.

This worked fine for experienced mechanics, but had limited scalability.

The main reason behind the wide spread use of torque settings these days is to allow shorter training periods for assembly line workers and service technicians, and obviously to allow greater uniformity of the final result (e.g. you don't have to use a 'good" mechanic to achieve a good result...)

 

[regbuser]

When AMG technicians assemble one's lump, do you think they use feel or digital feedback torque drivers?

 

[Dieselman]

When AMG technicians assemble one's lump, do you think they use feel or digital feedback torque drivers?

Neither. They use powered drivers with preset torque ratings.

Don't forget, these engines are not lovingly put together by a "craftsman", but whacked together on an assembly line by a semi-skilled factory worker called Florian Brader.

He hasn't got time to muck about reading torque wrenches, you know.
http://www.mbclub.co.uk/forums/engine/132722-amg-engine-builder-mystery.html

 

[jamesfuller]

When AMG technicians assemble one's lump, do you think they use feel or digital feedback torque drivers?

An air gun set to 3 dagadagadagas (the technical term is FT)

 

[markjay]

I am willing to bet that if Olly was to work on cars personally for one week without a torque wrench (not including head bolts), you'll find that all the bolts and nuts are torqued within the error margin of the torque wrench...