What happens to greasea as it ages?

[Calvin Sambrook]

Having spent a "fun" weekend totally stripping down and rebuilding my 20 year old touring bike because the bottom bracket seized... and then I noticed the wheel axels were stiff... and then I noticed the headset was tight... I was wondering why grease turns into something resembling glue after a couple of decades. The bearings were all sitting in quite "tacky" grease about the consistency of impact adhesive.

The grease I was using to re-lube was Castrol LM, a lithium grease, which comes in a tub with a cover over the grease with a hole in the middle. You push the cover down to get some grease up through the hole. I had always assumed that was simply to keep the unused grease clean but I saw that the older smears around the top part of the tub (it's at least a decade old!) looked very similar to the stuff on my bike, no longer flexible and very tacky whereas the product under the cover was fine so I guess it's something to do with reacting to air.

Anyone know what's going on?

[Andy Champ]

At a guess - the volatile components have evaporated.

Andy

[Bob Minchin]

Quite normal behaviour. Grease is oil & soap. The latter dries out. Old grease is normally driven out under pressure by fresh grease from a grease gun but for something like a bike, it should be stripped down every few years.

Bob

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Calvin Sambrook" saying something like:

Grease is just an oil with a filler, and the oil contains volatiles.

[Matty F]

Grease in a torque wrench may harden and cause the readings to be vastly wrong, causing bolts to be overtightened and threads to be damaged. Which fact seems to have been omitted in this report of an aircraft windscreen that fell out:

your torque wrench at least every year, or preferably every time you use it!

[Cicero]

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The hole is there to facilitate the filling of grease guns; remove the end of the grease gun and press the body down over the hole in the tin. The protective plate moves down in the tin and grease flows in a 1" stream into the grease gun.

Cic.

[Andrew Gabriel]

I use Finish Line for regreasing my bicycle bearings. It's never gone hard as you describe. It gets dirty after a while, and as it's deliberately white so any dirt shows up, that's clear to see, at which point I wash out the old grease before reapplying.

I thought it was specifically a bicycle grease, but on checking the tub, it doesn't actually say that anywhere on it. It says it's a 100% synthetic grease, loaded with micron sized teflon balls, with a film strength of 200,000 PSI (which should just about handle my pedal force;-) and an operating temperature of -65F to +500F. Never carbonises under heat or pressure, never separates out, and keeps bearing surfaces dry even when operating fully submerged.

I bought it about 10 years ago in a specialist cycling shop, and the 16oz tub is going to easily see me out. Cost £13.

Having now read that, I might try it for some other things too.

[dennis]

wrench would do any thing bad in this case. AIUI a broken torque wrench might have stripped the smaller bolts and the whole thing would have been avoided.

I have no doubt that they do test the torque wrenches.

[PeterC]

At a guess, the oil evaporates from the soap. I bought quite a lot of Campag. Record hubs and pedals in the '80s and always stripped and rebuilt them as the Campag. grease was like cold lard. Some of the MTB greases are quite good - more gel-based.

[PeterC]

Thickened grease can be quickly and temporarily thinned by movement and some WD40 (sorry).

[BigGirlsBlouse]

Grease is a soap containing the lubricant in suspension... the lubricant dries out leaving just the soap

[Derek Geldard]

Thence to collect dust and turn into proto-stone.

Derek

[Matty F]

I believe that the "mechanic" managed to strip the threads, which then caused the window to fall out as soon as there was any pressure on it. It was discovered that many other planes had the wrong size bolts also but those had not failed.

They had not tested that torque wrench for five years. It was discovered that the grease in that type of wrench was unsuitable and a different grease was recommended. But nobody bothered to notify all the users of the wrenches.

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[John]

The idea behind the cover with the hole was to assist in filling a grease gun. You pressed the gun cylinder down and the grease was extruded up into the gun. (can't help on the ageing. I have a tin (plastic with a crack) which seems okay after about 30 years (It is a moly grease)

[Dave]

The effect of the grease was mentioned, but it looks like it was not detrimental to the torque loading. What was done wrong was the over torque loading of the bolts on the assumption that at re torque after

100 flying hours, they would find a quantity that had managed to unscrew themselves.

What did strike me about this, was the manager didn't spot the different bolts by either the weight, feel, or use of the fingers to run over the screwed in bolt's countersunk head. That alone should have alerted him to the fact that the bolts were the wrong ones. Countersunk fasteners must comply with quite strict tolerances regarding their levelness to the aircraft structure.

The use of bolts of the correct diameter, but 0.1 inch shorter would not make all that much difference from the right length. One thing I noticed that was missing from the report was a visual check of the bolt tail protrusion out of the anchor nuts. I presume that they were hidden behind cockpit trim and that the illustrated parts catalogue should have been consulted for the correct length, diameter and part number to be used.

that came to light in the military side of aircraft. The RAF have a very robust system in place in the 700's books.

Now there is a problem here, what do you cross check a torque loader against? We have no calibrated tools to check them with.

Dave

[Matty F]

I gathered that the bolts were tightened to double the correct torque because of the hardened grease in the torque wrench, but perhaps I remember it wrong.

The heads of the incorrect bolts were smaller than those of the correct bolts. That made it easy to find the incorrect bolts on many other planes without having to unscrew them. The manager should have noticed the head size.

I would check it against a simple spring gauge. Not better than 10% accurate but a lot better than 100% wrong as was the wrench that was used.

[dennis]

AIUI it stated that you couldn't tell the difference between the thread slipping on the smaller bolt and the torque wrench operating.

The report did state that the torque wrench made no difference to the accident.

[Dave]

You have a chicken and egg situation here. How do you check the accuracy of the spring balance? I suppose you could calibrate it with an empty paint can and fill it up with a measured amount of water though.

When I worked in the industry, my boss asked me to test some ones own torque wrench on our calibrated measuring machine that we used to set a particular torque wrench up with. The wrench was one of those that had an adjustable rotating handle, so that you could set any torque within its range and the wrench would 'break' near the end when the torque was reached. Despite its age, it was remarkably accurate.

Dave

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Matty F saying something like:

I would suggest against a known weight sliding to set points on a bar.

[Calvin Sambrook]

Thanks everyone for broadening my understanding of this. I know I should have re-lubed my bike at some point over the last two decades but it's just one of those jobs I never got around to (long list ! ).

Despite having an "O" level (sort of like a good GCSE for any youths here) in Chemistry I was in fact that kid mucking about at the back of the class so I now have to admit to not really knowing what soap is made from and how (hangs head in shame). Anyone care to tell me?