Torque wrenches versus old parts

[grenjs]

I've been using torque wrenches for years to tighten every nut and bolt on basically everything. I have a choice of 3 in my garage (various makes and torque scales) and I even carry one of them in the van so that it can be used to torque up the wheel nuts should I have a puncture and have to change the wheel.

When working on our van, I clean every nut and bolt ensuring the threads are clean from grease and dirt before re-using them. In some instances I renew the bolt or nut if they show any sign of chewing, rust or stretching.

Recently I examined my engine and found one bolt loose on the engine mount and another missing altogether on the exhaust mount. In addition, I currently have a small oil leak in the oil cooler take-off/oil Filter/oil cooler/oil pipe banjo/oil bracket area. I now think it's the oil bracket itself causing the problem. However all these bits were torqued properly (the oil bracket was also sealed with a new gasket) using the torque setting recommended in the Bentley manual. The oil banjo, the oil cooler and oil cooler take-off have all been tighten beyond the recommended torque setting as otherwise they will weep oil.

Because of the loose/missing bolts and this oil leak, I thought that perhaps my torque wrenches needed calibration, but checking them against each other and they all seem to be close enough. I feel fairly confident now that if I were to tighten the oil bracket up more, the leak will stop, but it'll be over the recommended VW torque setting for it - just like the oil cooler take-off/oil Filter/oil cooler/oil pipe banjo are.

So I'm now thinking that perhaps the VW/Bentley recommended torque wrench settings are intended only for brand new parts and not for the re-assembling of old parts which may be partially worn or otherwise.

Has anyone had similar experience of torquing nut and bolts only to find them loose or missing later? Do you torque every nut and bolt when working on your van?

P.S. Yes, I do also use a locking fluid when recommended!

[kevtherev]

Has anyone had similar experience of torquing nut and bolts only to find them loose or missing later? Do you torque every nut and bolt when working on your van?

As much as possible I do yes, however, I'm sure you have also thought that the click just doesn't seem enough once torqued down.
For heads and hex bolts into alloy then it's torqued.... steel bolt on steel/nut is just done up as tight as I can

[grenjs]

As much as possible I do yes, however, I'm sure you have also thought that the click just doesn't seem enough once torqued down.

Yes indeed, when the wrench clicks, I sometimes think it's not tight enough. The sump bolts are a classic example, they appear only to be slightly tighter than 'hand-tight'.

In the case of my oil bracket (ali onto the engine block), that was cleaned, new gasket applied, sealed and torqued properly and it leaks. It was the same for the oil feed pipe going into the top. Cleaned, new washers either side of the banjo, torqued up and it leaked. Only tightening the banjo bolt up beyond the recommended torque stemmed the oil flow from it. So now the oil bracket itself is going to get tightened more, only I'm not keen of going beyond the recommended torque values - which of course prompted this post about torque wrench settings versus old parts.

[kevtherev]

As much as possible I do yes, however, I'm sure you have also thought that the click just doesn't seem enough once torqued down.

Yes indeed, when the wrench clicks, I sometimes think it's not tight enough. The sump bolts are a classic example, they appear only to be slightly tighter than 'hand-tight'.

In the case of my oil bracket (ali onto the engine block), that was cleaned, new gasket applied, sealed and torqued properly and it leaks. It was the same for the oil feed pipe going into the top. Cleaned, new washers either side of the banjo, torqued up and it leaked. Only tightening the banjo bolt up beyond the recommended torque stemmed the oil flow from it. So now the oil bracket itself is going to get tightened more, only I'm not keen of going beyond the recommended torque values - which of course prompted this post about torque wrench settings versus old parts.

banjo connections are usually quite good at sealing high pressure lines. their tight close threads offer a get out if it leaks from the recommended figure, I asked my pipe fitter friend this question and he also says that a 1/8 further turn will not be detrimental to the bolt, the torque figure is a recommended figure not a set in stone value as the DIY tool is not tested to the accuracy the value given by VW tooling.
He also says that a good washer is important, too soft and it leaks on the torque.. to hard and it leaks ..you can't win!

[grenjs]

As much as possible I do yes, however, I'm sure you have also thought that the click just doesn't seem enough once torqued down.

Yes indeed, when the wrench clicks, I sometimes think it's not tight enough. The sump bolts are a classic example, they appear only to be slightly tighter than 'hand-tight'.

In the case of my oil bracket (ali onto the engine block), that was cleaned, new gasket applied, sealed and torqued properly and it leaks. It was the same for the oil feed pipe going into the top. Cleaned, new washers either side of the banjo, torqued up and it leaked. Only tightening the banjo bolt up beyond the recommended torque stemmed the oil flow from it. So now the oil bracket itself is going to get tightened more, only I'm not keen of going beyond the recommended torque values - which of course prompted this post about torque wrench settings versus old parts.

banjo connections are usually quite good at sealing high pressure lines. their tight close threads offer a get out if it leaks from the recommended figure, I asked my pipe fitter friend this question and he also says that a 1/8 further turn will not be detrimental to the bolt, the torque figure is a recommended figure not a set in stone value as the DIY tool is not tested to the accuracy the value given by VW tooling.
He also says that a good washer is important, too soft and it leaks on the torque.. to hard and it leaks ..you can't win!

VW are my first port of call for parts and these washers were from VW - so I hope they are good. Mind you, VW have changed the material from which the washers are made - used to be a copper material, now changed to an alloy of some sort. In this instance a good 1/4 of a turn stem the flow.

I just need to find the right tightness (which will not be the VW recommended torque setting) for the oil bracket itself to stop that leaking. As you will know, the bracket is a royal pain in the a*** to get to.

[Titus A Duxass]

There is an commercial argument for using the lowest possible torque figure.
If we do not provide a torque figure and the customer shears the bolt or, more likely, strips the thread in a casing - the customer can knock on our door and demand free repair.

If we give them the highest level and they do the same - they will come to us and say that it is our problem as we set the torque level.

If we give them the lowest possible figure whilst still meeting the tech spec/requirements they are less likely to experience Maintenance Induced Damage.

[grenjs]

There is an commercial argument for using the lowest possible torque figure.
If we do not provide a torque figure and the customer shears the bolt or, more likely, strips the thread in a casing - the customer can knock on our door and demand free repair.

If we give them the highest level and they do the same - they will come to us and say that it is our problem as we set the torque level.

If we give them the lowest possible figure whilst still meeting the tech spec/requirements they are less likely to experience Maintenance Induced Damage.

Well I didn't know that, but I entirely understand the commercial argument - that's fair enough. But what you are saying is that the recommended torque settings aren't then the optimum or best torques for assembling these components, but rather a 'safe' minimum level to avoid these commercial issues arising. I surmise further that the 'safe' minimum settings were calculated by the designers for use on brand new manufactured parts being assembled together (e.g in the factory) rather that older components which inevitably in one way or another will have some 'wear and tear'?

[Titus A Duxass]

I surmise further that the 'safe' minimum settings were calculated by the designers for use on brand new manufactured parts being assembled together (e.g in the factory) rather that older components which inevitably in one way or another will have some 'wear and tear'?

Correct - we do not take wear and tear in to account.
We would rather the customer buy a new one, most of our equipment has a service life of 12 - 15 years but does not get stripped down very often (the reliability is quite high).

[grenjs]

I surmise further that the 'safe' minimum settings were calculated by the designers for use on brand new manufactured parts being assembled together (e.g in the factory) rather that older components which inevitably in one way or another will have some 'wear and tear'?

Correct - we do not take wear and tear in to account.
We would rather the customer buy a new one, most of our equipment has a service life of 12 - 15 years but does not get stripped down very often (the reliability is quite high).

I certainly don't question the reliability. Some of the vans have clocked up some incredible amount of mileage. But when things do need repairing and there isn't a need for a new part - say dismantle, clean-up and re-assemble, then I suggest the recommended torque wrench setting should then only be used as a general guideline and the actual amount of torque should be more than if new parts were used - maybe (finger in the air guess) up to 15-20% more. So instead of 20Nm the bolts, nuts or whatever should be tightened maybe to 24nm.

I'd be interested to know what that percentage figure is!

[kevtherev]

Two grunt%

[dash]

Torque tightening bolts is an incredibly imprecise business.

[jamesc76]

the only thing I use a torque wrench on is head bolts and wheel nuts of motors! Ok the Trains I work on are a different thing all together, But im a mechanic by trade and do things up to what I deam them to need all by hand, but with time you can feel when a bolts close to shearing or stripping threads

[colinthefox]

Going right back to your initial post, it seems that the oil bracket is leaking. If this is where it meets the engine block, it's probably nothing to do with how tight the bolts are. The casting warps, and doesn't sit flat on the block. What I do is to lap the face of the aluminium bracket on a piece of abrasive on a sheet of float glass till it's flat, then refit and not tighten too much. They all leak if you just re-fit them.

[grenjs]

Going right back to your initial post, it seems that the oil bracket is leaking. If this is where it meets the engine block, it's probably nothing to do with how tight the bolts are. The casting warps, and doesn't sit flat on the block. What I do is to lap the face of the aluminium bracket on a piece of abrasive on a sheet of float glass till it's flat, then refit and not tighten too much. They all leak if you just re-fit them.

Thank for the info. Will try that tomorrow.