LBS and Torque Wrench

[Colin Grigson]

There is also a difference between ‘wet’ torque values and ‘dry’ torque values. If any given bolt is lubricated prior to having a particular torque applied, it will be considerably tighter than the same bolt torqued ‘dry’. Most torque values assume ‘dry’ torque loading.

 

[DaveReading]

As mentioned somewhere above, the correct torque for a seatpost clamp bolt is just enough to stop it slipping in use. That'll be rather less than the maximum, unless you have the wrong diameter post.

"Never put a thread up dry", I can still hear my grandfather saying from 40 years ago.

 

[SkipdiverJohn]

Even on the car I've only ever bothered for cylinder heads. Rightly or wrongly I reckon I kind of know what's about right whether that's camera screws or car bits. I would bother for cylinder heads, or for things that need doing up bloody tight

I can remember removing and refitting the cylinder head on an old petrol Land Rover of mine a few years ago. My torque wrench wasn't in the same location as the car, so I just used a breaker bar both to remove and refit. To compound the felony I also re-used the head gasket!
If I took seriously some of the nonsense I've heard about using torque wrenches and never re-using gaskets, and must use gasket sealants otherwise you'll always get leaks, then the outcome should have been disaster. It wasn't. When I got a chance to, I did check the head bolts with a torque wrench and found I had got them consistently about 10% too tight, which on 1/2" UNF bolts in a cast iron engine block I am not going to lose any sleep over. The engine subsequently covered quite a few thousand 100% reliable miles with no water leaks or loss of compression.
Some stuff is more important than others with torque, it depends on the materials involved and how big your margin for error is. Honestly, some people really are a bunch of drama queens when it comes to touching anything mechanical.

 

[monkers]

Retired engineer here.

Some myths I've seen here need busting.

Torque settings quoted are optimals for the system requirements. Correct assembly procedures, observance of conditions such as with or without lubrication, sealant, or locking compound can be critical. Ditto tightening sequences and number of torque driving stages. The need to limit or control torque at point of fix can be for a number of considerations, though typically more likely a combination than any one factor in isolation.
1 Prevent stripping of thread of screw, bolt, nut, or component.
2 Prevent rounding off of head (external drive) or rounding out of head (internal drive).
3 Prevent any discernible degree of distortion to components during assembly.
4 Achieve the correct degree of 'nip' or 'crush' during assembly that is required to maintain the stability of the joint.
5 Achieve superficial (meaning across entire surface area, rather than 'trivial') spread of joint medium such as a gasket.
6 Ensure joint stability across a range of operating temperatures.

Torque settings also often play a role in the pre-loading of components, where bearing load, shaft end-float, and gear mesh are important considerations.

The criteria used to determine the recommended torque setting will include all of the above, the resistance of the structure to distortion during assembly and operation, sealing requirements, materials used, the CSA (cross-sectional area) of the screw fixings, and the form and pitch of the threads.

In many modern applications, 'stretch bolts' are used. These are single use only - they may not be re-used. Stretch bolts are not usually brought to full tightness by use of a torque wrench, but an angle gauge. The full tightening sequence for a cylinder head for a modern engine is tpically a number of critical steps, including an initial low torque setting, tightening through an angle in a prescribed sequence, tightening through a further angle in sequence , running the unit to operating temperature, allowing to cool to a prescribed temperature, loosening the fixing by a prescribed angle in sequence, tightening through a prescribed angle in sequence. A test procedure may follow, such as pressure testing of the cooling system etc.

One common amateur error is hydraulic locking. This occurs most usually where vertical blind threaded holes are present. Either the blind hole has become filled with spilt liquids during disassembly, or threads have been over-enthusiastically lubricated with oil or grease during assembly. The spilt liquid or lubrication is impelled to the bottom of the blind hole by gravity or the action of the screw and cause the screw to bottom before the desired jointing load is achieved.

Failing to remove surface oxidation before fixing is another problem.

Stretch bolts can be identified by having a waist (a bit like a double butted spoke). The narrow waist of the bolt becomes stretched during assembly - it pre-loads the joint in such a way as to help to maintain joint stability over a range of operating temperature.

A work colleague of mine bought a Mini Metro when they first came out. They had something called an 'A+' series engine. We were standing right by it after he arrived for work one morning when there was a loud 'bang'. A cylinder head bolt had 'let go' and made a clean hole through the bonnet. That became a common problem and the design was modified.

Steel bolts are as prone to becoming stripped as easily as soft alloy bolts. This is because the idea that steel is steel is steel is incorrect. All steels are alloys and their mechanical properties vary very widely. Some steel bolts are quite soft, others are really hard. Some bolts carry identifying marks, which if you happen to know them, tell you how to use them correctly. Engineers are trained to spot them.

You can assess the hardness of a steel bolt but cutting it with a hacksaw, or stroking it with a file, after which of course it is useless.

Here's a useful tip though, if you drop a BMS or LC steel bolt (bright mild steel or low carbon content) onto a hard concrete floor, the sound will be a dull thud. An HT (high tensile) bolt will sound with a brighter ring.

Older designs like the Land Rover engine mentioned by another poster somewhere upthread, will be heavy of construction, use cast iron as their principal material. The cylinder block will be low in distortion during assembly. The price of this over-engineering is an engine with a low efficiency as in low power to mass ratio. Great engines, will be readily tolerant of a deal of abuse, but of their time, and no longer valid for continuing production.

Anyway, hope this helps, and now to bed.

 

[weareHKR]

I guess the proof in the pudding will be if the seat drops at all.

Well.... after all that Torque Talk... how's the seat holding up?

 

[rogerzilla]

Retired engineer here.

Some myths I've seen here need busting.

Torque settings quoted are optimals for the system requirements. Correct assembly procedures, observance of conditions such as with or without lubrication, sealant, or locking compound can be critical. Ditto tightening sequences and number of torque driving stages. The need to limit or control torque at point of fix can be for a number of considerations, though typically more likely a combination than any one factor in isolation.
1 Prevent stripping of thread of screw, bolt, nut, or component.
2 Prevent rounding off of head (external drive) or rounding out of head (internal drive).
3 Prevent any discernible degree of distortion to components during assembly.
4 Achieve the correct degree of 'nip' or 'crush' during assembly that is required to maintain the stability of the joint.
5 Achieve superficial (meaning across entire surface area, rather than 'trivial') spread of joint medium such as a gasket.
6 Ensure joint stability across a range of operating temperatures.

Torque settings also often play a role in the pre-loading of components, where bearing load, shaft end-float, and gear mesh are important considerations.

The criteria used to determine the recommended torque setting will include all of the above, the resistance of the structure to distortion during assembly and operation, sealing requirements, materials used, the CSA (cross-sectional area) of the screw fixings, and the form and pitch of the threads.

In many modern applications, 'stretch bolts' are used. These are single use only - they may not be re-used. Stretch bolts are not usually brought to full tightness by use of a torque wrench, but an angle gauge. The full tightening sequence for a cylinder head for a modern engine is tpically a number of critical steps, including an initial low torque setting, tightening through an angle in a prescribed sequence, tightening through a further angle in sequence , running the unit to operating temperature, allowing to cool to a prescribed temperature, loosening the fixing by a prescribed angle in sequence, tightening through a prescribed angle in sequence. A test procedure may follow, such as pressure testing of the cooling system etc.

One common amateur error is hydraulic locking. This occurs most usually where vertical blind threaded holes are present. Either the blind hole has become filled with spilt liquids during disassembly, or threads have been over-enthusiastically lubricated with oil or grease during assembly. The spilt liquid or lubrication is impelled to the bottom of the blind hole by gravity or the action of the screw and cause the screw to bottom before the desired jointing load is achieved.

Failing to remove surface oxidation before fixing is another problem.

Stretch bolts can be identified by having a waist (a bit like a double butted spoke). The narrow waist of the bolt becomes stretched during assembly - it pre-loads the joint in such a way as to help to maintain joint stability over a range of operating temperature.

A work colleague of mine bought a Mini Metro when they first came out. They had something called an 'A+' series engine. We were standing right by it after he arrived for work one morning when there was a loud 'bang'. A cylinder head bolt had 'let go' and made a clean hole through the bonnet. That became a common problem and the design was modified.

Steel bolts are as prone to becoming stripped as easily as soft alloy bolts. This is because the idea that steel is steel is steel is incorrect. All steels are alloys and their mechanical properties vary very widely. Some steel bolts are quite soft, others are really hard. Some bolts carry identifying marks, which if you happen to know them, tell you how to use them correctly. Engineers are trained to spot them.

You can assess the hardness of a steel bolt but cutting it with a hacksaw, or stroking it with a file, after which of course it is useless.

Here's a useful tip though, if you drop a BMS or LC steel bolt (bright mild steel or low carbon content) onto a hard concrete floor, the sound will be a dull thud. An HT (high tensile) bolt will sound with a brighter ring.

Older designs like the Land Rover engine mentioned by another poster somewhere upthread, will be heavy of construction, use cast iron as their principal material. The cylinder block will be low in distortion during assembly. The price of this over-engineering is an engine with a low efficiency as in low power to mass ratio. Great engines, will be readily tolerant of a deal of abuse, but of their time, and no longer valid for continuing production.

Anyway, hope this helps, and now to bed.

Is that cut and pasted? Most of it is irrelevant to bikes.

 

[monkers]

Is that cut and pasted? Most of it is irrelevant to bikes.

No. I sat and typed every word. The more off topic parts were busting myths I'd read in the thread. I worked on it because I intended it to be helpful.

 

[SkipdiverJohn]

One common amateur error is hydraulic locking. This occurs most usually where vertical blind threaded holes are present . Either the blind hole has become filled with spilt liquids during disassembly, or threads have been over-enthusiastically lubricated with oil or grease during assembly.

I make a point of poking a bit of rag stretched over the end of a screwdriver into blind holes to ensure they are not full of liquid.

Here's a useful tip though, if you drop a BMS or LC steel bolt (bright mild steel or low carbon content) onto a hard concrete floor, the sound will be a dull thud. An HT (high tensile) bolt will sound with a brighter ring.

Much the same principle as rapping a steel bike frame tube with your fingernail to tell if it's a gas pipe job or made of something like Reynolds 531. Different steels have a different ring to them.

Older designs like the Land Rover engine mentioned by another poster somewhere upthread, will be heavy of construction, use cast iron as their principal material. The cylinder block will be low in distortion during assembly. The price of this over-engineering is an engine with a low efficiency as in low power to mass ratio. Great engines, will be readily tolerant of a deal of abuse, but of their time, and no longer valid for continuing production.

One man's over-engineering is another man's proper engineering! The vehicle that engine belongs to actually weighs less unladen than a modern BMW Mini, so the engine block may be heavy but the rest of the car isn't. It's also lasted almost 62 years and the block has only recently been rebored for the first time having probably gone to the moon and beyond in mileage terms.

 

[monkers]

I make a point of poking a bit of rag stretched over the end of a screwdriver into blind holes to ensure they are not full of liquid.



Much the same principle as rapping a steel bike frame tube with your fingernail to tell if it's a gas pipe job or made of something like Reynolds 531. Different steels have a different ring to them.



One man's over-engineering is another man's proper engineering! The vehicle that engine belongs to actually weighs less unladen than a modern BMW Mini, so the engine block may be heavy but the rest of the car isn't. It's also lasted almost 62 years and the block has only recently been rebored for the first time having probably gone to the moon and beyond in mileage terms.

Kitchen would probably be better.

The note produced depends on size and shape. Worth experimenting actually to develop familiarity.

Market forces I'm afraid. That engine could not meet the requirements that engineers are obliged to work to. Also everything is performance driven these days, it just wouldn't sell.

 

[SheilaH]

Wow, some of you are really lucky with your bike shop mechanics who have special torque calibrated hands.

I do all my own mechanic work precisely because at least half of my bikeshop experiences have led me to realise quite a few bikeshop mechanics are pretty careless, and some are bone stupid.

Torque wrench every time for me. Strict observance of rec. torque of parts. Extra care taken with anything carbon that is crushable. Pastes used to help prevent slippage etc.

 

[keithmac]

I would say in 25+ years of working on engines I've never had one that required the head bolts re-torquing. Some of the angle tightening sequences are amazingly tight, (waiting for the treads to fail tight!).

As for the OP, you should have marked the bolt head position, undone the fastener then re torqued to correct torque and checked position.

I have a few Snap-on torque wrenches, a lovely Techangle Digital one bought recently BUT they don't come out for every single bolt. 25+ years you get a feel for correct torque.

Would be interesting to see how accurate a cheap and cheerful torque wrench is, maybe a false sense of security.

I've seen customers manage to snap bolts off using torque wrenches, surely there's a point where you'd stop and check rather than plowing on?.

 

[Foghat]

Anyway, hope this helps

Thanks for that - interesting post.

bought a Mini Metro when they first came out

Back when they had a different-shaped gearstick?

 

[monkers]

Thanks for that - interesting post.



Back when they had a different-shaped gearstick?

I've never owned one, but if I remember the early ones with the A+ engines had a long straight stick, the design changing when they moved over to the 'K' series engine. Does that sound right?

 

[Foghat]

I've never owned one, but if I remember the early ones with the A+ engines had a long straight stick, the design changing when they moved over to the 'K' series engine. Does that sound right?

I've no idea. It was just an excuse to post a link to my favourite comedy line of all time!

Having said that, one of my late 1980s French Alps pass-storming trips was conducted in a Metro - two of us with two bikes. Frames and rear wheels on the back seat and in the boot respectively, front wheels and luggage on the roof.

It was my friend's car, and as it happens I got very acquainted with its gearstick on this trip - partly because I drove it back for him to England from Grenoble having left him to have another holiday down on the southern canals. In the Alps, going down the mighty Col de L'Iseran, the brake pedal had, terrifyingly, started going all the way to the floor before actuating, but that rectified itself after stopping to let the brakes cool down.

But on the journey down there from England, I had actually ended up spending an inordinate amount of time far too closely involved with the damned gearstick. A French girl had approached us on the ferry asking for a lift to a station some way into France from Dieppe. I said "well, sure but it's a tiny car full of bikes and stuff and the only place you could sit would be on the roof.....or the front seat with me". This didn't faze her in the slightest, and being a young chap eager to get acquainted with French girls, of course I was only too keen to facilitate the request, particularly if it meant enforced jostling with one at close quarters.......

So we set off from Dieppe in the early hours of the morning as usual, having agreed to set her down at Reims station. But when we got to Reims, it was still early, and she asked to carry on with us further down France. So we said "ok, how about Troyes?" Troyes was agreed but, you guessed it, Troyes came and went and she wanted to carry on......her destination was Marseilles. Being young and skint, we were using N-roads all the way, to avoid the autoroute tolls, so things were slower and more winding than making the trip these days. The advantage of driving through the night was that the roads were empty.

Now, several hours of front-seat jostling along these roads was starting to wear a bit thin, despite the upside. And I was getting substantially brassed off with that bloomin' gearstick by now. So by the time we got to Dijon, the discomfort was so great that I decided we'd take her to Dijon station, and this time it's definite. Well, we pulled up outside the gare, escorted her to the ticket office and made sure there was a suitable train for her to catch, and that she had the money, and strolled back to the car, me looking forward to a small front seat all to myself again and some relief from the gearstick (which I had kept knocking out of gear as I dozed, much to my friend's chagrin).

But lo and behold, just as we were pulling away, I spotted the girl in the wing mirror, coming towards us with her backpack. I'm sorry to say I told my friend to put his foot down and get out of there sharpish.

Well that's Mini Metro gearsticks and me!

 

[weareHKR]

From torque wrenches to Mini Metros