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In every manual for vehicles you will find bolt torque specifications. These are not willy nilly numbers just guessed at or printed for the fun of it. They are there because that is the amount of torque any given bolt should have to insure the part is held securely and won't loosen up under use. There are general numbers for most of the fasteners like a 6mm bolt is 7-9 foot pounds and then there are specific numbers for certain components like rotor bolt on the CM/CB 400/450 engines of 70-90 ft. lbs. When given a range, like the 70-90 ft. lbs., I use the middle of the range, 80 ft. lbs.
What happens if you don't torque something properly? Over torquing a bolt can cause it to shear off or it can pull the threads out of it's mating part, common for case mating bolts. Under torque will result in the part coming loose and potentially causing damage to it and it's mating part. Here's an example of what happens when the rotor bolt isn't torqued to spec.
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Yes, the woodruff key is beaten to death, the slot for the key is beaten out and the nose of the crankshaft is cracked. Now this engine needs a new crankshaft. I've done a temporary repair to get the bike back on the road with JB Weld to center a new key in position and take up the slack of the crankshaft. What started as a 15 minute rotor replacement turned into a 2 hour nightmare with hopes the crack doesn't continue or turn 90 degrees and have the nose of the crank shear off. The owners is looking into an engine replacement or an engine overhaul at this point. The PO had removed the stator at some point and the current owner did as well but failed to use a torque wrench. The PO actually removed the magnetic plate fixing screws on the rotor and didn't install all of them or even tighten the ones removed which cause a host of other issues.
There are 3 types of torque wrenches sold: pointer, gauge and click.
The pointer type is the least accurate since the value is determined by the angle the marking plate is viewed from.
The gauge type comes in analog and digital versions. Not familiar with the digital. The analog type is good but can be difficult to read the gauge in certain positions. You've got to be able to look directly at the gauge when using it. I understand there are some digital versions that 'beep' when torque is reached.
The click type is good as long as it re-calibrated periodically. The cheap versions found in places like Harbor Freight may be ok and then may not. You won't know until it's checked or something fails. I prefer the click type because I can feel the snap when torque is reached.
With any torque wrench it should be checked and calibrated periodically.
While a lot of us old folks use the feel method for any number of fasteners those with little or no experience should really get used to using a torque wrench. I have 3 different range ones, an inch pound, a 5-40 foot pound and a 30 to 200 foot pound. All click type.
 

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Good info Jim,

in addition,I have seen plenty of "experts" incorrectly using the click type by getting the click + one for good measure. Here are a couple of tips I swiped from Snap-On, I only send mine to the cal lab every two years.

As most torque wrenches are length specific, always grasp the torque wrench in the center of the handle. If two hands need to be used, place one hand on top of the other.

Apply torque in a slow, methodical manner and avoid sudden, “jerking” movements.

When the wrench signals (by clicking, beeping or lights) that a specific torque has been reached, stop pulling immediately.

After 5000 cycles or up to one year of use, whichever comes first, have your torque wrench inspected and re-calibrated by the manufacturer or reputable calibration service.
 

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Also click type torque wrenches should be set to their lowest setting for storage and they should be "warmed up" by selecting a moderate setting and pulling hard enough to "click it" several times before using.
 

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The fourth type is the electronic torque wrenches using a load cell.

A word of caution on them though ..... once you use one you will never want to use any other type.

On the Gold Wing boards there was a certified tool calibrator who had some great insights. Harbor Freight torque wrenches were quite accurate, certainly good enough for most motorcycle wrenching, calibration is really important for aviation certification or fasteners that need to be certified but after that he didn't find many that were out of range new or after use from any mfg.

Never heard of the warming up procedure or read about it. Given the temperature range tools get used at I can't see it making any difference.

Really the torque wrench is for getting a fastener into a range and in the case of multiple fasteners holding a piece in place having them all close to each other.

BTW the biggest complaint I have with low cost torque wrenches is the coarseness of the ratchet compared to say a Snap-on. The 3/8 flex head Snap-on I have also gives some advantages in tight spots.

At the price point a person can buy a torque wrench at these days there is no reason not to have one or two or three ....
 

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Have two Precision Instrument dial-type torque wrenches. Not as convenient as ratcheting wrenches but the are very accurate & there really isn’t much that can go out of calibration. They are also less sensitive to how you hold them.
 

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As a helicopter engineer, +1 on the maximum torque unless it's a castlated nut that requires a cotter pin. In this case it's minimum torque then reset the torque wrench to the max torque and align the hole with the next casltation in the clockwise rotation. If the torque wrench clicks before you get them lined up change the thickness of the washer and start again.
 

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Discussion Starter · #14 ·

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Discussion Starter · #16 ·
200 in/lbs is @16 ft/lbs which is just enough for the cylinder nuts. The oil filter needs 23 ft/lbs, the rotor calls for 17.4 and the engine mount bolts are 32 ft/lbs.
 
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