Hi I'm sure this is very obvious, but I can't find an answer via search. Why are there three torque settings in the service manual for some engine things? Always in the same pattern, mid, low, high. Is tightening a five stage process? Torque one, back off, torque two, back off, torque three?
Apart from the brake calibers which have an initial torque before applying the brake and then fully tightening, I have always assumed that the first figure specifies the required torque and the other 2 are the maximum and minimum values. There are some instances though that require sequential tightening, as in the cylinder head nuts where the stages are stated.
it could be that there are stretch bolts fitted. but you would expect there to be a notice telling you to replace the bolt, or measure it at least before instalation.
Where you have one line of values per component/fastener, the three figures are nominal/low/high torque figures. The low and high are usually 5% or 10%, so for the nominal 38Nm, you have a low of 34 and a high of 42. Where there are "stages" listed as per "cylinder head" for instance, the these are torqued down in three, increasing stages to ensure the heads go down square and you get a consistent pressure build up on the composite gasket. Again, the three figures listed against each stage are nominal/low/high. Rule of thumb; Always set your wrench to the nominal. The tolerance will allow for any discrepancy in the wrench' calibration or accuracy.
@nelly has stated all you really need to know about torque settings I'll just add my two Drachma's worth .... 1] You might have an " old school " torque wrench which gives a click , or a modern one that goes "beep" ..... Do not be tempted to give it a second pull ..... "just to be sure " ..... because you will then over tighten it . 2] keep an eye out for manuals which mention "angle torque" , where they specify an initial torque setting followed by an extra tightening ...... eg. by 90 degrees . I honestly don't know if that appears in any Ducati manuals , but in any case it is to allow for "stretch" in the fastener .
As I'm a pedant I need to add my deux Centimes too. The rotation angle is not to allow for stretch in the fastener, it's to put a known stretch (=tension) in the bolt. Bolts are just extremely stiff springs... A lot more here if you're interested... https://www.boltscience.com/pages/basics1.htm
