doubts robustness snowmobile

[klrowner]

Good morning.
My name is fabio geremei and I am a fan of mechanics and engines in general.
I don't know if this is the right forum, maybe I'll ask you where I might be redirected, but I've seen that people here are very well prepared and professional.
I write to ask you a question about the installation of a magnet/motor wheel (kawasaki brand) on the motor shaft.
I have to reassemble the fly/magnets of a motorcycle on the motor shaft, said flywheel is bolted with a flange screw m10 at step 1 mm, on the motor shaft that in correspondence has a slight conicita' and on which is inserted a woodruff key, locked initially to 120 n-m to lay it on the conical portion, loosened the screw, then re-mounted first to 120m. Now for reasons I am not here to explain, but due to doubts about the execution, I have already proceeded 3 times to the operation, every time tightening and then disposing everything with a special extractor. the screw at every 175 clamp is prescribed on the workshop manual not to reuse it, then replace it with a new one.
The question I ask you is: As many times as you can proceed with this operation, being sure that the screwdriver is not damaged or weakened, taking into account that the engine shaft is hardened steel, according to an authorized Kawasaki workshop.
if necessary I can insert some photos, but I will send you to a link where you can find them together with the discussion about the procedure: mark's klr650 website - doohickey upgrade (idler shaft liver)thanks for any answers
fabio geremei
Bologna

 

[TETRASTORE]

Good morning @klrowner, the screw you described belongs to the category of critical screws, in this case screws fly, used habitually in the automotive and characterized by reduced dimensions but to endure high stresses without undergoing looseness whose effects would be detrimental to the integrity of the motor. their resistance class is usually never less than 10.9 and, in order to maintain reduced weights and dimensions, they are urged well beyond the canonical parameters (locking pairs) found in tabelle standard.
the normal screws used in standard assemblies are exploited in the field of the elastic limit for which, once the axial stress has ceased, the relative elongation that comes ceases and the screw returns in the initial condition for which you can reuse them several times.
In your case, however, the manufacturer, as often happens, probably designed that type of clamping to operate in the plastic field which means that the stretching immediately from the screw after the tightening to the maximum specified torque, will be permanent for which it is necessary to replace it after each disassembly.
a new screw you can tighten it n times to the minimum torque indicated without replacing it, but once you have applied the maximum torque indicated by the manufacturer, you must necessarily replace it (after disassembly) as it no longer has the characteristics of reliability required by the project.
often critical screws are also applied microencapsulated glue ( commonly called braking) requiring a high detachment torque thus avoiding accidental loosening; if present in your case, also this may be one of the reasons why the manufacturer requires the replacement of the screw, as some producers of screws that apply this treatment indicate a maximum number of avoidances (some up to 5) but it is obvious that given the criticality of that screw the designer imposes a much more severe limit to avoid even the slightest risk of loosening.

 

[Diego536]

@terastore yesterday as soon as I saw the thread I was writing a similar answer to your but, rereading the request, I understood (maybe wrong?) that @klrowner had doubts about the seal of the internal thread of the motor shaft (madrevite) and not on the screw that goes, as you rightly explained, replaced at every disassembly if so, according to me, it is difficult to understand the sealing limit of the thread on the shaft every time you proceed to the assembly...for this reason, probably, the assembly manuals distributed by the builder himself there is no indication

 

[klrowner]

thanks to the answer, my doubt concerns the mothervite, that is the threaded seat in the motor shaft, where the screw is inserted, that I, following the indications of the workshop manual, replace to every lock. Since I've already performed two or three times the clamping to the prescribed couple (175 n-m), I was wondering if that didn't weaken the thread of the mothervite.

 

[TETRASTORE]

the limitation provided in the instructions derives from the "stirification" of the screw while the mothervite solidarity with the shaft, in practice the threaded hole in the head of the shaft, is not involved in this problem. if there were any design limitations, given the importance of this component (shaft with threaded hole) and its high costs for replacement, you will surely find indications on the manual.

 

[klrowner]

the limitation provided in the instructions derives from the "stirification" of the screw while the mothervite solidarity with the shaft, in practice the threaded hole in the head of the shaft, is not involved in this problem. if there were any design limitations, given the importance of this component (shaft with threaded hole) and its high costs for replacement, you will surely find indications on the manual.

I also thought the same, but to hear more opinions maybe more than me reassures me