Replacement Stainless Steel Bolts

[COLOR=#373E44][FONT=&quot]WhileI was, before retirement, an engineer by profession, I’m wasn’t one that had todeal with mechanical component design so I need to ask here.[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]I’m amotorcyclist and, like many bikers, I want to replace the old, tarnished bolts onmy bike with stainless steel bolts. My problem is the torqueing of them toprovide clamping forces without overstretching them.[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]Allstainless bolt suppliers I’ve asked just say “Take your old bolts out, fit thes.s. bolts, lube them and torque to manufacturer’s spec.”. This is where I have theproblem. Many of the old bolts are marked as 8.8 steel with an accepted yieldstrength of 640 MPa, A2 stainless are 450 MPa.[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]If Iuse a figure of 65% yield strength to stay on the elastic part of the material’scurve and, say, an M8 bolt with stressed csa at thread root of 36.61 mm^2 (fromtables):-[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]For8.8 steel; 65% yield strength x csa = 15 kN clamping load. [/FONT][/COLOR]
[COLOR=#373E44][FONT=&quot]ForA2 stainless; 65% yield strength x csa = 10.7 kN clamping load. [/FONT][/COLOR]
[COLOR=#373E44][FONT=&quot]Doesthis make sense so far?[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]If I thenput those into the simplified formula Torque = ‘nut factor’ x bolt diameter xclamping force = kDF and using a ‘nut factor’ of 0.16 for lubricated bolts, Iget:-[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]For8.8 steel; T = 19Nm.[/FONT][/COLOR]
[COLOR=#373E44][FONT=&quot]ForA2 stainless; T = 14 Nm.[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]Thereforeif I torque the s.s. bolt to the 8.8 figure, it’ll be loaded to about 90%yield strength and maybe at risk of breakage or, alternatively, the maximumtorque I can apply doesn’t provide the clamping force necessary.[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]Isthere REALLY a problem or am I making a ‘mountain out of a molehill’?[/FONT][/COLOR]
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[COLOR=#373E44][FONT=&quot]Cananybody offer some more knowledgeable insight?[/FONT][/COLOR]

You math seems right as does your concern. In critical applications, like brakes or other essential places on the bike I would not change out the materials to something less capable. There is also a corrosion issue due to dissimilar metal contact at the point of installation (you bike is most likely aluminum). You might re-think your desire to have Stainless Steel bolts.

Maybe chrome plated bolt heads with the same strength rating??