I got pretty good quality grade 8.8 guibo bolts from Loews on my E30 M50 swap. It's a small guibo so they're 17mm. I haven't clutch kicked or anything as I'm kind of scared, but is this enough?
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Grade 8.8 Guibo bolts
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Actually it wasn't a question of "Will it work or not" Jim, it was a question of is it good enough.
;)Originally posted by TSI♫ Rust flecks are falling on my head...♫OEM+
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I hate to get overtechnical, but 8.8 isn't a "grade", it's a "class". SI units (metric) vs SAE (imperial)..
but I'd think they'll be fine. I generally don't like generic bolts because the protective coatings aren't as good as BMW original bolts, but the strength of the steel shouldn't be an issue.
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For single shear with (6) bolts at a threaded diameter of 10 mm. Assume your engine output is 200 ft-lb of torque for calculations sake (271 Nm). Multiply that by a Getrag 260's first gear ratio of 3.83 to give a max torque of 1038 Nm. Suppose the distance between the centerline of the flex-disk to the centerline of the bolt is 30 mm (0.030 m) gives a force of 34,600 N divided by (6) bolts = 5767 N per bolt.
The shear stress on one bolt would be Force/area with an area of
pi*0.005 m^2 = 7.9x10^-5 m^2
Shear stress = F/a = 5767 N / 7.9x10^-5 m^2 = 73,000,000 N/m^2 = 73x10^6 Pa = 73 MPa
The yield strength of a class 8.8 bolt from http://www.boltdepot.com/fastener-in...ade-Chart.aspx is 640 MPa
This is assuming that the flex disk, clutch slip, and driving style makes shock loading negligible (not sure how true this may be). I guessed on the radius of the flex-disk.
According to these calculations your safety factor is 8.7 and that bolt will hold up fine.
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Originally posted by Sagaris View PostFor single shear with (6) bolts at a threaded diameter of 10 mm. Assume your engine output is 200 ft-lb of torque for calculations sake (271 Nm). Multiply that by a Getrag 260's first gear ratio of 3.83 to give a max torque of 1038 Nm. Suppose the distance between the centerline of the flex-disk to the centerline of the bolt is 30 mm (0.030 m) gives a force of 34,600 N divided by (6) bolts = 5767 N per bolt.
The shear stress on one bolt would be Force/area with an area of
pi*0.005 m^2 = 7.9x10^-5 m^2
Shear stress = F/a = 5767 N / 7.9x10^-5 m^2 = 73,000,000 N/m^2 = 73x10^6 Pa = 73 MPa
The yield strength of a class 8.8 bolt from http://www.boltdepot.com/fastener-in...ade-Chart.aspx is 640 MPa
Assuming that the flex disk makes shock loading negligible (not sure how true this may be) you will be fine. YI guessed on the radius of the flex-disk.
According to these calculations your safety factor is 8.7 and that bolt will hold up fine.
holy fuck
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Originally posted by Sagaris View PostFor single shear with (6) bolts at a threaded diameter of 10 mm. Assume your engine output is 200 ft-lb of torque for calculations sake (271 Nm). Multiply that by a Getrag 260's first gear ratio of 3.83 to give a max torque of 1038 Nm. Suppose the distance between the centerline of the flex-disk to the centerline of the bolt is 30 mm (0.030 m) gives a force of 34,600 N divided by (6) bolts = 5767 N per bolt.
The shear stress on one bolt would be Force/area with an area of
pi*0.005 m^2 = 7.9x10^-5 m^2
Shear stress = F/a = 5767 N / 7.9x10^-5 m^2 = 73,000,000 N/m^2 = 73x10^6 Pa = 73 MPa
The yield strength of a class 8.8 bolt from http://www.boltdepot.com/fastener-in...ade-Chart.aspx is 640 MPa
This is assuming that the flex disk, clutch slip, and driving style makes shock loading negligible (not sure how true this may be). I guessed on the radius of the flex-disk.
According to these calculations your safety factor is 8.7 and that bolt will hold up fine.
Amazing post. ThanksOriginally posted by TSI♫ Rust flecks are falling on my head...♫OEM+
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