Grade 8.8 Guibo bolts

[lolcantturn]

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?

[Jafxod]

No way


Sub'd

[lolcantturn]

http://forums.bimmerforums.com/forum/showthread.php?t=1698686

Actually it wasn't a question of "Will it work or not" Jim, it was a question of is it good enough.

;)

[Jafxod]

I know im just being silly. Any idea where the rest of my guibo bolts are? Theres three on the guibo on my work bench.

[nando]

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.

[Sagaris]

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.

[Jafxod]

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

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.

If that was shorter I would sig that

holy fuck

[lolcantturn]

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.

Holy fuck legitimately shit myself

Amazing post. Thanks

[Kershaw]