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what grade should engine support bolts be ?


what grade should engine support bolts be ?

Old 03-16-2007, 11:32 AM
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I contacted Hillman Fasteners (large supplier for typical hardware store). I spoke with their quality engineer regarding the shear strength of their 7/16" stainless bolt. He indicated it was 6,300#'s. The bolts are ~ a grade 5 bolt. They tested from 100,000 to 150,000# (grade 5 is 120,000).

For the engine mount at the L bracket that would be a shear situation. 6,300 * 12 bolts = 75,600#'s.

Assume 5 G's of force from big wave:
1,200#'s * 5 = 6,000#'s for engine

Assume safety factor of 4:
75,600 / 4 = 18,900#'s

Seems like that should hold and still have room if assumptions are off a little.
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Old 03-16-2007, 11:20 PM
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I would never argue a stainless bolt is a tough as Grade 8 but this logic sounds reasonable. I would also assume that if the bolts were replaced with new on each and every R&R, the chances of shearing would be even smaller. Factor in larger diameter than 7/16ths and get an even smaller chance.

Thanks RV
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