Dennis, Your number of 7500 lbs confirms my number of 7200 lbs. That just seems incredibly high considering the OEM decided that 2 bolts would be required. It also seems ridiculous that one of them broke. I am at a complete loss as to how that would have happened.
Josh On Tue, Feb 23, 2021, 12:00 Dennis C. via CnC-List <cnc-list@cnc-list.com> wrote: > I'm guessing the thread degradation doesn't have much effect on the > strength as long as the shaft is not damaged. Having said that, the shear > strength of a M12 10.9 hardness bolt is about 7500 lbs. > > Did I win? What's my prize? Can it be shipped or do I need to pick it > up/sail it home? > > Dennis C. > Touche' 35-1 #83 > Mandeville, LA > > On Tue, Feb 23, 2021 at 9:42 AM Josh Muckley via CnC-List < > cnc-list@cnc-list.com> wrote: > >> Engineering discussion for the group. >> >> Here's the background. For about 9 years I have known about having 1 of >> the 2 bolts broken on the forward starboard engine mount. These bolts hold >> a piece of 1/2 inch plate steel which was bent at a 90° angle to the >> vertical side of the engine. This creates a horizontal shelf. The shelf >> then rests directly on the vibration dampening mount which is then bolted >> to the boat. Periodically, I have made attempts to extract the bolt but >> only a few days ago was I finally successful. The bolt was a M12x1.75. I >> don't know what hardness the OEM called for. Years ago when I discovered >> the broken bolt I was quick to replace the remaining good one with one >> having a hardness of 10.9. For a fresh start, I now intend to replace both >> of them with new and again a hardness of 10.9. In removing the old bolt, >> my drill hole was off center and ended up cutting some of the threads. I >> approximate not more than 1/4 of the thread integrity was compromised. >> >> https://drive.google.com/folderview?id=15GCOH3qKIWXl1lmjsbZqsf-ECGCrl1fN >> >> Here comes the question(s). Just for kicks, I decide to attempt to >> figure out what the sheer strength of the engine mounting bolts are >> individually. I came up with an answer but would like hear what the group >> comes up with. >> >> I also now have a bunch of other questions tumbling around like: How >> much weight would it take to break one? How much margin to failure did I >> have while operating for the last 9 years? What could have possibly caused >> this bolt to break prior to my ownership? Theories and ponderings are >> welcome. >> >> With 1/4 of the threads degraded on the newly available bolt hole, I plan >> to only torque the bolt to ~50% of max (90 ft-lbs) which would be ~45 >> ft-lbs. I'll also make sure that the lock washer is fully collapsed but >> I'm confident that that will happen well before final torque is reached. >> In sheer, I believe this bolt is providing as much or more strength simply >> by being there than anything to do with its torque. All though, I have >> heard the engineering theory that (when built appropriately) the bolts >> apply the pressure which creates the friction to prevent the pieces from >> moving in sheer. Under this argument the 2 pieces of metal don't actually >> ride on the bolt shank specifically, and the surface area where the 2 >> pieces touch is of particular importance. Looking at the engine castings, >> it would appear that maximizing surface area contact was not considered. >> As such, I can only fall back on my previous thought that the bolt shank is >> in fact carrying the load in sheer and torque is more or less irrelevant >> except for the purpose of keeping the bolt tight. I'm also aware of >> various thread repair options but in the awkward location I am fearful that >> I would cause more damage than good by attempting any of them. >> Particularly if the value added by the second bolt truly is its presence >> not its torque. >> >> All thoughts and insights are encouraged. >> >> >> All the best, >> >> Josh Muckley >> S/V Sea Hawk >> 1989 C&C 37+ >> Solomons, MD >> Thanks to all of the subscribers that contributed to the list to help >> with the costs involved. If you want to show your support to the list - >> use PayPal to send contribution -- https://www.paypal.me/stumurray >> Thanks - Stu > > > > -- > Dennis C. > Touche' 35-1 #83 > Mandeville, LA > Thanks to all of the subscribers that contributed to the list to help with > the costs involved. If you want to show your support to the list - use > PayPal to send contribution -- https://www.paypal.me/stumurray Thanks > - Stu
Thanks to all of the subscribers that contributed to the list to help with the costs involved. If you want to show your support to the list - use PayPal to send contribution -- https://www.paypal.me/stumurray Thanks - Stu
