Neil, It was awkward to see and corroded over. As best I can recall, it appeared the same way as any bolt I've ever broken by applying too much torque. It was definitely not a flat break across the face. The resulting diagonal face added significant difficulty in getting drill started.
Josh Muckley S/V Sea Hawk 1989 C&C 37+ Solomons, MD On Wed, Feb 24, 2021, 21:51 Neil Gallagher via CnC-List < cnc-list@cnc-list.com> wrote: > Josh, > > Did you happen to get a look at the broken bolt looking across the face of > the break? Good possibility it was a fatigue failure which occurs at > stresses well below the breaking strength, in which case you can sometimes > see the "beach marks" as the failure works its way across the section. > > Neil Gallagher > Weatherly 35-1 > Glen Cove, NY > > > On 2/24/2021 8:47 PM, Josh Muckley via CnC-List wrote: > > 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 > > > 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
