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11th June 2020, 19:31 | #21 | |
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Quote:
Preload of any threaded fastener is important, as when radial torque is applied what you are actually doing is applying torsional load to the fastener, and placing it in tension. As a rule of thumb, the preload should not exceed 75% of the yield value of the fastener. So when a 10.9 tensile strength cadmium plated bolt, is substituted by a 8.8 bright zinc plated one, the yield value is reduced by 68% of the original fastener, meaning the elastic limits of the fastener are easily exceeded as you have found. In short without delving too deep into semantics, the original fasteners are carefully calculated in design to use the minimum diameter of bolt to effect the correct clamping load to the joint. Substitution without understanding the concept that tension is the important factor, and the applied tension of two otherwise similar components, but of different tensile strength, fastened to an identical torque figure is completely different. Brian |
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11th June 2020, 20:09 | #22 |
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Hi Brian.
I'm annoyed at myself. I work in engineering and saw the bolts were marked up 8.8. I should have stopped the job. |
11th June 2020, 21:09 | #23 | |
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You are allowed to be with yourself we all make little mistakes now and then, what comes after is how you learn from them lets hope DMGRS will now remove these from sale with the arms and either add the correct ones or point purchaser in the right direction from where they can be sourced, hopefully you will be able to remove the snapped bolt without to much trouble.
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11th June 2020, 21:51 | #24 |
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With a new bolt this should hopefully be an easy task, once the pressure is off the bolt (As it will be when it has snapped) The threaded part shouldn't have too much resistance.
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11th June 2020, 22:45 | #25 | |
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I'll sort it, not impossible just much more work than it was supposed to be, and it's my Dad who is without a car for a few more days. DMGR's have acknowledged so they're are on it. This need sorting out for their sake as well, as a failure at another time could have much more severe consequences. |
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12th June 2020, 10:58 | #26 |
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may be quicker to remove sub frame and do it on the floor
macafee2 |
12th June 2020, 11:03 | #27 | |
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I would try and see if you can get a punch or a small chisel on the broken bolt to see if you can turn it enough to allow a small pair of long nosed pliers in.. Good luck.
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12th June 2020, 11:34 | #28 |
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would a screw extractor work? I imagine it would on the floor, I cannot remember how much space there is fitted
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12th June 2020, 11:39 | #29 |
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I had the same thing a few years ago with DMGRS and told him about it. Not only are they the wrong property grade, they have insufficient corrosion protection too. I would not sleep at night supplying inferior replacements for safety critical parts. It would seem a little knowledge could be dangerous.
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12th June 2020, 11:40 | #30 |
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Ben - here's a pic in case it helps.
1. Captive nuts as viewed from above the subframe. 2. Blow up of above (split) 3. Clearer view of the captive nut cage (lower arm shown) 4. Above taken from this wide shot (lower arm again) |
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