gadget Posted April 24, 2013 Share Posted April 24, 2013 The threads that hold the caliper bolts in my swivel housings have had a hard time and i wondered about drilling them out and using coil thread inserts, but as we're talking brake parts here i was dubious. Let the experiment begin! I drilled a handful of holes in some scrap steel and put inserts in and using the old caliper bolts and spacers i tested the inserts to destruction One bolt lost its threads at around 175NM. One insert pulled through, stripping the steel threads at 225NM One insert deformed and became useless at 235NM And bolt could be tightened and re-tightened to 210NM without any obvious problem. After that i was happy enough to use them for the caliper bolt threads. Hopefully that will help someone else who might be pondering the idea. Quote Link to comment Share on other sites More sharing options...
landroversforever Posted April 24, 2013 Share Posted April 24, 2013 Interesting to see someone actually do a test Quote Link to comment Share on other sites More sharing options...
gadget Posted April 24, 2013 Author Share Posted April 24, 2013 Interesting to see someone actually do a test I needed convincing before i went down the thread insert route. The max torque i found listed for a 12.9 M12 bolt was 187NM. The failures were in the right region Quote Link to comment Share on other sites More sharing options...
landroversforever Posted April 24, 2013 Share Posted April 24, 2013 We use them a lot at work for stronger and longer lasting threads in aluminium Quote Link to comment Share on other sites More sharing options...
Tanuki Posted April 24, 2013 Share Posted April 24, 2013 Properly-installed, Helicoils are great. They can actually be better than a thread cut direct in the parent metal. And it's good to see you're actually testing your work and generating some sensible metrics on its quality. Alas I've seen rather a lot of improperly-installed Helicoils. It doesn't seem to be the load torque that fails them - it's more the effect of repeated shock-loads. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted April 24, 2013 Share Posted April 24, 2013 We use them a lot at work for stronger and longer lasting threads in aluminium And us....Iron castings too for some reason... Quote Link to comment Share on other sites More sharing options...
Maverik Posted April 25, 2013 Share Posted April 25, 2013 Lovely bit of testing, I like it when people think like that very helpful. Mav Quote Link to comment Share on other sites More sharing options...
heath robinson Posted April 25, 2013 Share Posted April 25, 2013 That's good to know, and makes me feel better about a few repairs I've made using helicoils. It's always been as an emergency fix, so without the time to test them first. Quote Link to comment Share on other sites More sharing options...
Maverik Posted April 25, 2013 Share Posted April 25, 2013 I worked briefly for a company that made infrared thermomenter devices for mounting in Tornado GR3 for the gas turbines, it being a RR client the QA was pretty strict, I remeber all the Ali and titanium caseing bolt holes where always tapped out and had SS helicoils inserted, I presume they give a higher reliability in thread strength, never thought about it till now. Mav Quote Link to comment Share on other sites More sharing options...
edessex Posted April 25, 2013 Share Posted April 25, 2013 I've been considering this, but the idea of thread inserts for brakes worries me! What brand inserts did you use? Quote Link to comment Share on other sites More sharing options...
gadget Posted April 25, 2013 Author Share Posted April 25, 2013 The inserts came in the Neilsen kit. There are no identifying marks on the coils, so i suspect that they're from the same supplier as Silverline, Sealey, Rolson etc. Quote Link to comment Share on other sites More sharing options...
elbekko Posted April 25, 2013 Share Posted April 25, 2013 I've been considering this, but the idea of thread inserts for brakes worries me! Why? There is very little force in the direction of the thread, it's pretty much all shear force. The only thing that you need to worry about, as with a regular bolt, is it backing out. Quote Link to comment Share on other sites More sharing options...
edessex Posted April 27, 2013 Share Posted April 27, 2013 I know the theory is good, but sticking a little coil of wire in a hole to hold a brake caliper on just sounds iffy! But as its common practice, rather than drilling and tapping for a larger bolt, I'm happy to give it a go! Are the caliper bolts M12? What length coil insert would I need? Quote Link to comment Share on other sites More sharing options...
Adam001 Posted April 27, 2013 Share Posted April 27, 2013 I know the theory is good, but sticking a little coil of wire in a hole to hold a brake caliper on just sounds iffy!But as its common practice, rather than drilling and tapping for a larger bolt, I'm happy to give it a go! Are the caliper bolts M12? What length coil insert would I need? No need to worry about helicoils, they are often stronger than simply using the parent material, especially with cast metal and ally etc. Think about stud and nuts...that is almost identical to a helicoil, it removes all torsional strain from the parent material, leaving purely a tensional force. with the helicoil taking the torsional friction force. Quote Link to comment Share on other sites More sharing options...
gadget Posted April 27, 2013 Author Share Posted April 27, 2013 I know the theory is good, but sticking a little coil of wire in a hole to hold a brake caliper on just sounds iffy!But as its common practice, rather than drilling and tapping for a larger bolt, I'm happy to give it a go! Are the caliper bolts M12? What length coil insert would I need? I've seen two types of bolts in front calipers. Both M12 but either fine or standard pitch. The 1.5D length coil was perfect for my swivel housing thickness. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted April 27, 2013 Share Posted April 27, 2013 Having used hundreds, if not thousands in all sizes up to M12 during rectification on new vehicles, I'd have no qualms about using them for calipers. Mo Quote Link to comment Share on other sites More sharing options...
edessex Posted April 27, 2013 Share Posted April 27, 2013 Mines an '85 110; pretty sure its not fine pitch. Also need to do a cylinder head on an old mower, so I better start looking for helecoil kits... Quote Link to comment Share on other sites More sharing options...
Orgasmic Farmer Posted April 27, 2013 Share Posted April 27, 2013 I have helicoiled a spark plug into an alloy head and that held fine. Would imagine that qualifies as extreme shock loading? Quote Link to comment Share on other sites More sharing options...
guyadawson Posted January 4, 2014 Share Posted January 4, 2014 Sorry for the hijack, but how much ( or rather little) damage would a caliper mounting thread needed to have sustained before it needs remedial action? When I removed the caliper mounting bolts on my RRC, there were some horrid noises and some bits of thread ended up on the floor. Looking in hole, there in no thread for the first 1-2 mm. Quote Link to comment Share on other sites More sharing options...
gadget Posted January 4, 2014 Author Share Posted January 4, 2014 If the rest of thread is in good condition i'd not be too worried about the first 1-2mm being bare so long at it torqued up correctly. I'd probably grab a spacer and torque the bolts up to spec a few times and then check the threads again. If any further damage is obvious i'd probably helicoil the thread. Quote Link to comment Share on other sites More sharing options...
landroversforever Posted January 5, 2014 Share Posted January 5, 2014 If the rest of thread is in good condition i'd not be too worried about the first 1-2mm being bare so long at it torqued up correctly. I'd probably grab a spacer and torque the bolts up to spec a few times and then check the threads again. If any further damage is obvious i'd probably helicoil the thread. To get full strength in the joint you need 1.5x diameter of the bolt worth of thread in the hole. Quote Link to comment Share on other sites More sharing options...
miketomcat Posted January 5, 2014 Share Posted January 5, 2014 To get full strength in the joint you need 1.5x diameter of the bolt worth of thread in the hole. Not disagreeing with you but why is a nut only 1x diameter then. Mike Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted January 5, 2014 Share Posted January 5, 2014 There's some elastic 'give' in the material as you apply tension - it's actually only the first two or three threads which are doing the 'work', the shear drops away very quickly from there. (Think about a straight pull on a rubber bolt into a blind thread in a rubber block, both parts would deform as near to the surface as possible.) The need for 1.5D allows max elastic deformation before yield in most conventional materials. Since cast iron is much stiffer and more brittle / less elastic, I'd expect you'd be able to allow less than 1.5D for the same strength join. Quote Link to comment Share on other sites More sharing options...
AMB Posted January 5, 2014 Share Posted January 5, 2014 We use helicoil inserts as standard on aircraft equipment. Usually much stronger than the base material. Only practical issues experienced where when a supplier tried to fit inserts into too large a hole or did not screw in far enough (leaving a protruding tang of helicoil above the surface). On investigation, the oversize hole was found to have been caused by drilling at too high a rate causing judder. In both cases the coil pulled out under load. Don't try and drill out in one pass. If you do, it can easily end up oversize with a weaker end result. Rather than scrap some very expensive machined castings we also investigated using double inserts. They worked a treat, massively strong. Now standard repair/refurb practice. Quote Link to comment Share on other sites More sharing options...
heath robinson Posted January 6, 2014 Share Posted January 6, 2014 Double inserts? Do you mean double depth? Quote Link to comment Share on other sites More sharing options...
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