Stripped V6 Main Bearing Bolt Hole: How screwed am I? (Page 2/2) reinhart FEB 09, 03:12 AM Thanks for all the feedback and tips. I went ahead and ordered a helicoil M11-1.5 tap which should arrive on Monday. I didn't feel too comfortable using multiple 1x (11mm) threads in the hole as that could result in gaps between the two or other problems at least in my imagination. I was able to find a 3x (33 mm) length helicoil for sale at Oreilly's for a great price (cheaper than online outlets even before shipping). I can trim it down to whatever length I need or just thread the entire cavity, (The bolt shoulder diameter is smaller than the thread diameter so that isn't a problem. I should be able to dive into this next week. I was able to use a feeler gauge to determine the existing block thread is about 22 mm and the bolt engaged about 14 mm. I considered buying a longer bolt but still not too confident with just 6 mm of good thread to hold it in and it could introduce other issues like the bolts I found had 12.9 hardness ratings which would affect the torque and clamping force numbersvs the old one. As far as the top end, I guess I'm gambling a bit that the top end of the block is fine. Based on how little the engine was run after the problem blew up, so to speak, I hope it will be just the valve lifter lost its marbles. If the lifter hole is damaged, I imagine I can figure out a way to tap the hole for a time-cert and then drill out the inside threads away, or JB Weld it or something. I'll jump off that bridge when I get to it. I may be wrong but I don't think the lifter is seeing an extreme amount of force to unseat it from the lifter hole. I could also perhaps add some sort of spacer in the hole between it and the lifter. I'll jump back to that thread when I get this squared away. I figured this is enough off topic that anyone doing a forum search later may not have any interest in anything other than how to fix a stripped main or head bolt hole. BTW I did eventually find one other thread in the forums where someone fixed a duke stripped main hole with a helicoil. He said it was fine torquing it and getting the engine running again, but didn't get an update later on. The video was a machinist that tapped an aluminum block using about 5 different methods. He then compared the holding strength in tightening the bolts before failure and then also the clamping force until failure. Helicoil was much better than the time-sert in both categories and actually stronger than the original thread. I think it was something called Big-cert that did slightly better than helicoil in one category but the difference was negligible compared to the effort that would be required in my circumstance to try that. Anyone have an opinion on using red threadlocker on the outer edge of the helicoil? reinhart FEB 09, 03:15 AM Also I'm not too concerned about drilling debris. I'm coming into the hole from the underside, the hole is a dead end at the top and there's nothing below the hole. I can tape a piece of newspaper over the bottom of the engine as well with just that one hole open at the bottom to drill. Will FEB 10, 04:25 PM quote Originally posted by reinhart: I was able to use a feeler gauge to determine the existing block thread is about 22 mm and the bolt engaged about 14 mm. I considered buying a longer bolt but still not too confident with just 6 mm of good thread to hold it in and it could introduce other issues like the bolts I found had 12.9 hardness ratings which would affect the torque and clamping force numbersvs the old one. Rule of thumb is that for a steel bolt threaded into a steel part, the bolt needs a minimum of 1d in thread engagement to be able to get to the highest preload the bolt can take. Threading into softer materials requires more thread engagement. quote Originally posted by reinhart: The video was a machinist that tapped an aluminum block using about 5 different methods. He then compared the holding strength in tightening the bolts before failure and then also the clamping force until failure. Helicoil was much better than the time-sert in both categories and actually stronger than the original thread. I think it was something called Big-cert that did slightly better than helicoil in one category but the difference was negligible compared to the effort that would be required in my circumstance to try that. Yeah, there are a whole bunch of ways to cheat that or screw up. Since you haven't posted a link to the video... quote Originally posted by reinhart: Anyone have an opinion on using red threadlocker on the outer edge of the helicoil? Not a good idea. reinhart FEB 11, 06:16 AM The parts arrived Thursday instead of Monday so got to work on it today. I actually spent about 8 hours doing this including an hour trip to try to find a square head socket (ended up getting a 12 point 8 mm) and an 11mm bolt (which no one carries). There was a lot of measuring and double measuring and trepidation involved. The operation was a success. I was surprised how easy the drilling went. Could have done it in 5 min but took my time and it took 10. I was going to drill a slightly larger hole for the unthreaded part but realized how thin it was going to make the main wall between the bearing and the bolt hole so nixed that idea after about 1/8". I don't think anyone that was suggesting time-certs would say it's a good idea if they saw how thin the wall would be to get a cert in there which takes a slightly larger hole than a helicoil. The tap I took nice and slow. I was surprised how it took a little more effort than I was expecting. Used a pretty long T-handle for sockets and had to buy an 8 point socket to adapt the tap's square head. I had to tap about 40 mm to get past the first 14 mm which had previously been unthreaded and add 26 mm more. Finally the helicoil. The kit came with a covering that goes over the tool that the helicoil threads into. That covering was useless. It was good at trapping the coil inside it and not releasing it. I don't know exactly how it would have been helpful even if it had worked and not just jammed up. It was quite simple to just start the helicoil loose into the bolt hole and turn in about 2 coils and then thread the insertion tool inside the helicoil and continue turning it in until it bottomed out. I had to modify the tool because the shoulder was about twice the diameter of the bolt and only allowed for about 25 mm insertion and I needed 40mm. I had to grind away the shoulder and basically make it the same thickness as a bolt for 50 mm. I also installed a full 33mm helicoil. The bolt took a lot more force to turn into the coil but it is very strong. It feels much stronger than the other holes so I feel like it would be the last to strip out if any bolt were to strip out in the future. I had no problem cranking it up to 70 ft lbs. I suspect the threads are much thicker which is why the bolt had to work so hard to turn in due to the extra friction. All in all, it wasn't too bad. Much less difficult than I had imagined in my mind. I was fortunate that the bolt hole in question was the one I would have chosen to have to operate on if I had to choose any of the 8 holes. It was the front #3 main bolt. Nothing was directly below so had no problems getting the drill and tools in there. Thanks for all the advice and help. Notorio FEB 12, 06:16 PM quote Originally posted by reinhart: All in all, it wasn't too bad. Much less difficult than I had imagined in my mind. I was fortunate that the bolt hole in question was the one I would have chosen to have to operate on if I had to choose any of the 8 holes. It was the front #3 main bolt. Nothing was directly below so had no problems getting the drill and tools in there. Thanks for all the advice and help. Glad to hear that worked out so well. Soon you will be enjoying your Fiero once again Will FEB 14, 01:32 PM You broke the tang, right? reinhart FEB 15, 06:24 AM Nah no need. Based on my calcs, t is literally 9mm past the end of where the bolt would stop. Assuming a few mm of stretch still has 7mm of space. I actually did try to hit it out but it was close to the end of the hole.and didn't want to easily break off and I didn't want to risk dislodging the threads. Will FEB 16, 08:08 AM Good to hear you got it fixed. You may want to use a filter magnet to capture any chips you may have missed when cleaning it. reinhart FEB 17, 02:54 AM I have a magnetic drain plug.