Hey everyone! I recently stripped a bolt hole on a transmission mount while working on my car. This was my first attempt at drilling out and tapping a new hole, using an M10x1.00 tapered tap and a 23/64" drill bit as recommended. I was careful and used lubricant while drilling, and it seems to have gone well since I can screw an M10x1.00 bolt in without much resistance. However, my concern is that the bolt won't fully torque down; I can still easily turn it with a hand socket. Is there something wrong here, and how can I fix it? Thanks for any help!
2 Answers
You might want to consider using a helicoil repair kit. Your current tapped hole diameter is likely close to 10mm. For an M10 helicoil, you would need to drill slightly larger, like 10.3mm, for the insert to fit correctly. This could give you a much stronger hold!
It sounds like you might have tapped the hole too large for that bolt. If you can keep turning the bolt without it tightening up, that's a sign. For an M10x1.00 bolt, a 9mm drill bit is ideal for tapping. The 23/64" bit you used is a little on the big side (roughly 9.128mm). So, you'll want to either re-tap the hole with the correct size or go with a different size bolt and tap combo.
Thanks for breaking that down! What bit size do you recommend I use then? I want to make sure I get it right this time.