Broken engine mount screw-tapped to big
Hello everyone, my trouble is consistent with my new hobby. I came back from a ride to see that my engine mount screw on rear of engine was missing....Wait a minute its not missing its broke inside of the engine case. Ok , figured out I needed to drill screw out since it was broke deep inside of case. Drilled out, bought all thread m6-grade 10.9 so this would never happen again, bought tap and die metric set. Came home cut my engine mount bolts from 1 meter all thread, screws cut perfectly. first screw went into engine mount hole that was fine, tapped the other hole but now it looks bigger than the other one ... So now my new bolt slides into the hole without grabbing the case.....once again I am in another dilemma.....I found helicoils at hf for 4 bux, they have 3/8 and 1/4 ,not sure which one to get and it only comes with heli coils, no tap no thread starter tool just coils....can I use my metric tap set to tap the hole for the helicoil to fit in or do I have to use a special tap that comes with more expensive kits on the net?