Pulled the Y pipe out today because of exhaust leak that is noisy and smells in the cabin when not recirculating cabin air. 2 studs stayed in the engine block, not stripped. 1 stud came out with the nut, engine block threads OK, but 1 hole on the L side is stripped. Won't thread back in at all. What's my best option...

1. Drill and re-tap larger diameter? Seems to be plenty of material to support larger hole an re-cut threads. New Y-pipe and cat have large slots (15ish MM) Never done that before though, might be tricky to align drill bit and tap?

2. Helicoil? Never used these either.

3. There are 2 other holes with threads 90 degrees rotated from the original ones. Is there a way to get a 2nd flange around the pipe rotated 90 degrees to use these holes? They have threads same size as the original ones. 

4. Other ideas? I want to keep it as OEM as possible. i already have the replacement Y pipe and cat so I don't want to change that. 

Tap to 7/16th and install a 7/16th stud.

Or helicoil.  More work, more expensive, but then you retain metric stud if that's REALLY important to you.

For the $40 price difference, less work, and leaves more material for later and stronger (no helicoil) I use 7/16th stud.

Heli-coil. 

We use https://www.threadtoolsupply.com/

Get some EJ exhaust manifold studs from Subaru. 

GD

Edited July 8, 20196 yr by GeneralDisorder

I have used helicoils on mine, with good results.   Yes, make sure the drill and tap are perpendicular to the face.

Helicoil and 7/16 are both easy. Tap it and done. 

yes me too on mine. i got a helicoil and fixed it right up,  btw i make teh mistake and paid a lot for matching metric threads and pitch.  my friend had one that as metric but not the same pitch, and for one bolt on the car it would have beeen a huge savings to use his that he will never use after the one bolt he replaced.  so look around for the right drill bit and helicoil set  just match the stud with a correct nut and  your good to go.

 

Timesert is another option if you’re going long term and expect to remove the y pipe again. Pricey , but excellent. 

I ended up drilling & tapping new 12mm threads. Worked a treat! It's so quiet now! Thanks for the input all. 

M12 ? Did you need to increase hole size on flanges? Always good to quieten a burnt outflange gasket

No, my replacement Cat/Y pipe from rockauto has large holes in the flanges. They're like 15mm. I went larger diameter on the coupling bolts to the muffler too.