Yes, there is a lot of info on repairing the common snapped exhaust stud bolts (the front and back ones) but I cannot decide which method to take.

I have attempted to drill out the bolt and remove with extractors, but that didn't work.  So I have drilled it out further.  I have used a 1/4" drill bit to drill out a hole in the stud.  It does not appear I have gotten into the aluminum (a magnet picks up the shavings).  AND I haven't gone too deep yet.  

I would like to use a helicoil for this.  

Should I drill larger than the stock hole, ie) INTO the alumnimum head??

The hole I have now (1/4") would correspond to a M6 x 1.00 helicoil kit.  I know the stock bolt/stud was M8 x 1.25. 

I'd prefer to not drill anymore if possible (don't want to ruin anything).  

Will and M6 hold up for awhile?  

Or should I just drill into the head for an M10 bolt, and will this fit through the stock exhaust manifold flange hole?

I really thought about just leaving the broken stud, since my old engine's rear was snapped for years.

But this one is under the Thermostat housing, and I've read it can affect the sensors, and therefore the ECU and fuel mixture OR melt the cap and rotor.  Not to mention, I am trying to eliminate the fume smell as much as possible.

Never done anything like this before (first engine swap), really just want a running Z again at this point.  I will say though, that I'm a decently skilled and experienced "mechanic" from working on my own cars. 

Thanks for any help~

never fun to put it back together with broken/missing fasteners - a bunch of work and then you get leaks.

 i would drill it out for the M10 then widen the manifold hole if needed. key is to not go too deep...

11 minutes ago, ramsesosirus said:

I have attempted to drill out the bolt and remove with extractors, but that didn't work.  So I have drilled it out further.

The hole I have now (1/4") would correspond to a M6 x 1.00 helicoil kit.  I know the stock bolt/stud was M8 x 1.25. 

I'd prefer to not drill anymore if possible (don't want to ruin anything).  

Is the hole centered and perpendicular?  What didn't work with the extractor?  

On your way to "bigger" for an M10, the remains might come out.   You can't get to M10 without doing that anyway, so really all you can do is keep drilling, and/or get better extractors.

You want the stock size or bigger, so M6 isn't going to work.

For dill bits, have you been using left hand bits?

That's what worked for me a few years ago, started small & well centered, worked my way up a few sizes, and the stud backed out.

The extractors won't turn at all.  Feels like I would break them if I applied more force.   

Basically, drilling into the aluminum is ok/required to upsize the bolt, correct?  What is behind this stud (the front most exhaust manifold stud, under thermostat) oil passage, coolant, etc.?

Just found out I need to remove the power steering pulley from the crank so the fan doesn't hit it.  (280zx engine).  I hope those bolts don't snap... 

 Don't break them!  Is the hole too big to thread with a M8 heli-coil tap? If not, I'd buy the M8 Helicoil kit if that is original. Drill, tap and install a M8 helicoil. if the hole is already too big, you're probably looking at the next size up.

 Some alum. is going to be removed for a heli-coil or a larger bolt. Measure the depth of the hole and wrap a piece of tape around the drill bit the same distance from the end as the hole depth. Also possible to mark the bit with a Sharpie.

there is a tread somewhere about using some common chemical that eats steel but not aluminum. alum? maybe?

 

 Found it.  Jan. 31  "Alum for stud removal vs vinegar - garage experiment".  This is worth a try. Nothing to lose except a little time.

this is the video i was referring to. there is some foul language

 

 

 

Edited April 10, 20168 yr by sweatybetty

I tried it and namerow too.  Nothing significant happened.  It takes heat and lots of time.  Worth a shot but be careful.  Most of the videos are about small watch parts. These parts are huge n comparison.   The chemical reaction generates gases that might be flammable.

Don't expect magic.  It's been around for many years, and considering how many broken studs in aluminum have happened over those years, you'd think something so easy would be more popular.