318 exhaust - stripped bolt threads & Time-Sert size?

[klarish]

a few questions.  I have a 318 with long tube headers.  Several of the threads on the driver side are stripped. 
what are the best studs to install?  What size do I need?
Time-Serts: what size do I need? do I need to remove the head from the engine bay or is it possible to repair in there?

[Solarguy]

Before you try thread repair, try a longer bolt.

[RUNCHARGER]

Hmm, if several are broken it's going to be a lot of work repairing them especially the drivers side in the car. Unless the head is something special I'd be tempted to replace the head. You'll end up pulling it anyway. The studs are 5/16".

[Burdar]

To find a replacement set of heads and have them gone through at a machine shop is going to cost you $400-$500.  That would be a last resort for me.  If longer bolts don't work, then I'd just drill out the holes and tap them to the next size.  You'll probably have to remove the headers and drill out the header flange.   I guess it depends on which bolts are stripped, but you shouldn't have to remove the head.  Use a short 90 degree drill.  I wouldn't use studs.  I'd put bolts back in it.  Studs will make installation/removal of the header very difficult.

[Chryco Psycho]

I doubt you can get them fixed in the engine compartment , you can just use Helicoils on all but the end holes as the holes are blind & do not seal water , the end ones would need timeserts to seal coolant .
If the heads are not special replacing them may be the best option & you could get better heads too such as the 87-92 swirl port 302 or 308 castings .
As above 5/16 is the original size , rehtreeading to 3/8 may be an option , you would have to open the holes in the manifolds slightly

BTW Welcome to the site from Panama 

[klarish]

I already have various size bolts frankensteined in there to keep the headers on. 

Looking to put studs on the ends to keep them sealed.  Based on another post I saw these studs would do it:
http://www.allensfasteners.com/detail.asp?Product_ID=23003A

The other stripped holes I can use Time-sert or Helicoils:
https://www.ebay.ca/itm/Time-Sert-03815-3-8-16-x-750-Carbon-Steel-Insert-10-Pack-/280789503724?hash=item41605bceec:g:Xr0AAMXQjWtRMPYd

So my options are
5/16" studs normally using Time-Sert on the ends, or drill/re-thread to 3/8" stud seems to be the way to go.

Any recs for threading tool(s)?  I'm looking to try to keep the head on.  Will pull off as last resort and keep my current heads.

[klarish]

which size Time-Sert? 3/8" or 5/16"  **Edit: that sounds like a dumb question. 
What I meant is is the 3/8" timesert for a 3/8" stud/bolt? Is it inner diameter or outer?

3/8"
https://www.amazon.com/TIME-SERT-8-16-Thread-Repair-0381/dp/B001JK23O6/ref=sr_1_12?dchild=1&keywords=TIME-SERT&qid=1600230319&sr=8-12

5/16"
https://www.amazon.com/TIME-SERT-16-18-SAE-Thread-Repair/dp/B0025MQ63Q/ref=sr_1_15?dchild=1&keywords=TIME-SERT&qid=1600230319&sr=8-15

[Chryco Psycho]

if using a timesert I would go back to stock size - 5/16 inside

[klarish]

@Chryco Psycho when installing the studs do I just put them in hand tight?

[Chryco Psycho]

I would use locktite on them so they stay in place when you remove the nuts & tighten them more than hand tight , you can use 2 nuts tightened together to tighten them in .