Ok, so my ears weren't deceiving me. Got some time to crawl up under the car this afternoon and see I'm missing a stud on #1:

Click to view attachment
Click to view attachment

I know it was there a week ago. Can't get any light and a camera up in there to take a picture of the inside, but from what I can tell the stud is not broken off and I don't see obvious signs of damaged threads. I wonder how common it is for it to back out like that (assuming that's what happened) - or did exhaust pressure rip it out (and damage the threads)?

What are my best options now? I guess I would need to establish that the threads are or are not damaged. If they are not, I guess I just need to get a replacement (M8 x 56, I think from the PET). If damaged, I guess it's assess how to repair. Should I simply try to pick up an M8 by 1.25 bolt from "Home Despot" to see if it will thread, or is that asking for more trouble?

Very strange indeed!

Did you locktite the original one?

No idea what would cause it. But if the stud didn't break off in there, I don't see anything wrong with your idea of trying an M8 X 1.25 bolt. If it starts to bind, give up and pick up a set of thread chasers. Run the chaser through the hole, install a new stud with red locktite and call it a day.

http://www.sears.com/craftsman-48-pc-sae-m...mp;blockType=G1

Hey Bob - good idea. I'm going to go ahead and order a new stud and see if it holds ok or binds. I never put this stud in, so I don't know if it was treated before. Should I do that with the new one?

Always something, never bored...

A bolt is probably not a great idea. Best bet would be to remove the exhaust from that side of the motor and inspect the hole where the stud used to be. If all is OK, use a new stud and nut.

Loctite won't really help, the head gets more than hot enough to kill any version of Loctite that I can think of.

--DD

It likely pulled the threads out last time you tightened it. I'd pull the exhaust and either tap for a 9mm/8mm step stud or a timesert.

Look at the bright side, at least it pulled out instead of snapping off.

New stud and nut on order. Travelling again, so I won't have time for a week or more to look at it. I think I'll try to see if the new stud holds, and, if not, it's on to other repairs. I though I was pretty careful when I tightened these, but of course it's seen more wear over the years than I know of so it could have been damaged previously.

Thanks for the advice.

Got back into town this evening and I have a new stud that arrived in the mail. After looking at it some more I think it's wise to remove the heat exchanger first, as suggested, and inspect / install the stud. I also ordered the oversize stud (just in case). Any advice for how best to install said stud?

saigon71/Bob Hill posted a recent thread where he had to drill out a broken exhaust stud. He made a "tool" to help the drill bit stay centered on the broken stud. I bet something from that thread would give some ideas for your situation.

Def remove the H.E. Determine the hole depth with the bit and wrap the bit with some tape. You don't want to go too deep.

So it was less than 90 degrees and I got home from work at a decent time, so I tackled it this evening. Got the HE out and installed two new studs after a little struggle getting them to thread properly. I used two new copper gaskets (that my son annealed after I taught him how) and used the "grease method" to keep them where they belong during HE installation. After some patient tightening I fired it up and it sounds better than ever. None of the loud "whop-whop-whop" at idle that had grown progressively gotten worse over the last month. Just a steady, throaty growl. In hindsight I probably didn't have a great seal on the gasket during initial install. The exhaust leak that was getting progressively worse may have contributed to some of my difficulty identifying and correcting my D-Jet issues as well (O2 sensor may not have always given me accurate readings). I just hope the studs hold ok. The whole setup seems fragile and troublesome even under the best of circumstances.

Thanks for everyone's help. Everything is awesome (again).