This thread is in reference to my previous thread Exhaust Manifold/Catalytic Converter Replacement Advice.

I am in the process of replacing my exhaust manifold/catalytic converter and I had 3 broken bolts to deal with: one at the front by the fan, one in the lower middle area, and one that was broken beneath the head's surface at the very back by the firewall. Got the middle bolt out with a bolt extractor tool. Front bolt was coming out but the extractor tool was too fat to fit flush and I ended up snapping the bolt trying to square it up. Had to drill that one with a 1/8" Cobalt drill bit from Milwaukee (highly recommended, works great) and was able to get it out with my SpeedOut screw extractor bits. Obviously had to drill the last bolt as well, thinking that I would drill some and then it would screw right out like the previous one but it just wouldn't come out. I've been trying for 3 days now and it just wouldn't budge no matter how much I drilled. I've done everything: PB Blaster for about 14 days, blow torch, cutting oil, drilling slow, hand crank, but nothing. It was unbelievably hard to get the drill square all the way back there and I eventually got off-center.

I just spent an hour or two today drilling and drilling and I basically just shredded the bolt to bits without actually removing it. I think there is still some remnants left in the threads though because I can't get a new M8 bolt in there. I am sure that I have to Helicoil now but I noticed through my phone's camera lens what appears to be a crack in the very back of the hole. So my question is, am i completely screwed now, or is okay? I can't remember where because I've read some much about extracting broken bolts, but I think I remember someone mentioning the importance of being very careful back there. I really did try as hard as I could to avoid that but guess I didn't try hard enough. Picture of the crack below. Would appreciate your thoughts and recommendations on what to do next. Go get a Helicoil set and get it installed? Thanks


Manifold bolt hole – farthest towards the back by the firewall

 

Were you drilling for oil? Beyond 28mm max depth. Take your time and tap that hole(straight as you can) Drill bit 17/64-9/32 - Tap M8 x 1.25. After you get clean threads to install the stud, loctite.

 

Hey KU, sounds like a tough situation! I agree with Hummerz tap idea and think a good first option is using a M8x1.25 tap. If the tap can grab onto some of the original threads, it should clean out the remnants from the old stud. If you're unsuccessful with the M8x1.25 tap, I think using a Helicoil kit to re-drill, re-tap, and run the Helicoil in would be a great idea.

As far as the crack at the rear, I recognize how annoying it would be to know it is there, but I think you should be good assuming there is a good seal between the new stud and the threads in the head (maybe red high temp RTV on the threads?)

Keep us updated and nice work so far.

 

Ha. I wish I did hit oil. Need some oil $$ to pay for all of these parts and tools I am accumulating for this project. But I did use a few of the other bolt holes as a guide and taped off the drill bits accordingly so I don't really know what happened. I guess hours of drilling will do that to a man's brain. I did run to the store to grab a M8x1.25 Helicoil Kit but I'll first try to run the tap through to see what that can do. Thanks for the suggestions. I'll be glad to get the new manifold bolted up soon.

And just for documentation purposes for the next person that comes along with the exact same issue, definitely pick up some Cobalt drill bits to get through the stuck bolt. I had some DeWalt titanium bits that I tried with first and they barely made a dent.

 

Haha, any redundant task like that sure can get disorienting. I'll be glad to see it all bolted up! Thanks for the tip on cobalt drill bits, too.

This is also a super helpful tool for drill bit maintenance: https://amzn.to/3phVtug (drill doctor)

 

I think you are on the correct path. Drill and tap first, if that does not work, then and only then go the Helicoil route.

 

Is that flush with the head/block surface? Or is it slightly raised?

Either way I'd start by welding a nut to the bolt left in the hole...

 

Wanted to close out this thread by sharing my adventure from a few weeks ago. I bought an M8 Helicoil set just in case I would end up needing it. Cleaned the hole out again and proceeded to tap the hole. Seemed to be going fine until it got stuck about half way down. Also worth mentioning that I had no prior experience with taps outside of YouTube videos or knowledge of STI taps vs other standard size taps. Because the Helicoil is an STI tap, I did not have a tap wrench that would fit so I used a basic ratchet (spoiler: not a great idea) with a larger bolt extractor (another spoiler: really not a great idea) to grip the tap. When it got stuck half way through, I attempted to adjust the tightness of the extractor only to accidentally snap the tap off in the hole. Never been more mad at myself before that day. Here's what I was looking at:

Picture above was after I went at it with some needle nose pliers and my Cobalt drill bit that did ABSOLUTELY NOTHING on that hardened steel tap. Read up a bit on what my options were, only to be in worse shape after understanding what most people deal with after breaking off a tap. I decided to try my luck with a that I found on Amazon for $27 even though the reviews on these tap extractors were all over the place. I think I was lucky because the tap wasn't stuck deep in a hole and I was able to move it about 1/4 turn back and forth with the pliers a bunch of times because after 5-10 minutes wiggling the tap with the extractor tool, I got it to back right out.


Was honestly terrified at the thought of having to repeat this process but went back to Advance Auto and grabbed an M10 tap kit and got back to work on this final bolt, Went much slower this time, made sure to use lots of oil on the tap, and backed it all the way out and cleaned the hole numerous times before adding the replacement threads with some high-temp loctite. In the end, the M10 bolt seemed to screw in and hold just fine and I was able to get everything installed again.

Moral here is 1) don't be an idiot and get the proper tap wrench tool before starting and 2) don't jerk the tap in any way if it's stuck in the hole. For as strong as that steel is, it seems pretty brittle if you twist enough and then snap it in a certain direction. Hope nobody has to go through that, especially way back on the manifold bolt up against the firewall, but if you do, check out the Walton tap extractor. Just make sure you get the right size and the correct amount of flutes. Oh, and be prepared for some sore ribs from leaning over the body for hours and hours trying to reach back there.

I know this will help somebody down the road when they are freaking out like me and searching through the Hummer forums looking for someone who had the right solution.

 

Always use a bottoming tap in a blind hole!

 

Lisle Tap Socket Set 70500, they work great and fit in more places on a stubby ratchet that traditional T Handle Tap Wrench.

Think of it as tuition, you learned a bunch during your repair. KUDOS!