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Discussion Starter #1
OK as most of you know this job sucks.

My rear most exhaust manifold stud (passenger side) had snapped clean off about 1/8" below the surface of the head. That was the easy part, it came out really easy with an extractor.

The problem I'm having right now is that the bottom front most stud hole just started to cross thread putting a new stud back in. I think it happened as this was the last stud out and I has struggling to hold up the manifold while backing the old stud out. Looks like I have 2 messed up threads, rest are good.

Will I be able to chase this with a M8 x 1.25 tapered tap?

My dilemma is if I screw it up further it will have to be drilled out and heli coiled. But, there isnt enough room to get a drill in there...

Opinions? This one is making me nervous.
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@trev Sorry to hear about that.

I had a similar problem a few years back where the tip of a Balancer Puller snap inside the snout into my crank, and I have limited room to drill and extract it.

I bought a 90* Air Drill that I was able to drill into the "snout". That was the only way I could get a drill onto it due to space.


Here is a link to a similar air drill. It is the most compact, and lightest drill I could find at the time. Drill speed controlled by air.

Pity you aren't closer, I could loan you mine to get through this.

Maybe you can just "rent it" for a day or two?
 

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You have no choice but to try and chase the threads with a tap. Use a good amount of oil, try to get it on straight. If it cross threads, I would probably just tap a larger stud there. I think there's room on the manifolds for a fatter stud.
 

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What are you talking about? I can't wait to dive back in and take my manifolds out again.

I don't really know the answer. Does the tap thread in easily enough or are you fighting with the mangled threads to even get it lined up. I just wouldnt want you to misalign the tap and make a whole new set of threads.
 
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The tap should be slightly tapered so it goes in pretty far before it starts cutting metal. Get er dun! (And post photos!)
 
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Discussion Starter #8
I guess this would be a good excuse to get a new power tool. Even at that I don't know if I would be able to get a right angle drill in there... it's just the most awkward spot and space is super limited. Luckily I was able to unbolt the AC compressor to make a bit more room.

The tap I have is tapered. I had it just sitting in the hole for the picture.

I have done a few taps and heli coils in the past but never tried chasing with a tap to fix threads. My fear is the threads on the tap won't line up with the good threads in behind and fudge it up more. If I can't get a drill in after as a last measure, I think the head will have to come out.
 

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The tap should be slightly tapered so it goes in pretty far before it starts cutting metal. Get er dun! (And post photos!)
I'm guessing you can get different taps, some with more taper, others with less?

From the photo, it does appear that he stopped BEFORE he damaged beyond just the first couple of rounds. So yea, as you suggest, I'd start with a fairly tapered tap in order to get a considerable portion of it in the whole, perhaps aiding in getting it perfectly aligned. And then if you are fortunate, you won't be altering the undamaged threads at all.

But, if it does appear that the tap even slightly alters the undamaged threads, then you might need a tap that has very little taper so you can finish the tapping all the way down to the bottom, since the tapered tap might not.

Although I might be wrong about all of this since the head is aluminum, maybe the new stud itself will sufficiently dress the undamaged threads if tapping results in a minor change in thread alignment?



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Right angled air drills are far far smaller than electric.

I think you will be allright, you will know if the tap is going in straight by how easy it goes. It's soft aluminum it should be fairly easy to chase.
 

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Just don’t use a bottoming tap with very little taper. A normal tap should work fine. Go slowly and carefully.
 

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Tap the bolt lightly and turn, tap the bolt lightly and turn, tap the bolt lightly and turn, tap the bolt lightly and turn. Has proven amazing results on many an oil rig, haha.
 

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I would make a simple busing to keep the tap aligned
Use a taper tap if you can

Looks like you dodged a bullet !

-Brian


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You should be fine with the tapered tap. the idea is that it can get in far enough with the taper to "follow" the threads you already have. Just go slow and go in half a turn and then back out a quarter turn. Once you have a full turn on the tap, back it right out and see if it looks like you are gonna line up.

Good luck, that's not a fun job!
 
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