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Discussion Starter #1
I was installing a new differential cover, and I think I stripped one of the bolt holes on the differential housing. I did some research and need to insert a 5/16"-18 Helicoil, which requires drilling the hole using a 21/64" drill bit. My concern is that I only have a hand-held drill, not a drill press. What can I use or fabricate to ensure my hand-held drill stays centered while I drill the hole? Any ideas?
 

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Start with the smallest drill bit that will not fit into the stripped hole and work your way up. Just be sure to hold the drill and bit square and straight when drilling. With the smaller bit it should help drill-slide into the stripped hole easier. Also very important when tapping is to keep the tap square also. I have put in a few heli-coils this way.
 

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Most drill bits (not all, though) have a tapered tip. That taper wants to center the bit in an existing hole. You can do as suggested by Moodyalaskan, that isn't bad advice. But the reality is the new hole isn't going to be much bigger than the old hole, and as long as you have a drill bit that has the standard tapered point it will want to center. From there all you need to do is make sure you drill in straight. But unless you really get way out on that it will likely be good enough. I have done a number of re-threads using a hand drill. It isn't that bad. Just take your time and make sure you drill as straight as you can.

That said, there is the Heli-Coil option and there is something called a Time Sert. The Time Sert is a better option, it is actually a one piece threaded insert instead of a coiled insert like a Heli-Coil. Pretty much the same process to install, but a better more durable end result.
 

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You're not taking a lot of metal away, if you think about it 5/16 is 20/64 so your only removing 1/64 of metal and that's really just enough to tap it with the helicoil tap so you can put the coil in. I've used them a lot on motorcycles and they're pretty easy to use.
 

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If you have a couple days to spare, you can get a tool to make your hand drill into a drill press:

 

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Drill bits just don't work well when the center point isn't supported. Reamers work better for enlarging holes.
 

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Drill bits just don't work well when the center point isn't supported. Reamers work better for enlarging holes.
I have done a number of these, as long as your drill bit is a standard tapered point drill bit and not one of those pilot point drill bits it will work just fine. The new drill bit is only about the size of the threads you are replacing, so there is very little metal removal and the bit will want to go straight into the threaded hole.
 

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If you have a couple days to spare, you can get a tool to make your hand drill into a drill press:

I used to have a similar device (made by someone else). In fact, it might still be hanging around in the garage somewhere. I haven't used it since I got a floor mount drill press, but it actually worked OK for what it was. It does take up a fair bit of space, and doesn't work very well in tight quarters, but does have some specific uses for which it is great.
 

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Discussion Starter #9
I found this:

I wonder if that would actually work for this job? No, I'm not going to buy it, but was just curious if it would hold enough to the differential housing to work. Pretty cool tool.
 

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I found this:

I wonder if that would actually work for this job? No, I'm not going to buy it, but was just curious if it would hold enough to the differential housing to work. Pretty cool tool.
I don't think it would be easy to use. Even if the magnet is super strong, good luck finding a large flat and level place where it actually fits to put it, around the diff or hardly anywhere on the Jeep for that matter.

As for drilling and tapping, in my limited experience just doing the best you can to keep everything straight gets you close enough to get a functioning bolt for clamping something down. Your angle may end up being off by a degree or so, making your bolt head not perfectly flat to the diff cover, but it'll still apply the pressure you need and work just fine unless you get way off, IMO. I used a helicoil after stripping a thread in my transmission crossmember when getting hasty installing my Rock Hard engine/trans skid, it was easy and worked well. Though that timesert posted up thread looks nice.
 

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just tap the one hole that is stripped the next size up meteric bolt. Ie I think stock is 5/16" bolt so tape it for an 8mm bolt. should not have to do anything other than run the 8mm tap in. should be just about perfect unless you really stripped the hole out. just remember when you pull the cover off again you have one meteric bolt and remember which hole it goes in.
 
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