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Unread 10-20-2014, 02:31 AM   #1
MrRaider
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question about rethreading a bolt

The bolt size is a 1/4 for the oil pan. What size bit do I need? I'm not 100% sure but do a #7 drill bit seem right?

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Unread 10-20-2014, 05:56 AM   #2
Myjeep1986
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Tap/die

If you are wanting to thread the hole to match the bolt, you should buy a tap for the 1/4 x 20 pitch at a reputable home repair depot or hardware store and buy the drill bit recommended on the back of the package the tap came in.
Start with a 1/8 inch bit and then move to the correct size for the tap.
If you are trying to use an existing hole, you may need to go up one size to be sure there is enough "metal" to tread;
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Unread 10-20-2014, 06:36 AM   #3
EABiker
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My tap chart does call out a #7 drill for a 1/4-20 bolt.
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Unread 10-20-2014, 08:53 AM   #4
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Quote:
Originally Posted by EABiker View Post
My tap chart does call out a #7 drill for a 1/4-20 bolt.
x2, #7 for 1/4-20, #3 for 1/4-28.
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Unread 10-20-2014, 09:02 AM   #5
Old4X
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You can not re-tap a damaged threaded hole for the original size bolt, it is oversized from the damage.

The proper repair is to install a helicoil. If it is 1/4 X 20, get that size repair kit. It will come with the proper bit, helicoil inserts that accept 1/4 X 20 bolts, and an installation tool.

If you just run a 14 X 20 tap into a damaged hole, the bolt will pull out before proper torque is reached upon installation of the pan.
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Unread 10-20-2014, 10:07 AM   #6
tom_sprecher
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"Rethreading" or chasing threads on a bolt requires a die and there is no drill involved.
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Unread 10-20-2014, 10:18 AM   #7
Old4X
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Quote:
Originally Posted by tom_sprecher View Post
"Rethreading" or chasing threads on a bolt requires a die and there is no drill involved.
Or a "thread file". I have one I use occasionally for cap screws with small areas of crushed thread.
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Unread 10-20-2014, 12:37 PM   #8
jbolty
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This is a little off track.

I would guess the problem is an oil pan bolt broken off in the hole and the OP wants to drill it out and re tap the hole. The other option is a stripped hole in the block but that's pretty unlikely with a 1/4 bolt.

If it's the first option I would start with trying a left hand drill bit.
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Unread 10-20-2014, 12:43 PM   #9
Old4X
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Quote:
Originally Posted by jbolty View Post
This is a little off track.

I would guess the problem is an oil pan bolt broken off in the hole and the OP wants to drill it out and re tap the hole. The other option is a stripped hole in the block but that's pretty unlikely with a 1/4 bolt.

If it's the first option I would start with trying a left hand drill bit.
If that is the case, yes , left handed bits come in handy.

But, whatever he does, he doesn't want to break an EZ-out off in the hole.
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