So one of my holes that hold my derby cover in place is stripped. I tried re-tapping the hole and doing some silicone on the threads still not grabbing. It is the bolt at the 7 o'clock position so a little worried about riding with it. Looks like a helicoil is a good option to repair the problem. My question is how far to drill the hole out. (Depth) I assume to deep will cause a big problem. Thanks.
Ozzy

 

Also when you break the tang off the coil how to you guys get it back out of the hole, or do you just leave it in? Thanks

 

http://www.nwlink.com/~kbaker/Automo...oil_12_04.html

 

One more question I hope. The thread that is in the hole now is a 1/4 20. Is that the helicoil kit I need to order to fit the bolt? Thanks

 

If you were just drilling a hole to tap a 1/4 x 20 thread in a hunk of metal, you would use a #7 or 13/64 (.2010") bit.

For a 1/4 x 20 helicoil, the recommended drill bit (by helicoil) is a 17/64 (.2570) bit.

So you ask for a 1/4 x 20 helicoil kit and pick up a 17/64 drill bit.

http://www.lincolnmachine.com/tap_drill_chart.html

What are you rethreading/repairing? Helicoil is not the only option. YD

 

I have a stripped hole at the 7 o'clock position on my derby cover. Tried retreading the hole already to no avail.

 

Heli coil will work fine for that. Plenty of threads posted on the same problem. Just take your time and go slow. make sure you drill and tap nice and straight.

Places like Orielly and autozone sell the helicoil or similar brand kits. If done right, it will function as it did new.

I know my dodge diesel cummins engine came from the factory with helicoils installed on certain intake fasteners and no issues. YD

 

Helicoils are designed for new build, not repairs, although they do get used for that. Any aircraft engine will have umpteen of them - dozens of helicoils flying in loose formation!

 

Measure the depth of the hole and buy an insert that is about 1/2 to 2/3 of the hole.

Drill to the existing depth, then counter sink hole to about 5/16 dia. with a 120 Deg. countersink.

Install the insert 3/4 to 1 1/2 turn from the top of hole.

Break the tang and remove.Remove it with small tweezers or holding a air nozzle 90 deg to the hole will remove it.

 

Time-sert ( http://www.timesert.com/ ) is a viable option and is ( usually ) easier for a novice than a Heli-Coil