Stripped exhaust bolt, very messy attempt

[tbrand69]

If you have already drilled it out "too big", it's the PERFECT time to install Heli-Coils.

Get the kit for the M8 x 1.25 threads, it has a special bit (or tells you what bit to use) and will also have the special tap to use. Install your coils and you are good to go.

Note: do not use that tap for ANYTHING else, the ONLY thing it is good for is installing M8 x 1.25 Heli-Coils.

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Perfect. I measured the depth of the other screw holes to about 25mm. I assume I should drill this guy out to the same depth?

Tommy

[Steve]

I would not go any deeper than the existing holes. You do not want to drill them all to match that one, they might not have the room behind them before getting into something that should not have an extra hole in it.

If you are going to install Heli-Coils in other holes, measure the depth of the hole, drill it larger, but not deeper, tap it, install the coil, move on to the next hole.

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[tbrand69]

I would not go any deeper than the existing holes. You do not want to drill them all to match that one, they might not have the room behind them before getting into something that should not have an extra hole in it.

If you are going to install Heli-Coils in other holes, measure the depth of the hole, drill it larger, but not deeper, tap it, install the coil, move on to the next hole.

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Oh no no no, just the one hole lol. I see no reason to install the coils in the other holes. They are perfectly fine and good to go. I will probably install studs on them at some point, though.

[tbrand69]

I would not go any deeper than the existing holes. You do not want to drill them all to match that one, they might not have the room behind them before getting into something that should not have an extra hole in it.

If you are going to install Heli-Coils in other holes, measure the depth of the hole, drill it larger, but not deeper, tap it, install the coil, move on to the next hole.

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Actually I had a question. Upon further research, it says the M8 coil requires a 1/4 inch bit and hole. I have started drilling the hole with a 5/16 bit, so it's 1/16 larger. Common sense tells me that this will be a problem when trying to install the coil.

The hole should be about 25mm deep, and I have only drilled down to about 5mm. I could conceivably drill the remaining 20mm with the correct 1/4 inch bit. My question is: would it be okay to have the new coil threads starting 5mm below the surface of the hole? As a result, there would be a 5mm gap where there are no threads. Would that severely compromise the strength of the mount?

Tommy

[Steve]

Actually I had a question. Upon further research, it says the M8 coil requires a 1/4 inch bit and hole. I have started drilling the hole with a 5/16 bit, so it's 1/16 larger. Common sense tells me that this will be a problem when trying to install the coil.

I am not near my helicoil set to verify, the 1/4" bit seems a bit small, bit might actually be correct.

The hole should be about 25mm deep, and I have only drilled down to about 5mm.

What makes you think the hole needs to be that deep? How deep is the original hole?
I would not go any deeper than that, there are oil passages and whatnot lurking just below the surface.

My question is: would it be okay to have the new coil threads starting 5mm below the surface of the hole? As a result, there would be a 5mm gap where there are no threads. Would that severely compromise the strength of the mount?

See my previous comment, I think the only thing that will compromise your strength will be drilling into a void.

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[tbrand69]

I am not near my helicoil set to verify, the 1/4" bit seems a bit small, bit might actually be correct.



What makes you think the hole needs to be that deep? How deep is the orignial hole?
I would not go any deeper than that, there are oil passages and whatnot lurking just below the surface.
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I measured the depth of the other exhaust holes. They are 25mm deep. I agree, any deeper could pose a serious risk.

See my previous comment, I think the only thing that will compromise your strength will be drilling into a void.

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So it would be okay if the coil is only attached to the 20 +/- threads with a small gap just below the surface of the opening?

Tommy