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Tapping 8mm x 1.25 help

Cal6969

Plastic
Joined
Sep 30, 2023
I bought this

BILITOOLS M8x1.25 Thread Repair Kit​

everything went right. drilled in an aluminum hole. tapped the helicoil in. everything went smooth untill I start to screw the bolt in which is a

M8-1.25 x 50mm Socket Head Cap Screws​

I'm not even half way in and its start to tighten where I feel it should be tightening at all...so I backed off and looked at the screw and you can see the thread messed up. tried my best cleaning it too. this is the 2nd helicoil that
I removed cause it did it twice already. I can't think of anything else to solve this problem.
 
I bought this

BILITOOLS M8x1.25 Thread Repair Kit​

everything went right. drilled in an aluminum hole. tapped the helicoil in. everything went smooth untill I start to screw the bolt in which is a

M8-1.25 x 50mm Socket Head Cap Screws​

I'm not even half way in and its start to tighten where I feel it should be tightening at all...so I backed off and looked at the screw and you can see the thread messed up. tried my best cleaning it too. this is the 2nd helicoil that
I removed cause it did it twice already. I can't think of anything else to solve this problem.
It is unclear what size drill you used to enlarge the original (stripped?) hole. It is unclear if you used an M8x1.25 STI tap to cut oversize threads in your drilled hole. One way to interpret your statement is that you tapped (hammered) a Helicoil into your drilled hole without using the STI tap.

Try again.

If you followed the kit directions correctly, maybe the issue is that you bought a repair kit for $14.99 that would cost much more if made by a quality tool company. (Do not use an adjustable Crescent-style wrench to drive a tap like the guy in the video).

Larry
 
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Original hole was a 6mm but I bought it stripped (leaking diesel injector) drilled it with supplied drill bit. Don't see no video but I did use a 7 mm rachet....back and forth removing anything off the tap. I was extra carefull. you really thik it can cause a problem? I think you're right and hopefully you are. The kit is non STI tap. So I'm going to order one off amazon. If things work out ill come back with some images
 
But you bought a "kit". Unless you have genuine helicoils (or exact equivalent) and STI alone wont help. STI <> coil is a matched set.

I hate helicoils... went to Timeserts a long time ago and never looked back.
 
wow, I came back just to ask that question but you answered it. so I looked into a STI kit and looking at the drill bit they are using, looks like the same size which is a 8.3
I actually canceled that kit and bought one thats better quality, without the drill bit and case. cause i'm buying the same size drill bit but also better quality and size 8.3...

ill look into Timeserts
 
maybe it is a STI? It also comes with a small allen wrench which I didn't use but I've read some comments on YT correcting a video using the allen wrentch but didn't quite get what he was saying....
 
As Mr Vanice says "No mention of tapping the 'new' hole" ......this maybe the missing link .......Otherwise ,Its quite impossible to go wrong with any kind of recoil system if the instructions are followed.....from the cheapest to the gold plated .
 
STI and helicoil are the same thing, helicoil is a brand, STI is a generic term.

If you drilled it with the supplied drill, tapped it with the supplied tap, and installed the supplied insert, you have a different problem. Either the insert skipped a thread when you installed it, which happens if you aren't careful, or you pulled the last turn of the insert out of the thread when you broke the tang off, which also happens if you aren't careful, or if neither of those things, maybe your screw isn't actually an M8x1.25. Check the screw against the tap, the pitch of the threads should align perfectly.
 
Cal, as evidenced by several of the posts above, you need to take a deep breath, and then write out exactly what you did, and what tools you used for each operation.

Use proper sentences also, please.

I've never heard of an allen wrench being used to install a STI.
 
Next, check and be sure you have tapped the STI thread deep enough to let the thread insert screw all the way in without kicking out a "tail" at the bottom. This will do exactly what you describe if the STI thread is not deep enough.
 
To add a bit to this, the tap supplied with the kit has or at least should have a tapered section at it's tip. This tapered section does not cut a full thread so a heli-coil or STI screwed into that section will be compressed to a smaller diameter than the stated size (8 mm). That would cause the M8 thread to jam in it.

You must tap the hole deep enough so that there are FULLY CUT threads for at least as deep as the insert is long. In other words, after the tapered section of the tap is completely inside the hole, you must continue tapping for as many turns as the insert has and preferably one more.

In many cases this can require a deeper hole than the original bolt used. Perhaps as much as twice as deep.



Next, check and be sure you have tapped the STI thread deep enough to let the thread insert screw all the way in without kicking out a "tail" at the bottom. This will do exactly what you describe if the STI thread is not deep enough.
 
To add a bit to this, the tap supplied with the kit has or at least should have a tapered section at it's tip. This tapered section does not cut a full thread so a heli-coil or STI screwed into that section will be compressed to a smaller diameter than the stated size (8 mm). That would cause the M8 thread to jam in it.

You must tap the hole deep enough so that there are FULLY CUT threads for at least as deep as the insert is long. In other words, after the tapered section of the tap is completely inside the hole, you must continue tapping for as many turns as the insert has and preferably one more.

In many cases this can require a deeper hole than the original bolt used. Perhaps as much as twice as deep.

Right, I didn't think all the detail needed to be added, but exactly... And if you find that you did in fact do this and can't easily get the helicoil back out so you can tap the STI deeper, there's usually an easy fix for that, too. Run your M8 (or whatever matches the insert ID thread) tap through the hole containing the helicoil. It will almost always cut off any of the helicoil "tail" that's sticking out in the way, solving the problem.
 
No matter how many times we've done something, somebody else always comes up with another gem for the mental toolbox. Those were two good tips.
 








 
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