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how to repair crossed threads


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10 replies to this topic

#1 shortskoolbus

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Posted 21 May 2009 - 12:53 PM

Hey guys I need some help.

I cross threaded one of the tabs on my torque converter the last time I put my tranny back on. Because it wasn’t in a position where I could tape it out and put a helicoil in (without pulling the tranny again) I had to just run a M8 x 1.25 tap right through it which I think just chopped off the top of the peaks of each thread.. Now I have the tranny out again I want to fix that hole.

I’ve never done this before, but I think its just a matter of tapping the hole out to the bigger size and then threading the helicoil in. Do I need to drill out the hole at all or can I just start tapping with the larger tap since there are still threads there.

Do I just use a tap one size up?

Edited by shortskoolbus, 21 May 2009 - 12:59 PM.


#2 OB99W

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Posted 21 May 2009 - 01:51 PM

[...]Do I need to drill out the hole at all or can I just start tapping with the larger tap since there are still threads there.[...]

There are specifications for hole size versus tap size that should be followed. It's very risky to use a tap on any hole that's undersized -- the tap can jam, sometimes ruining the threads or even breaking in the process of freeing it. As a general rule, the correct size hole, correct lubrication (varies with material being tapped), and frequently backing out the tap to clear chips tends to lead to a successful job.

As to a HeliCoil, I'd suggest relying on their specific instructions.

#3 OB99W

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Posted 21 May 2009 - 01:56 PM

Not that I think Wikipedia is the final authority on anything, but this article has some useful info: http://en.wikipedia....iki/Tap_and_die

#4 CNY_Dave

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Posted 21 May 2009 - 02:51 PM

A drill, tap, and insertion tool come with the helicoil kit.

I've heard a timesert is stronger and better, but a helicoil is usually stronger than the original threads and fine for almost any repair.

Dave

#5 shortskoolbus

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Posted 21 May 2009 - 03:04 PM

just picked the helicoil kit

didnt come with a tap handle or drill bit, but looks pretty straight forward.

#6 mva5142

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Posted 21 May 2009 - 03:39 PM

I did a couple heli-coils for the first time two weeks ago.

Pretty straight forward. Use the drill bit size called for, drill out the hole, tap it with the tap, screw the helicoil in and use the little tool to break of the tab end so the screw can go all the way through if need be and you are ready to tighten it back up.

You can search youtube under helicoil and see a couple demonstrations on how it works. Really explains it better than the crappy directions on the helicoil box and shows how easy it is.

Matt

#7 jinshiyang

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Posted 22 May 2009 - 10:43 AM

Really explains it better than the crappy directions on the helicoil box and shows how easy it is thread insert helicoil

#8 grossgary

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Posted 22 May 2009 - 11:57 AM

yeah it's fairly straight forward and a torque converter should be really simple.

drill, tap, and insert. don't just use the tap, make sure you drill the appropriate size hole first. the helicoil tool will have the appropriate size drill bit printed on the shaft.

#9 shortskoolbus

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Posted 22 May 2009 - 12:00 PM

so i tried to drill the hole, my drill is too wimpy.


i ended up not doing it.. :-\, but the threads that were there seem okay still, i just used plenty of loctite.

#10 Gloyale

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Posted 23 May 2009 - 10:04 AM

I think a helicoil may not work here, because the hole is a straight through, there is nothing for the helicoil to bottom against. My guess is that even if the insert installs correct, it will want to simply thread it's way out the back of the tab as the bolt is threaded in.

I think you would be fine to simply tap out the hole to the next standard size. Probably 3/8ths. Cheaper easier, and arguably more reliable than a helicoil.

Whatever you do, make sure you've got a good repair. All the torque of your engine is transmitted to the tranny through those four small bolts. One of them being loose, or not clamping right could cause some issues.

Most notably alot of noise from the plate flexing and buckling. Also having a bolt pop out and rattle around loose in there would be very bad.

#11 johnceggleston

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Posted 23 May 2009 - 10:47 AM

perhaps clean up the threads with the current size tap and a new bolt.




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