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Go Back   TDIClub Forums > TDI Model Specific Discussions Areas > VW MKIV-A4 TDIs (VE and PD)

VW MKIV-A4 TDIs (VE and PD) This is a general discussion about A4/MkIV Jetta (99.5-~2005), Golf(99.5-2006), and New Beetle(98-2006). Both VE and PD engines are covered here.

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Old June 3rd, 2020, 06:36   #1
Bhavick
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Join Date: Jun 2018
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Default Tap & Die Set for a Cross Threaded Hole

Hi,

To cut a long story short I've managed to cross thread one of the holes on my EGR valve. You know the EGR pipe that connects up to the EGR valve from the bottom via two 6mm Bolts. One of those holes I've cross threaded on the EGR and I've managed to get the bolt in but it isn't straight and it's beginning to annoy me. Please don't ask how i managed to do that but i did. Someone recommended using a tap and die set. I've never heard of it before and i was wondering if anyone knows anything about it and how it works?

Thanks
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Old June 3rd, 2020, 07:08   #2
KLXD
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A tap cuts threads in a plain hole. If you run it into the hole you've buggered it might follow the threads you've made with the crooked bolt and do no good as well as remove too much material and end up with a stripped thread.

If you manage to get it straight, maybe by leaving the EGR valve in place to use as a guide to get the tap straight, you might not follow the original threads and end up removing them. Even if it follows the original threads you'll be removing the displaced material from the cross threading and may end up with insufficient material to take the torque.

At that point you'll be putting in an insert but if you can't get a bolt in straight can you drill and tap a the new hole straight?

Might be better off leaving it alone or trying to get the bolt back straight. Get it lined up and tap it with a hammer to restart it correctly. Even then it might strip.
__________________
Saying no to gas for 25 years:

Current: 02 Jetta, Auto; 98 Jetta, 5 Spd; 98 Dodge, 5 Spd, SB, 4x4; 84 Grand Wagoneer with Nissan SD33T, NV4500, Dana 300, Reverse Cut Dana 44, Dana 60

The Black Sheep (Only gasser): 85 CJ, 4.2 w/4.0 Head and Mopar FI.

Past: 85 Mitsubishi PU, 4D55T; 81 Rabbit, 1.6; 80 Dasher, 1.5; 79 Rabbit, 1.5
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Old June 3rd, 2020, 07:16   #3
Bhavick
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Quote:
Originally Posted by KLXD View Post
A tap cuts threads in a plain hole. If you run it into the hole you've buggered it might follow the threads you've made with the crooked bolt and do no good as well as remove too much material and end up with a stripped thread.

If you manage to get it straight, maybe by leaving the EGR valve in place to use as a guide to get the tap straight, you might not follow the original threads and end up removing them. Even if it follows the original threads you'll be removing the displaced material from the cross threading and may end up with insufficient material to take the torque.

At that point you'll be putting in an insert but if you can't get a bolt in straight can you drill and tap a the new hole straight?

Might be better off leaving it alone or trying to get the bolt back straight. Get it lined up and tap it with a hammer to restart it correctly. Even then it might strip.
God after reading your reply i don't feel very confident anymore lol. I thought i was onto a possible solution to.
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Old June 3rd, 2020, 08:47   #4
PakProtector
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For this sort of thing, feel gotten from experience is a very useful thing. So it a tap with a very gentle lead in taper so it can be surer of lining up with good threads and not wrecking any good ones. It is something that can be further wrecked easily, so I'll not lie to you about that possibility.
cheers,
Douglas
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Old June 3rd, 2020, 08:54   #5
BobnOH
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Tap and die sets are for cutting new threads. They make a thing called a thread chaser to clean up mildly damaged threads. But if your bolt is actually crooked, you're beyond that. Get a thread repair kit like heli-coil or timeSert.
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Old June 3rd, 2020, 10:55   #6
KrashDH
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Were you able to back your cross threaded bolt out of the hole in the same orientation you threaded it in? If so:

Aluminum is soft. If you've cross threaded the hole, generally you can get a tap to start straight in aluminum. If you can get your tap to start straight in the hole, it will "jump" the cross threads back into the original threads and just cut through the cross thread material. If you can get it to do that, then you'll be ok.

If you cross threaded the hole and then ripped the threads out, then this method won't work
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Old June 3rd, 2020, 17:37   #7
KLXD
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There's also a thing called a back tap. It closes down so you can insert it to the bottom of a hole then expands to pick up the original threads and cuts on the way out.

Obviously the hole has to be deep enough to use it and you have to be able to find one.
__________________
Saying no to gas for 25 years:

Current: 02 Jetta, Auto; 98 Jetta, 5 Spd; 98 Dodge, 5 Spd, SB, 4x4; 84 Grand Wagoneer with Nissan SD33T, NV4500, Dana 300, Reverse Cut Dana 44, Dana 60

The Black Sheep (Only gasser): 85 CJ, 4.2 w/4.0 Head and Mopar FI.

Past: 85 Mitsubishi PU, 4D55T; 81 Rabbit, 1.6; 80 Dasher, 1.5; 79 Rabbit, 1.5
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Old June 4th, 2020, 07:06   #8
KrashDH
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Quote:
Originally Posted by KLXD View Post
There's also a thing called a back tap. It closes down so you can insert it to the bottom of a hole then expands to pick up the original threads and cuts on the way out.

Obviously the hole has to be deep enough to use it and you have to be able to find one.
This is pretty interesting. I worked as a machinist for 5 years and never saw one of these. Had to go look it up because of your post, pretty cool bit of simple engineering!
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Old June 5th, 2020, 17:50   #9
rwthomas1
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Go get a bolt of the same size and thread pitch, but at least 3inches in length. Line up the new long bolt to the crossthreaded hole, the length will make it very easy to see if it is straight. Turn it gently with finger pressure. If you can get it to start straight, then turn it gently with tools. Gently. If it goes in two or three turns, while staying straight, stop. The length of the bolt will also allow you to hold it straight as it is turned in. Keep it on track. If you get the 2-3 turns, back it out and put a little light oil on the threads and do it again. Keep slowly turning it in and backing off. What you are doing is forcing the metal back to where it belongs. If this takes lots of pressure, you're doing it wrong. You have little to lose at this point, so try this, or run a tap through it and pray there is enough meat for the fastener to hold.
RT
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