Re-tapping the exhaust threads

[Doat]

Alright I asked this question in a couple of other threads but I was not 100% sure on this because I did not remember what size drill bit I used, so the answers to ME were not reassuring. However, I remembered asking about this in my old head gasket replacement thread when I first bought my MK3 and I went through and searched and found out what size drill bit I used, 13/32, and I used the oem exhaust studs with the correct size helicoil. Now I have the DM 7/16 kit and my question is with this kit do I remove the old helicoil and use the 7/16 coarse tap to re-tap the threads or do I use that 7/16 drill bit, then tap, and insert the new coils as I did before with the 13/32 size? I assume taping a hole with threads in it is not a good idea.


I do apologize if some of you who respond here have answered this question but like I said I was not 100% sure because my mind was going nuts with the size drill bit I used and all of that, so now that I know what size I used I can be reassured.

 

[suprarx7nut]

Something doesn't sound right here. The DM kit needs a 29/64 drill bit for the 7/16 inserts.

If you used a 13/32 bit on the existing installation you won't have much material to work with going to a 29/64 bit.

Not to mention a 13/32 looks like the size used for an M10x1.5 insert and the DM kit (7/16) is an inch thread measurement. The threads won't line up. This means you would want to make sure the 29/64 bit would completely remove the threads from your existing helicoil. I'm not sure the 29/64 drill bit would remove all the material carved by the tap you used to insert the existing helicoils.

I wouldn't try to do the 7/16 if you already have M10 inserts in there.

 

[Doat]

I was looking at the drill bit in the 7/16 kit and it seems pretty large looks like it would widen the hole if anything but I am going off of memory at this point. I think I only have one loose exhaust stud because when I was putting my exhaust side back together there was one stud that would tighten then if I kept turning it by hand it would eventually tighten up then break loose and repeat. Maybe I just need to clean out the helicoil or replace it but I was still able to torque it to 30ft lbs no problem.

 

[Dirgle]

The DM kit comes with a 29/64th drill bit, necessary for the tap and 7/16th helicoils.

SO
-->Drill 29/64th--->Tap 819-7--->helicoil.

Now that said, there are some concerns over the DM course stud kit. Since my engine was out when I did mine I went this route so I could use the OEM studs. It's a little over kill but very reliable.
http://www.amazon.com/Thinwall-Keylocking-Threaded-Inserts-Steel/dp/B002GPLC1S

 

[Doat]

Well the DM kit comes with everything I need it has the studs and nuts, etc. even the cutting and anti seize fluids which I am sure you guys know. I am not worried about re-using the studs I have I would rather go with the new stuff in the DM kit to be honest. I want to know if I can use this kit even though I helicoiled my head already with a 13/32 drill bit with the 29/64 and fix my exhaust leak unless my math is incorrect, which would not be impossible lol, I think the DM kit's drill bit is a little bit larger than the one I used before.

 

[suprarx7nut]

Ok a couple things:

1. The 29/64 drill bit is larger than your old one, however, that's not the concern. The drill bit would need to be larger than the outer diameter of the tap/helicoil you used (assumed to be M10). I'm not confident it would be. If the drill bit cannot fully clean out your existing threads you will get poor engagement (grip) out of the larger helicoils. You could make it much worse than it is now.

2. If you got your studs to torque to 30 ft-lbs I'd leave them alone. There's no need to helicoil more as a preventative measure. If you got to 30 ft-lbs move on to something else.

 

[Doat]

Very good point but the fact that the stud broke loose and then re-tightened when I tighten it by HAND really bugs me lol. Maybe I will get a boost leak check done and feel around the manifold and downpipe area to see if it's actually leaking there but according to how my old manifold gasket looked there is a leak right under the CPS area on the manifold because that last part was blackened it was like the last 2 exhaust holes or ports whatever.