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Drain Plug snapped. Extracted it and helicoil came out
Hi.
As the title states, I had a rather unfortunate discovery on my C7.
I've done the past few oil changes on the car myself with no issues and I tend to torque it with a torque wrench but set to 25ft-lb. At around 20ft-lb, the torque wrench started to spin super easy and unfortunately the drain plug broke. How unfortunate.
I spent an hour or two extracting the bolt as it was quite difficult but I was able to get it out. However, I noticed at the end of the thread there was this metal spiral hanging out. I just assumed it was from the broken bolt so I decided to pull it out and it was *not* a part of the drain bolt.
I discovered that the previous owner must've inserted had the pan retapped and placed a helicoil in there to retain the OEM M12x1.75 sizing.
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Not really sure what my best options are here.
Should I try to place in a new m12x1.75 wire thread in the hole or try a M14x1.5 oversized drain plug.
This is on my built C7 Z51 with an A&A supercharger (side note, been over 30,000km since supercharger install and ZERO issues except this drain plug so).
They are helicoiled from the factory, have been since '97. 20yrs in LSs and you're the first I've heard of pulling the coil out however. Not a common problem at all
re-insert a new coil. Break tang, rinse tang out of oil pan. Done
Edit: you're also overtorquing the plug. 18ft lbs is the OE torque spec. Torque wrenches generally aren't considered accurate at the low and upper end of their scales, so if your wrench bottoms out at 25ft/lbs- you're really putting the beans on a small, ungraded bolt
based on the condition of the head of the bolt, it's been overtorqued a lot in the past too
Last edited by arthursc2; Jun 3, 2026 at 11:50 PM.
IDK what sort of facility you have so I am not sure if you can do a Helicoil properly but assuming you can, I would like to replace the drain bolt with a drain valve. That bolt looks like it hasn't been done with the right socket based on the picture with it in your hand. I see signs of HE-MAN being there.
They are helicoiled from the factory, have been since '97. 20yrs in LSs and you're the first I've heard of pulling the coil out however. Not a common problem at all
re-insert a new coil. Break tang, rinse tang out of oil pan. Done
Edit: you're also overtorquing the plug. 18ft lbs is the OE torque spec. Torque wrenches generally aren't considered accurate at the low and upper end of their scales, so if your wrench bottoms out at 25ft/lbs- you're really putting the beans on a small, ungraded bolt
based on the condition of the head of the bolt, it's been overtorqued a lot in the past too
Originally Posted by aklim
IDK what sort of facility you have so I am not sure if you can do a Helicoil properly but assuming you can, I would like to replace the drain bolt with a drain valve. That bolt looks like it hasn't been done with the right socket based on the picture with it in your hand. I see signs of HE-MAN being there.
Interesting about the factory coil. Did not know that.
Regarding the ft-lb, I made a mistake. I had it set to 25nm (Canadian sorry) on the torque wrench which is 18 ft-lb, just a mistake in the thread. But you are right about the bolt definitely being over torqued in the past. I know the mechanic shop I took it to that built it took the plug on and off multiple times and I don't believe they ever replaced it.
Would using this kit be sufficient to place the new threaded coil into the hole? I won't be using the taps or anything as I don't believe I need to tap the hole at all, just placing a new coil in.
Otherwise, I may attempt to do the oversized oil drain plug and if that does not work, it looks like my cheap repair will no longer be a cheap repair
Why would you need a torque wrench to snug up your drain plug. There isn't any pressure in the oil pan. A good washer, clean surface and gudntite is just fine. I have done hundreds and never had a leak.
Why would you need a torque wrench to snug up your drain plug. There isn't any pressure in the oil pan. A good washer, clean surface and gudntite is just fine. I have done hundreds and never had a leak.
You need to use a torque wrench to avoid applying too much torque!
(pic deleted) Would using this kit be sufficient to place the new threaded coil into the hole? I won't be using the taps or anything as I don't believe I need to tap the hole at all, just placing a new coil in.
Otherwise, I may attempt to do the oversized oil drain plug and if that does not work, it looks like my cheap repair will no longer be a cheap repair
That kit will be fine. If you need some help with "how to", I would be willing to help. This is a very simple repair, I know it seems daunting- but I've installed thousands of helicoils in my time as a machinist. I have a soda can full of broken tangs- there is nothing to this repair except your anxiety about it is ramping you up
Originally Posted by Tinkertech
I would chase the threads and clean them real good before installing a new Helicoil.
Just how do you expect to remove the 'break off' tab from the installed pan?
And I'd use a longer Helicoil.
Its called a tang, and you can rinse it out with oil. You can also put a glob of grease on the tool to capture the tang when you snap the tang off. This is a very simple repair. I would not chase threads unless the lead thread of the pan has been damaged. You don't want to open up the minor or major diameter as the wire needs to be an interference fit in the pan
Originally Posted by M61A1MECH
You may want to look into Timesert, actually a better repair than a helicoil. https://www.timesert.com/
Timesert is absolutely a better repair, but based on what I have seen in this thread, the skill level necessitates just reinserting a helicoil and snapping the tang off. And even that process seems to be flying over some heads
That kit will be fine. If you need some help with "how to", I would be willing to help. This is a very simple repair, I know it seems daunting- but I've installed thousands of helicoils in my time as a machinist. I have a soda can full of broken tangs- there is nothing to this repair except your anxiety about it is ramping you up
Its called a tang, and you can rinse it out with oil. You can also put a glob of grease on the tool to capture the tang when you snap the tang off. This is a very simple repair. I would not chase threads unless the lead thread of the pan has been damaged. You don't want to open up the minor or major diameter as the wire needs to be an interference fit in the pan
Timesert is absolutely a better repair, but based on what I have seen in this thread, the skill level necessitates just reinserting a helicoil and snapping the tang off. And even that process seems to be flying over some heads
This seems like the best advice. I am not against maybe going with a Timesert if this fails but I am just concerned about metal shavings in the pan as dropping the pan is not an easy job at all.
People on Facebook are recommending to retap before placing the helicoil but I think I'm just going to clean the threads well first with a light wire brush before considering retapping.
First time doing this, but we're also farmers so I don't think it's too daunting. Hell, I'm actively considering learning how to drop the pan if needed but I do know it will take me 6+ hours to do on my spare time.
Why would you need a torque wrench to snug up your drain plug. There isn't any pressure in the oil pan. A good washer, clean surface and gudntite is just fine. I have done hundreds and never had a leak.
Mistakes were made, I know. From my understanding, it snapped at 20nm which is roughly 15 ft-lb but I also realized that using a large torque wrench was a mistake as the readings at the low values are not accurate at all. Live and learn.
Can either be done DIY without a lift due to ground clearance?
I have it on Quickjacks currently so it's up about 2 and a half feet. We just had our shop built 2 years ago and I wanted to put in a 2 post but we had in-floor heating installed on the whole 5000 sq.ft pad so we opted out of it for now. May build a separate pad right next to the shop and make a small room specifically for a lift.
This seems like the best advice. I am not against maybe going with a Timesert if this fails but I am just concerned about metal shavings in the pan as dropping the pan is not an easy job at all.
People on Facebook are recommending to retap before placing the helicoil but I think I'm just going to clean the threads well first with a light wire brush before considering retapping.
First time doing this, but we're also farmers so I don't think it's too daunting. Hell, I'm actively considering learning how to drop the pan if needed but I do know it will take me 6+ hours to do on my spare time.
If you are just chasing the threads, there won't be much shavings. Probably not even as much as you may see on a magnetic drain plug. If you are concerned, pack the flutes of the tap with grease to pick up any stray shavings.
Considering that the last person has messed up the threads, I'd feel better about chasing the threads to make sure. Afterwards, install a drain valve so you don't have to keep taking the plug in and out.
Seems like you are putting too much torque on it. I use hand tight with my hand on the pivot point of the ratchet, never a problem.
I mean it snapped at 15 ft-lb but it's very much possible previous shops overtorqued this bolt.
My leading theory right now is that when I originally removed the drain plug, the helicoil (factory or aftermarket) came out slightly and when I went to reinsert the bolt, the end of the helicoil put pressure on the bolt head and caused it to snap. That's why in the first photo, you can see the broken bolt in the oil drain plug with the helicoil pointing out slightly.
I will know later today if inserting the new helicoil is sufficient and I will be placing a drain plug on it so I don't have to deal with this issue going forward.
I mean it snapped at 15 ft-lb but it's very much possible previous shops overtorqued this bolt.
My leading theory right now is that when I originally removed the drain plug, the helicoil (factory or aftermarket) came out slightly and when I went to reinsert the bolt, the end of the helicoil put pressure on the bolt head and caused it to snap. That's why in the first photo, you can see the broken bolt in the oil drain plug with the helicoil pointing out slightly.
I will know later today if inserting the new helicoil is sufficient and I will be placing a drain plug on it so I don't have to deal with this issue going forward.
15 ft/lbs should not cause it to snap unless it was weakened before.
Drain Plug snapped. Extracted it and helicoil came out
