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DIY Stripped oil pan drain plug repair - Helicoil method

73K views 32 replies 16 participants last post by  gzig5 
#1 · (Edited)
Last time I changed the oil and tried to tighten the oil plug with a torque wrench, it just didn't feel right so I stopped. For a while it had a bit of a leak and now since it's time for the next oil change this would be the time to do some exploratory surgery.

For an alternative repair method, and a better more detailed write up than this one:
http://www.m5board.com/vbulletin/e3...5-diy-repair-stripped-oil-pan-drain-plug.html

1) First get the car up on some jackstands, remove obvious parts, gather your tools, etc.
I wanted to examine the drain plug as is, so I drained the oil from the oil level sensor, which was pretty messy. Then on to removing the oil pan. First thing I did after removal is put it into the parts washer and clean it. It's also a good idea to do this at the end and remove any dirt and metal particles before re-intalling.

2) Removing the oil plug and examining the threads, it looks like there is some minor damage, but I guess I got overly nervous when installing the oil plug. Nothing serious, and only a little bit of running torque - I can still turn the oil plug all the way by hand. Well, since I went through all the trouble of removing the oil pan, I might as well proceed with a preventative intervention.

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3) Now on to the repair. Best way to do this is set it up on a mill table if you have access to one. If not, a drill press is probably good enough. I would not recommend hand drilling! I set up dial indicator on the oil plug sealing surface. If it's badly pitted you want to take an end mill and renew the surface. Also you need to make sure that you are going to drill perpendicular to the surface and this will show any tilt that you may have. In my case it was flat and perpendicular to within a few thousandths of an inch, so I was good to go.

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4) The helicoil kit tells you what drill size to use. You can use a uniflute or some cone shape thing to center the hole. Then I locked the mill table in place and proceeded with drilling and tapping.

Water Glass Table Metal

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The heli-coils that came with the kit are way too long, so I cut a few of the coils off with a Dremel tool and removed the burs on the coil edge with a needle file. This picture is after I cut two turns off. I did a fit check and looks like I need to cut two more.
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5) Final result after helicoil install. The insert is just below the surface, and on the inside the tang breaks off exactly where the threads stop. Perfect fit! Drilling out the old threads does not affect the sealing surface at all. If you look closely you can still see some of the original chamfer. You don't lose any surface area between the pan and the copper gasket and the seal will work just as well as before and assuming you drill the hole straight.
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Metal Close-up Silver Macro photography Photography


The last two threads may block the oil from draining completely, but that's one of the issues with this repair. If you make the helicoil short enough to avoid that then you have only about two turns of the threads.



As a side note I think this oil pan is a really crappy design. I would have made the casting flat on the inside and then not machine away so much material for the hex head of the oil plug. So what if the oil plug sicks down another 1/4 inch? What genius designed this thing? The closeup photos show how porous cast aluminum really is. A threaded aluminum hole should always have a hard metal insert. That's just my opinion. It's also worth mentioning that if you don't have all the tools and equipment to do this right, you should find a good machinist to help you. You only get one shot at this and if you do it wrong, you've trashed a $400 oil pan.
 
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#3 ·
Thanks for the detailed write-up w/ pictures!
 
#7 ·
If you did that, there heli-coil would fail and come out in several pieces when you tried to tighten the plug.
 
#6 ·
When I bought my beast I noticed my copper crush washer didnt fit my drain plug at all, I started investigating and it looks like I have a mercedes drain plug installed, looks like someone stripped the threads and retapped it for a mercedes plug lol... I have a benz part on my car.
 
#8 ·
View attachment 116747

The last two threads may block the oil from draining completely, but that's one of the issues with this repair. If you make the helicoil short enough to avoid that then you have only about two turns of the threads.
Excellent writeup and pics! Unfortunately, the notch was what prevented me from doing this. That's a significant amount of oil that won't get drained if the notch is blocked - which would be the worst gunk that's left behind after every oil change.
 
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#9 ·
Correct me if I'm wrong, but doesn't the Helicoil instructions say to tap the notch off, with a chisel or flat-head screwdriver?
 
#12 · (Edited)
It's not if but when your drain plug threads fail

Regardless whether proper torque procedures are used, over time the aluminum threads will fail. Each time
the plug is tightened the resultant force on the inner edge of the pan's thread will deflect (pull) the thread
outward. When you remove the drain plug, it exerts pressure in the opposite direction. These deflections,
though small, will over time cause fatiguing, until eventually the yield strength of the weakened aluminum
is exceeded.

This pan should have never been designed without a solid, threaded insert. As a result, thread failure is just
a matter of time. There literally is no escaping this ultimate failure, no matter how carefully you torque to
the proper specifications.

Though I applaud the OP's concise procedure for installing the Heli-Coil insert, I would urge anyone that needs
to repair their oil pan drain plug to use a solid, threaded insert instead. The Time-Sert threaded insert repair is
far superior to a Heli-Coil, especially for aluminum and magnesium. They provide a one-piece, solid steel thread
rather than a spirally cut spring. In addition, these inserts are locked in position at both ends and the flanged,
outer face which seats into the counter-bored hole provides a direct surface contact for the drain plug's sealing
washer. Go to Time-Sert's website and check out the DIY videos for yourself and you will be able to see clearly
how this repair method is the proper way to go. Certainly, the Heli-Coil is far less expensive in terms of purchasing
the repsective repair kits, but in terms of performance and longevity there is really no comparison. Any proper
machine shop or high-end repair facility will have Time-Sert tooling and your cost will be the same as installing a
Heli-Coil.

I purchased the Time-Sert kit to repair my oil pan and it provided an absolutely bullet-proof repair.

Regards,
Alan
 
#13 ·
It was precisely that sealing issue that made me somewhat uncomfortable with the Time-Sert. The cost vs. Heli-Coil was not a factor. They cost about the same. I wanted to preserve the original oil plug seal in the process instead of having an outer seal on the Time-Sert flange and an inner seal made by the thread locking. And with the innermost threads doing the locking, I had to wonder how all that works with the drain cutout in the pan. If the copper washer is to seal against the pan, you have to get the Time-Sert flush to within a few thousandths of an inch. That means the counter-bore has to be precise. Not being familiar with the Time-Sert, I didn't know how to settle all these questions I had. Both Time-Sert and Helicoils have been used for this type of thread repair, but I would be skeptical that any data could support one having a better outcome compared to the other. Sure, there are anecdotal cases of people have good success and perhaps complications with either or both.
 
#15 · (Edited)
Nice

It was precisely that sealing issue that made me somewhat uncomfortable with the Time-Sert. I wanted to preserve the original oil plug seal in the process instead of having an outer seal on the Time-Sert flange and an inner seal made by the thread locking. And with the innermost threads doing the locking, I had to wonder how all that works with the drain cutout in the pan. If the copper washer is to seal against the pan, you have to get the Time-Sert flush to within a few thousandths of an inch. That means the counter-bore has to be precise.
Superfluid congrats on trying and succeeding with the Helicoil. I have to say though that I do think the Timesert is the better solution. Not being able to recreate that notch is probably the number one reason. fwiw the repair kit can be ordered with different depth inserts. If you get the shortest ones they come up just shy of the top of the 'bump' which works out perfectly re: the locking thread locations. When the inserts are driven in with their insert tool the last few outside threads (furthest from the ground) are expanded into the aluminum bump creating a permanent leakproof seal between the pan threads and the insert threads. No way in hell oil can get between the pan and the insert down there. I wish I'd taken a better pic of that end of the repair. And the conveniently low height means I hardly had to drill out any material at all to recreate the drain notch.

As for the flush top issue I think I overthought that. Even if I'd countersunk it a little the copper washer (being wider than the insert) would have been crushed between the drilled edge of the pan and the bottom of the plug. My edge is a little ragged too. I don't have a drill press so mine was done freehand (assisted by the bit alignment tube Timesert provides). A little JB Weld in the gap and sanded down nice probably would've negated my need to have to snug my bolt up to 30 lb/ft to crush the copper washer properly and stop the leak. I knew I could change to nylon washers if needed to have more 'meat' to fill the gap so I wasn't sweating it too hard.

Anyway hope your repair works/is working out 100%. Did you use any red threadlocker or anything to be sure the coil doesn't back out on you during oil changes?
TM
 
#16 ·
So far no oil leaks at the proper torque spec. We'll see how it goes with future oil changes. With a proper heli-coil repair there is zero running torque on the oil plug, so I'm not worried about the insert slipping. Also if the insert is damaged I like to be able to easily replace it, but that will probably never happen. For those reasons, I generally don't use adhesives with thread inserts. I will concede that a Time-Sert done with the right precision is a better repair than a heli-coil for this application but with my limited machining skills I went with the more idiot-tolerant approach. The best repair would be to bore out the oil plug section completely and put in a stainless-to-aluminum explosion weld or friction weld transition. Then you would have a solid stainless steel thread. :7: Sure, it's not cost effective, but that's all part of the fun.:thumbsup:
 
#17 ·
So far no oil leaks at the proper torque spec. We'll see how it goes with future oil changes. With a proper heli-coil repair there is zero running torque on the oil plug, so I'm not worried about the insert slipping. Also if the insert is damaged I like to be able to easily replace it, but that will probably never happen. For those reasons, I generally don't use adhesives with thread inserts. I will concede that a Time-Sert done with the right precision is a better repair than a heli-coil for this application but with my limited machining skills I went with the more idiot-tolerant approach. The best repair would be to bore out the oil plug section completely and put in a stainless-to-aluminum explosion weld or friction weld transition. Then you would have a solid stainless steel thread. :7: Sure, it's not cost effective, but that's all part of the fun.:thumbsup:
This is the method I used when I did did mine this summer but without the weld. Made a T-shaped bushing out of 304SS threaded 5/8-18 on the OD because that cleaned up the hole, was small enough not to remove the raised portion on the inside, and I had the tap. ID was threaded for the OEM plug. Bored the hole, faced the pan surface with an endmill so the bushing would seal flat, and threaded all in one setup so that the thread was straight and orthogonal to the pan surface. To install the bushing I used an old lug bolt, made a jam nut, threaded bolt into bushing and locked it into the bushing with the jam nut. The jam nut setup allows the bushing to be installed tightly without having to put a wrench directly on the bushing. I used red loctite on the threads which should be good to 550 degrees. I then bored an oblong hole through the side of the bushing to allow all of the oil to drain. I think this repair could be done on a decent drill press if you were careful. For those interested, I can post pics when I get home. I could also be coerced into making bushings or doing the complete repair for a reasonable fee.
Greg
 
#18 ·
Pics of oil pan bushing process.

Centering up bore with test indicator on the mill. Stainless bushing made on the lathe ready to go.


Boring out stripped threads (nothing left!) with small boring head. Could use drill in drill press.


Threading without moving pan and using center in quill ensures a straight hole.


Tapped hole. Chamfering hole and surfacing face not shown.


Bushing loctited in and cross drilled. New OEM plug installed in finished product. Pretty sure I'll be able to change the oil once a month and not wear this bad boy out.
 
#19 ·
Just curious, but you guys know there is a plug on the side you can remove to drain the oil in the event the "main drain" is screwed. Ive used that one a few times, but normally i just suck it out.
 
#22 ·
With a stripped plug thread the problem isn't draining the oil, it is keeping it in. The one on the side also does not allow all of the oil to drain. This repair takes an hour or two and saves spending $350 plug on a new part that is destined to fail again.
 
#21 · (Edited)
I've never been game to try these quick-drain gadgets ...

http://www.quickoildrainvalve.com/ProductDetails.asp?ProductCode=F109A

Has anyone else? I'd think that putting one in the bottom of the sump would be asking for trouble, but if there is a 'side-drain' as jt2ma71 suggested, it might be ok.

But I think a lot of workshops (at least in this country) use the suck-it-through-the-dipstick method now, so maybe that is the way to go. But how do you know you've got a complete drain??


.
 
#27 ·
Thanks for this wonderful DIY! While attempting to do an oil change last Thursday, the oil drain plug came out with pieces of thread... took a little searching to find the kit, but so far the fix seems to be working perfect!
 
#29 ·
What thread spec is this and why do you think it is better?
 
#31 · (Edited)
I should have been a little more clear, I believe it is better strictly in my opinion as my own M5 had the mercedes drain plug when I purchased it. I believe the coarser thread and larger diameter greatly reduces the chance to over torque and damage the threads.
 
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