Heli-coil advice requested - Page 4 - Mercedes-Benz Forum
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post #31 of 39 (permalink) Old 05-27-2019, 04:30 PM
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The helicoil changes size (gets smaller) when you thread it into the specially tapped hole. This is what helps keep them from unthreading when you remove the fastener. It is not reasonable to assume that, because one threads into the other on the bench that it will do the same thing in use. If that were the case, then the M8 helicoil tap would be exactly the same as a standard M10 tap, and it is not. If you don't believe me, screw the M8 helicoil onto an M8 bolt and you will see it is a very loose fit.

If you're planning to use M10 hardware, you can just drill and tap the original hole for M10; no need to go oversize then back to the M10 helicoil.
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post #32 of 39 (permalink) Old 05-27-2019, 04:42 PM Thread Starter
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To make that swap you need to remove all 5 towers (camshaft bearings) in order to extract the old camshaft. THen you install the new camshaft with either the old towers or the newer ones. However, be advised that each tower has one bolt that goes all the way into the block. If you strip the aluminum threads into the block, then you are in for a very costly repair (remove the head, use helicoils and the drilling jig). Question: Do you think is worth the risk?

In addition, by installing a different camshaft you'll have to adjust the valve pucks again, according to the new cam. Question: Are you willing to complicate your life with that operation? If in doubt, just ask Stutz.

So, isn't a better idea just to leave it the way it is?
It is my understanding that if the helicoil fails then I MUST remove the head. I would not be able to put the intake manifold back on the engine if that one bolt is absent. Is there another option available to me?

What would I have to lose by removing the head. I would have a non-functional vehicle without that intake manifold bolt. If the threads in the block strip then it would be game over for me.

I really am up against a wall.
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post #33 of 39 (permalink) Old 05-27-2019, 05:33 PM Thread Starter
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The helicoil changes size (gets smaller) when you thread it into the specially tapped hole. This is what helps keep them from unthreading when you remove the fastener. It is not reasonable to assume that, because one threads into the other on the bench that it will do the same thing in use. If that were the case, then the M8 helicoil tap would be exactly the same as a standard M10 tap, and it is not. If you don't believe me, screw the M8 helicoil onto an M8 bolt and you will see it is a very loose fit.

If you're planning to use M10 hardware, you can just drill and tap the original hole for M10; no need to go oversize then back to the M10 helicoil.
John, I thought the helicoil tap for the M8 insert that I already tried exceeded the limits for a straight M10 tap. I suppose I could try and if it fails then helicoil tap for M10 at that point.
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post #34 of 39 (permalink) Old 05-27-2019, 05:36 PM
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It is my understanding that if the helicoil fails then I MUST remove the head.
Correct.

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I would not be able to put the intake manifold back on the engine if that one bolt is absent. Is there another option available to me?
Not really. That's why you have to make it work.

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What would I have to lose by removing the head.
A lot if things don't come up right afterwards. It will also be a costly repair.

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If the threads in the block strip then it would be game over for me.
Not really, you can still use your block but things will require much more work. Basically you will walk the same path that Stutz did.

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I really am up against a wall.
You can put it that way, but the fact that you are aware of the challenge, its ramifications and your options, all together are to your advantage. I hope all that will help you in solving your problem.
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post #35 of 39 (permalink) Old 05-27-2019, 05:41 PM
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I hope you don't mind me asking, but can you please post few very close-up pictures (from different angles) and very clear of what you have right now? We've talking for over 30 posts, but none of us has seen what you actually have there. just saying.
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post #36 of 39 (permalink) Old 05-27-2019, 05:52 PM Thread Starter
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I hope you don't mind me asking, but can you please post few very close-up pictures (from different angles) and very clear of what you have right now? We've talking for over 30 posts, but none of us has seen what you actually have there. just saying.
Liviu165, I put all of the pieces back into place since I will be gone for a month. They are not torqued but just lightly bolted into place. My memory requires this unnecessary step along with lots of notes and plastic baggies marked with specifics. When I return next month then I will take it apart again and get close ups. I am also recruiting a person with better mechanic skills than my own to help when I get back.

I want to thank everyone on this board who has contributed to my education. Yes, I make mistakes. Without this board I would not even try these tasks. I will keep trying until I am completely out of affordable options. There is a finite limit on how much money I will pour down this hole.
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post #37 of 39 (permalink) Old 05-28-2019, 05:24 AM
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John, I thought the helicoil tap for the M8 insert that I already tried exceeded the limits for a straight M10 tap.
I'm confused. Are you saying you already installed an M8 helicoil and it failed?

The drill size for an M8x1.25 helicoil is 8.3mm. Drill size for a 3/8"-16 tap is 7.94mm. Drill size for a 3/8"-24 tap is 8.33mm. The drill size for an M10x1.25 tap is 8.9mm. The drill for an M10x1.25 helicoil is 10.3mm .

If you've already tapped the hole for the M8 helicoil you cannot go the the 3/8" bolt as the pitch is different. Next thing to try would be the M10x1.25 tap and bolt, not the M10 helicoil.

The M8 time-sert is also an option as it uses a larger hole than the helicoil (also 10.3mm) and would restore things back to standard size.

Last resort is to have someone silver solder the hole shut and start over. You could do that on the car, in fact, a skilled welder could TIG weld it, too.

Last edited by John350; 05-28-2019 at 05:33 AM.
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post #38 of 39 (permalink) Old 06-22-2019, 03:37 PM Thread Starter
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I hope you don't mind me asking, but can you please post few very close-up pictures (from different angles) and very clear of what you have right now? We've talking for over 30 posts, but none of us has seen what you actually have there. just saying.
I am back working on my intake manifold project. Here are two pictures of the hole before and after the M10-1.25 helicoil insert. All of the intake manifold bolts were torqued to 23Nm torque. Howerver, after sitting for a few hours I came back and checked them again. All of them needed some additional torque; some needed a lot. The helicoil insert M10 bolt required the least amount of re-torque. I read other threads where the user retorqued his intake manifold bolts for several days before everything stayed put.
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post #39 of 39 (permalink) Old 06-22-2019, 03:53 PM Thread Starter
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During reassembly of the lower and upper intake manifold pieces I decided to do the work in the engine bay. I loosened the EGR tube at the exhaust manifold connection and rotated the EGR tube upward in the engine bay while it pivoted at the EGR valve. I stuck a 2x4 block of wood under the bottom manifold piece for additional support. I hooked up the EGR tube to the bottom piece then attached the top manifold piece and bolted things together with three of the long bolts. This allowed me to check the eight gaskets for proper seal. The block of wood kept everything off of the new gaskets until I was ready to lower into place. A slight lift of the assembled intake manifold allowed me to easily remove the block of wood. It was easy to manage by myself.
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