Heli-coil advice requested - Page 3 - Mercedes-Benz Forum
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post #21 of 39 (permalink) Old 05-26-2019, 04:44 AM Thread Starter
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Liviu165 is right on the timesert but also it not only needs a chamfer but the surface of the thing you are doing needs to be countersunk with a special tool so the gasket will seal. For what you are doing I would stay with a helicoil. I am sure you have enough meat on the head to fix things. Keep us in the loop. Actually I think it was timesert that had the oversize insert, not helicoil.
I leave soon for a trip with my brother. That vehicle will now sit for a month.

I have enough time to investigate something I read about on my parts vehicle head. A saturated solution of Alum (ammonium aluminum sulfate) is supposed to dissolve ferrous bolts without damaging the aluminum head. I will try this on the same head bolt that also sheared on my parts vehicle. The head is sitting on my workbench so I only need to go to the grocery store to see if McCormick Alum has the correct chemical composition. If not then I will buy some off of eBay.

I still have M10 helicoil and the head from my parts vehicle as options for me.

I'll update the board sometime in June.
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post #22 of 39 (permalink) Old 05-26-2019, 05:36 AM
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I still have M10 helicoil and the head from my parts vehicle as options for me.
I'm confused; if you're going oversized, why use a helicoil? Also, 3/8" is slightly smaller than M10.
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post #23 of 39 (permalink) Old 05-26-2019, 05:46 AM Thread Starter
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I'm confused; if you're going oversized, why use a helicoil? Also, 3/8" is slightly smaller than M10.
John, I figure that I have only one shot at the helicoil in the vehicle. If I go with the 3/8" helicoil and it fails then the tap out from the 3/8" will prevent me from stepping up to M10 helicoil. At least that is my understanding.

I need to be educated! Thanks-Tom
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post #24 of 39 (permalink) Old 05-26-2019, 12:20 PM
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If you're cutting new threads, you won't need a helicoil. The only reasons to use the helicoil are to repair damaged threads, or to provide a better thread for a part that is regularly disassembled.

OBTW, I don't know how far off your drilling is, but, I will confess to having installed heli-coils in less than perfect holes, with acceptable results. I mean, it's not like the intake manifold is a high stress component...
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post #25 of 39 (permalink) Old 05-26-2019, 01:28 PM
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I agree with John in that this area is not critical in getting it perfectly correct, but I also went into the garage and looked at the M-10 and M-8 helicoil. I found you can actually double them if you want to get back to the original thread size and need to drill out to a larger size. That is drill it out bigger then put the large helicoil in then an 8 in the same hole which the larger helicoil is in.. I confess I have not tried this for durability, but no reason why it would not work.
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post #26 of 39 (permalink) Old 05-26-2019, 04:53 PM
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I'm not sure how you determined that, but, absent data from Helicoil, I'd want to try it on a junk piece of aluminum first. I think it would be an incredible coincidence if the tap for an M8 Helicoil cut M10 threads (if I understand what you're saying.)
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post #27 of 39 (permalink) Old 05-27-2019, 06:03 AM
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If one thinks M8 helicoil could fit inside M10 helicoil then one should compare taps for those helicoils as helicoil taps have the same pitch as screws. Coarse m8 should have 1.25 mm pitch and coarse m10 should have 1.5 mm pitch. M10x 1.25 thread also exists.
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post #28 of 39 (permalink) Old 05-27-2019, 01:13 PM
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John, here is a picture of a M-10 x 125 helicoil and a M-8 x 125. The second picture show one being threaded into the larger one. Now I donít know how strong it would be but if he is insistant on a standard size you could do this. Time sert also makes something called a large sert, which would work as well. When I did the heads I helicoiled all the bolt holes. The kit had lots in it and I figured I might as well when it was apart.
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post #29 of 39 (permalink) Old 05-27-2019, 04:10 PM Thread Starter
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John, here is a picture of a M-10 x 125 helicoil and a M-8 x 125. The second picture show one being threaded into the larger one. Now I donít know how strong it would be but if he is insistant on a standard size you could do this. Time sert also makes something called a large sert, which would work as well. When I did the heads I helicoiled all the bolt holes. The kit had lots in it and I figured I might as well when it was apart.
I have ordered the M10-1.25 helicoil kit and a M10-1.25 40mm hex socket head stainless steel bolt. Also a 13/32" cobalt drill bit. The bit has arrived, the other parts are forthcoming. As mentioned earlier I will not get back to this project until late-June.

Inserting a M8-1.25 helicoil into a M10-1.25 helicoil should not be necessary for me since I intend to drill out the manifold bolt hole to M10 size.

I was not impressed with the Alum solution dissolving ferrous bolts. It takes way too long for that option to be seriously considered.

My parts vehicle right hand side head is sitting on my workbench and will be an option if the M10 helicoil fairs. If any of those bolts become problematic (as mentioned by Liviu165) then from my perspective it is game over.

I do have a question about that option. What would be needed to transfer my low mileage camshaft onto the high mileage head? Is there someplace that specializes in that task?
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post #30 of 39 (permalink) Old 05-27-2019, 04:30 PM
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What would be needed to transfer my low mileage camshaft onto the high mileage head?
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?

Last edited by liviu165; 05-27-2019 at 04:35 PM.
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