Spark Plug Tester - Page 2 - Mercedes-Benz Forum
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post #11 of 28 (permalink) Old 11-30-2018, 11:28 AM Thread Starter
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Jyuma, how bad is it / off compared to other cylinders?
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post #12 of 28 (permalink) Old 11-30-2018, 12:11 PM
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Quote:
Originally Posted by miko1aj View Post
Wow 50/50.... I knew I was in trouble when I removed the #6 spark plug, it came out too easy - see the attached pic, I think some adhesive or loctite might have been used to help it stick in place.

This is the first time I've replaced spark plugs in the M117 engine, and in hindsight I think that the problem with #6 (or #5 for that matter) is that it's too easily accessible compared to other cylinders where you really have to be flexible and careful not to drop the plug or cross thread it etc. I imaging someone before got lucky screwing plug #5 with a socket driver and went on to plug #6 where the luck ran out abruptly....

If you don't mind could you share a little bit about the helicoil experience please - did you install it with the engine in TDC, or removed the block, or just went at it as-is in situ? Helicoil is uncharted territory so I'm looking to educate myself before tackling this issue... Any advice, tips or guidance is much appreciated!
Helicoil is not the only manufacturer of thread repair. You drill and tap a precise larger hole then screw in the helicoil with a special tool, break off the tab. But you also need a jig to hold the drill bit square to the cylinder. You need lot of high pressure air to blow the hole clean, you grease the tap to hold the majority of the shavings, you should have an borehole camera they are cheap nowadays, you use wd40 to help wash debris clear, and a strong vacuum cleaner, and before you insert the plug crank the engine to do a final blow out of possible shavings. Wear safety glasses. I used a thread repair kit from a company called Mountain they are better than helicoil for this application, there is no tab to break off on their inserts. Timesert is another company superior to helicoil, like Mountain it it is a fully formed insert and not just a wire coil.

Another thing is that not all blowguns are created equal, most will not be able to blow sufficient air into the cylinder to blast out the metal shavings. Harbor freight has a long extendable blow gun that does blow with great volume.

Last edited by ot1; 11-30-2018 at 12:34 PM.
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post #13 of 28 (permalink) Old 11-30-2018, 12:53 PM Thread Starter
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Thank you ot1, that's very solid advice. I'll shop around for the brands you mentioned. In the meantime I've watched a couple of YouTube videos, it doesn't seem rocket science but I am worried about the fact that I only have one shot to get it right, and not sure yet how I feel about practicing on a 40 year old aluminum block....

I assume you did it on the engine as is, without removing it? In hindsight I should probably consider myself lucky the issue is not with cylinder 3/4 or 7/8 as that would be just too much.
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post #14 of 28 (permalink) Old 11-30-2018, 01:11 PM
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Quote:
Originally Posted by miko1aj View Post
Wow 50/50.... I knew I was in trouble when I removed the #6 spark plug, it came out too easy - see the attached pic, I think some adhesive or loctite might have been used to help it stick in place.

This is the first time I've replaced spark plugs in the M117 engine, and in hindsight I think that the problem with #6 (or #5 for that matter) is that it's too easily accessible compared to other cylinders where you really have to be flexible and careful not to drop the plug or cross thread it etc. I imaging someone before got lucky screwing plug #5 with a socket driver and went on to plug #6 where the luck ran out abruptly....

If you don't mind could you share a little bit about the helicoil experience please - did you install it with the engine in TDC, or removed the block, or just went at it as-is in situ? Helicoil is uncharted territory so I'm looking to educate myself before tackling this issue... Any advice, tips or guidance is much appreciated!
I had an issue with my #6 (and #8) plugs feeling like they were cross threaded. I bought a Spark Plug Thread Repair Tool by Powerbuilt for 14mm holes. It worked perfectly. It is opposite of a thread chaser. You insert the collapsed tool into the spark plug cylinder hole then you expand the tool. Here is a video link and a photo of the tool.
This beats helicoil repair if it works.

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post #15 of 28 (permalink) Old 11-30-2018, 01:34 PM Thread Starter
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Thank you Tom, that's the reverse chaser which I tried today, it's a clever little yoke but unfortunately it did not work for me - it went in nicely, but as I was winding it out I could feel it wasn't tight on the thread, it was fully expanded but there's just not enough "meat" on the thread... Afterwards I got the spark plug in but it just wouldn't tighten anymore, it's wobbly.

This situation breaks my heart may I add 😞
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post #16 of 28 (permalink) Old 11-30-2018, 01:54 PM
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Quote:
Originally Posted by miko1aj View Post
Thank you ot1, that's very solid advice. I'll shop around for the brands you mentioned. In the meantime I've watched a couple of YouTube videos, it doesn't seem rocket science but I am worried about the fact that I only have one shot to get it right, and not sure yet how I feel about practicing on a 40 year old aluminum block....

I assume you did it on the engine as is, without removing it? In hindsight I should probably consider myself lucky the issue is not with cylinder 3/4 or 7/8 as that would be just too much.
Yes without removing the head. I cant imagine a crossthreaded plug holding the force of combustion or sealing properly. Once you see the threads are damaged with a borescope USB Hooked to your smart phone are the cheapest, you can determine if the threads require an insert. The drilling and tapping into aluminum does not require a power drill so you could get to back plugs using a ratcheting collet or a 12 point ratchet to grab the square drive tap. You have to use a cutting oil not any old oil but cutting oil, this is also critical. Dry threads could likely crack.
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Last edited by ot1; 11-30-2018 at 03:22 PM.
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post #17 of 28 (permalink) Old 12-01-2018, 08:00 AM Thread Starter
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Thank you ot1, this is great advice. My definitely require an insert or helicoil as, after reverse chasing the thread, I'm able to screw in the plug but it won't tighten, not enough threads to hold it in place - as you mention it won't seal properly and I'm pretty sure it will reach outer space as soon as I crank the engine - ;-)

I took a look and the best fit I can find is this baby: TIME-SERT M14 X 1.50 Metric Thread Repair Kit 1415 https://www.amazon.com/TIME-SERT-Met...=Timesert++m14

Regarding Mountain I can only see repair kits for Ford which are not metric - strangely I can't even find the Mountain website either? Could you let me know which set you used and where you got it please?
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post #18 of 28 (permalink) Old 12-04-2018, 08:31 AM Thread Starter
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Hi everyone,

After extensive consultation (thanks to all for your feedback) I've decided to go for the Timesirt kit 4412-321 M14 x 1.25, which has all the tools and the correct threads required for the repair.

There's a fantastic series of videos on YouTube by realfixesrealfast how to do this job properly, with this one especially worth viewing and sharing:

I should have the kit next week - early Christmas! - and will aim to do the repair over Christmas break.
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post #19 of 28 (permalink) Old 12-05-2018, 03:26 AM
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Here is another video on the subject.



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post #20 of 28 (permalink) Old 12-05-2018, 03:31 AM Thread Starter
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Indeed riffraffjazz is a great guy to follow - a lot of useful hands-on DIY information especially if you've a 450 or a newer 300. Subscribed
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