HELP Spark plugs will not screw in - Page 6 - Mercedes-Benz Forum
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post #51 of 74 (permalink) Old 06-10-2018, 02:47 PM
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Congratulations, I am glad it turned out such a great success and thank you for sharing with us what you did and how you did it to correct it.
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post #52 of 74 (permalink) Old 06-11-2018, 06:21 AM
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I'm glad it all worked out well.

For anyone from the future reading this, I'll just say, I've probably installed more than 50 helicoils in spark plug holes in aluminum heads, and, while you should be cautious, you really don't need to go to all these lengths to prevent damage to the cylinder. As long as the debris is small enough to prevent it from being squeezed between the piston and the head, it'll all blow out the exhaust valve the first you turn the engine over. If you put grease on the tap, it's unlikely that anything will end up in the cylinder anyhow. If you want the belt and suspenders approach, position the crank so the piston is approaching the top of the exhaust stroke before you start and blast air in through the plug hole after you're finished.

TMSAISTI...
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Last edited by John350; 06-11-2018 at 06:34 AM.
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post #53 of 74 (permalink) Old 06-12-2018, 01:24 AM
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Congrats, HardwayMB! Glad it all worked out! And a testament to the support of the great community here.
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post #54 of 74 (permalink) Old 06-12-2018, 03:20 PM
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Originally Posted by John350 View Post
I'm glad it all worked out well.

...As long as the debris is small enough to prevent it from being squeezed between the piston and the head, it'll all blow out the exhaust valve the first you turn the engine over. If you put grease on the tap, it's unlikely that anything will end up in the cylinder anyhow...

TMSAISTI...
My concern was with a bit of shaving getting trapped between the cylinder wall and the piston, or potentially fouling a ring somehow. No chance of that or are you counting on the soft alum not harming the cylinder wall?

Bottom Feeding Belt & Suspenders guy. One-timer with the Helicoil.
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post #55 of 74 (permalink) Old 06-12-2018, 07:40 PM
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Anything's possible, I suppose. Although, aluminum won't hurt the steel cylinder.

John
"Real engines don't have spark plugs!"
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post #56 of 74 (permalink) Old 05-05-2019, 01:16 PM
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Resurrecting this old thread as it seems I have the same issue on #8. All the other plugs were cake, then #8. It seems a prior plug change was botched and left uncorrected. I am ordering the back tap mentioned and used by @HardwayMB - fingers crossed it works. #8 is not the easiest to access. Also thanks to the community for taking the time to post and comment on these issues. I would be lost without.
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post #57 of 74 (permalink) Old 05-05-2019, 02:02 PM
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Originally Posted by Silversun262 View Post
I am ordering the back tap mentioned and used by @HardwayMB - fingers crossed it works. Also thanks to the community for taking the time to post and comment on these issues. I would be lost without.
On the strength of this thread, I ordered a back threads chaser too..

Good luck, man.

MBL
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91 500SEC EURO Germany
87 560SEC USA 49 State Version
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post #58 of 74 (permalink) Old 05-06-2019, 03:05 AM
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Do the same as a chaser,, by cutting a slot down one side of an old spark plug .
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post #59 of 74 (permalink) Old 05-08-2019, 05:52 AM
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Good thread certainly, I have seen many aluminum heads ruined by cross-threaded plugs. Take you time and use the "feel" method, even someone with limited experience can feel threads starting to bind..always use common sense and don't force it. I always use a dab of anti-seize as well.
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post #60 of 74 (permalink) Old 05-08-2019, 08:55 AM
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Good thread certainly,

John
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