Boards.ie uses cookies. By continuing to browse this site you are agreeing to our use of cookies. Click here to find out more x
Post Reply  
 
 
Thread Tools Search this Thread
01-08-2020, 22:31   #1
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
Crossed spark plug thread

I'm embarrassed to post this, but I think I damaged my cylinder head today on my W123.

I pulled the plugs to check them, they all came out easily. Putting the first one back (no 1), I thought I got a few turns by hand, then put the socket on it. After a few turns (too many) I decided it did not feel right, too hard. I went ahead with the other 5 (M110 engine, ali head) to compare, they all went in as expected, very easy. I then removed no 2 and tried that plug in no 1, just in case it was the plug, no joy.

My mate is a fitter, I rang him and he suggested a cleaning tap. We had a really bad phone connection so could not finish the conversation, will try again tomorrow. But in the meantime, what's your thoughts? I'm worried a tap will drop filings into the cylinder.

I know about heli coils (sp?) but any suggestions without removing the head?

Could I take a chance with a tap?

Yours. kicking himself, in Dublin
MrCostington is offline  
Advertisement
01-08-2020, 22:36   #2
Roger the cabin boy
Registered User
 
Roger the cabin boy's Avatar
 
Join Date: Feb 2020
Posts: 170
Quote:
Originally Posted by MrCostington View Post
I'm embarrassed to post this, but I think I damaged my cylinder head today on my W123.

I pulled the plugs to check them, they all came out easily. Putting the first one back (no 1), I thought I got a few turns by hand, then put the socket on it. After a few turns (too many) I decided it did not feel right, too hard. I went ahead with the other 5 (M110 engine, ali head) to compare, they all went in as expected, very easy. I then removed no 2 and tried that plug in no 1, just in case it was the plug, no joy.

My mate is a fitter, I rang him and he suggested a cleaning tap. We had a really bad phone connection so could not finish the conversation, will try again tomorrow. But in the meantime, what's your thoughts? I'm worried a tap will drop filings into the cylinder.

I know about heli coils (sp?) but any suggestions without removing the head?

Could I take a chance with a tap?

Yours. kicking himself, in Dublin
I think your mate is right.

Go give it to a car mechanic who has the right sockets and tools. There is a knack to finding the correct start of a thread that's damaged.

Last edited by Roger the cabin boy; 01-08-2020 at 22:40.
Roger the cabin boy is offline  
Thanks from:
01-08-2020, 22:43   #3
kadman
Moderator
 
Join Date: Feb 2005
Posts: 3,874
Thread chaser for clearing the thread, but as I am not familiar with MB engines , you will have to wait
for the MB experts to chime in.

I know from working on VW engines, that we used thread clearing taps , and oversize taps on damaged
plug threads. And often bored out 14mm damaged plug threads to 18mm.

Back in the day it was place sash cord into the chamber,bring up the piston, and tap the thread.
Any swarf acollected on the sash cord which was puled out with all the crap.

This was before helicoils.

But Like i said, best to get the advice from the merc men.

good luck with it.
kadman is offline  
Thanks from:
02-08-2020, 10:27   #4
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
Quote:
Originally Posted by Roger the cabin boy View Post
I think your mate is right.

Go give it to a car mechanic who has the right sockets and tools. There is a knack to finding the correct start of a thread that's damaged.
Thanks! I think I'd be able to trust my mate to do it, he looks after stuff in a plant hire company?
MrCostington is offline  
02-08-2020, 10:39   #5
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
Quote:
Originally Posted by kadman View Post
Thread chaser for clearing the thread, but as I am not familiar with MB engines , you will have to wait for the MB experts to chime in.
Sounds like there might be hope to fix without removing the head?

Does it matter what make the car is? I only mentioned the make as I was not 100% sure the head is alloy. I think it's safe to say you know your stuff!

Quote:
Originally Posted by kadman View Post
I know from working on VW engines, that we used thread clearing taps , and oversize taps on damaged plug threads. And often bored out 14mm damaged plug threads to 18mm.
Wow, I hope I don't have to do that!

Quote:
Originally Posted by kadman View Post
Back in the day it was place sash cord into the chamber,bring up the piston, and tap the thread. Any swarf acollected on the sash cord which was puled out with all the crap.
Is this a sash cord as used in house windows? So, if I understand, you push the sash into the cylinder and let it drop in there, then tap, then pull it out with a needle nose pilers?

PS great work on the VW!
MrCostington is offline  
Advertisement
02-08-2020, 11:51   #6
kadman
Moderator
 
Join Date: Feb 2005
Posts: 3,874
Heads on the VW are cast aluminium alloy, so soft enough to thread easily.

Soft enough for misaligned plugs to cross thread as well. Its common enough in the VW world
as the plugs may not always be easily accessible being a flat 4.

I am not Merc savvy, so I cant advise on the best course of action for you.

But if it can be done with engine in place on a flat 4 vw engine, I reckon an upright engine
is far easier.

I remember back in the 60's my dad boring out a 14mm cross threaded hole, and re tapping
an 18mm plug into the head on an old 1200 beetle. I thought nothing of it at the time,
but looking back with the tools available then, it was a feat.

Car drove for years after, I must ask him the full details of what he did then, and he could still do it now at 88
kadman is offline  
(4) thanks from:
02-08-2020, 12:15   #7
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
Is your dad free this afternoon?

Would you mind explaining the sash thing a bit further please?

I've just been looking at some videos where people seemed to put in helicoils without concern about debris, including Scotty Kilmer if you know him. He just started the engine to blow it out. I won't be doing that. But in the comments, it was suggested to put grease on the tap and clean after every few turns. My mate said that too.

https://www.youtube.com/watch?v=c_t2mz2tN3w
MrCostington is offline  
02-08-2020, 14:45   #8
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
I took some pics with a cheap endoscope, so not great quality.

The first one is the bottom of the thread showing the good part, second is the damage:



MrCostington is offline  
02-08-2020, 15:41   #9
kadman
Moderator
 
Join Date: Feb 2005
Posts: 3,874
Quote:
Originally Posted by MrCostington View Post
Is your dad free this afternoon?

Would you mind explaining the sash thing a bit further please?

I've just been looking at some videos where people seemed to put in helicoils without concern about debris, including Scotty Kilmer if you know him. He just started the engine to blow it out. I won't be doing that. But in the comments, it was suggested to put grease on the tap and clean after every few turns. My mate said that too.

https://www.youtube.com/watch?v=c_t2mz2tN3w
I just happened to post up pics of me placing case savers into magnesium alloy engine case.
I also used plenty of grease on both the drills and the tap, and placed grease
all near the hole.

With a cross threaded plug hole.
The sash cord was greased lightly and packed into the plug hole, with the piston near TDC. So that you did not need lengths of the cord. Then any tapping or drilling is done extremely gently and with care not to go beyond where you need to fix.

I have worked on vw engines with helicoils that gave trouble with helicoils loosening. This was because the early helicoils were basically wound wire. And this type have rounded edges where they grip into the new thread, so there is always the possibility of moving.
If you look at the case savers in my thread you will see how sharp the edges are, this gives a better bite into the new threaded hole.

As I have already mentioned, I am not merc savvy so in your best interests you should contact one of the merc savvy guys here before you proceed with anything and I am sure they have come across this problem before.

You wont be the first person to cross thread a plug
kadman is offline  
Thanks from:
Advertisement
02-08-2020, 16:43   #10
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
Hey, many thanks again.

I just looked at your pics, interesting. I hope I will get by with a cleaning. It will be Tuesday till I can get a tap.

Did you ever have problems getting the sash out?

I might post this on the MB club forum, but I've been pestering them over the last few days with some other questions!

Quote:
Originally Posted by kadman View Post
You wont be the first person to cross thread a plug
haha thanks
MrCostington is offline  
02-08-2020, 17:09   #11
kadman
Moderator
 
Join Date: Feb 2005
Posts: 3,874
Quote:
Originally Posted by MrCostington View Post
Hey, many thanks again.

I just looked at your pics, interesting. I hope I will get by with a cleaning. It will be Tuesday till I can get a tap.

Did you ever have problems getting the sash out?

I might post this on the MB club forum, but I've been pestering them over the last few days with some other questions!


haha thanks
Never had an issue, once you dont move the piston after you put in the cord.

Dont worry about posting questions on the MB owners forum.

Questions , questions, questions is what forums were made for, ask away...
kadman is offline  
Thanks from:
02-08-2020, 17:36   #12
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
Thanks!

OK I'll post there too, if they kick me out I'll say kadman made me do it
MrCostington is offline  
Thanks from:
02-08-2020, 20:42   #13
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
I got some replies on the MB club forum, mostly along what you already said (including your sash trick, but with a rag).

Suggested this tool, which is cheap and local

https://ige.ie/thread-chaser-set-2pc...SABEgL3ZvD_BwE

And this which looks like the winner, I think as it may, I think, push the debris upwards

https://www.sealey.co.uk/product/563...ad-chaser-14mm

I'll contact them tomorrow to see if I can get one here.
MrCostington is offline  
(2) thanks from:
02-08-2020, 23:19   #14
kadman
Moderator
 
Join Date: Feb 2005
Posts: 3,874
Reverse action tool is an ingenious bit of kit.

Let us know how that works for you,

good luck with it.
kadman is offline  
Thanks from:
03-08-2020, 16:13   #15
MrCostington
Registered User
 
MrCostington's Avatar
 
Join Date: Nov 2015
Posts: 605
Thanks kadman

Vinny Byrnes have the Sealey tool so I will pick it up tomorrow (I'm off this week). That is great as they are 15 mins from me.

Turns out the guy on the MB forum (mainly a UK club) that suggested it is from Galway!

UPDATE they have to order it for me, will be Thurs/Fri

Last edited by MrCostington; 04-08-2020 at 11:32.
MrCostington is offline  
Thanks from:
Post Reply

Quick Reply
Message:
Remove Text Formatting
Bold
Italic
Underline

Insert Image
Wrap [QUOTE] tags around selected text
 
Decrease Size
Increase Size
Please sign up or log in to join the discussion

Thread Tools Search this Thread
Search this Thread:

Advanced Search



Share Tweet