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1997 Mercedes 600 Coupe & 1995 500 Coupe, 2004 Yamaha R1 200hp 360 pounds
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Discussion Starter #1 (Edited)
I did the helicoil repair on the blown plug that stripped the cylinder head. I re-threaded VERY SLOWLY the cylinder head with the repair kit and all the shavings stuck to the kit used. I installed the new plug with the helicoil around it and it fit very tight and snug (like brand new). I was VERY careful and meticulaous on EVERYTHING especially making sure no shavings got into the pistons. Changed all 12 plugs to the bosch platinums and will eventually replace the other 11 coils and all other 11 coil wires (I did replace the 1 coil and wire on the blown plug). I also replaced the broken vaccum lines with better material (that took the most time trying to find where they connected).

She fired right up and sounds like I just drove her off the showroom floor. I hear NOTHING! I use to hear a small ticking noise (it was more annoying then anything) which was probably the bad plug or coil to begin with. I drove her around the block and the check engine light came on. So I disconnected the battery and reconnected it 5 minutes later to reset the computer. ALL lights are gone (no check engine light).

So I went for a test drive. I was a little paranoid so I babied her a little bit for about 10 miles but then I needed to know she was good to go again, so I got on the freeway and stepped on it until I got to about 90 and she was PERFECT. This thing is soooo smooth (literally like brand new).

Drove her back to the garage and gave her a hug. I am gonna have a full detail on her Monday but I must say it was good doing it myself. All the parts were about 200.00 and she runs BETTER then she did before the plug and coil blew out.

Thank you all for the kind words and the advise you gave me. Without this forum I wouldnt have known where to start, but once again another V12 M120 motor is running brand new and I probably saved several thousand in repairs by taking my time and doing it myself :thumbsup:
 

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vvee12 I'm glad to hear that your car is fixed and better than ever. :thumbsup: I liked the part when you mentioned you hugged your car. :D
 

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I did the helicoil repair on the blown plug that stripped the cylinder head. I re-threaded VERY SLOWLY the cylinder head with the repair kit and all the shavings stuck to the kit used. I installed the new plug with the helicoil around it and it fit very tight and snug (like brand new). I was VERY careful and meticulaous on EVERYTHING especially making sure no shavings got into the pistons. Changed all 12 plugs to the bosch platinums and will eventually replace the other 11 coils and all other 11 coil wires (I did replace the 1 coil and wire on the blown plug). I also replaced the broken vaccum lines with better material (that took the most time trying to find where they connected).

She fired right up and sounds like I just drove her off the showroom floor. I hear NOTHING! I use to hear a small ticking noise (it was more annoying then anything) which was probably the bad plug or coil to begin with. I drove her around the block and the check engine light came on. So I disconnected the battery and reconnected it 5 minutes later to reset the computer. ALL lights are gone (no check engine light).

So I went for a test drive. I was a little paranoid so I babied her a little bit for about 10 miles but then I needed to know she was good to go again, so I got on the freeway and stepped on it until I got to about 90 and she was PERFECT. This thing is soooo smooth (literally like brand new).

Drove her back to the garage and gave her a hug. I am gonna have a full detail on her Monday but I must say it was good doing it myself. All the parts were about 200.00 and she runs BETTER then she did before the plug and coil blew out.

Thank you all for the kind words and the advise you gave me. Without this forum I wouldnt have known where to start, but once again another V12 M120 motor is running brand new and I probably saved several thousand in repairs by taking my time and doing it myself :thumbsup:
Told you buddy ...
Not gonna be a headache if you take your time and are going to be care full.
Did you used the wire type or the insert type in the end?
Also you could have used silicone tubing as it stands up to heat better than the rubber or plastic lines. Vibrant makes the in various sizes and they are decently priced too.
 

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SEC 600 V12 2dr COUPE (RHD) One of the chosen few.
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Congrats.. welcome to the scuffed knuckles dirty fingernail world that is "V12 owners club"..we may not know it all..but its not brain surgery and we wont give money for nothing..
 

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F250 7.3TD Mercedes Benz W140 S600 1996 119k k's(sold), MB W124 300E 1989 261k k's(sold)
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Well done vvee12.
So, essentially the previous owner had stripped the thread on one of the plugs when they'd installed those 4 point plugs. And the ticking noise was the gas escaping from the cylinder - which also corroded the plug.

Congrats on keeping the Queen at 100%!
 

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current fleet: 1996 s500; 1997 BMW 328ic; 2000 Nissan Frontier; 1966 AC Cobra
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Congrats, what a great story - you are an encouragement to us all.

One underlying element - you are working with a quality automobile with quality parts and quality workmanship - you pay for what you get

As for me, I will always opt for older quality automobiles (since I can not afford new) over cheaply made new autos; and you can guess which ones they are. I have also learned the hard way that you can not trust their warranties, since they define the quality and not the buyer. Details are in the fine print and I can give you details on horror stories trying to work with substandard car companies.


Well done, alot of satisfaction on your part too - way to go
 

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1996 S600
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Excellent VV! Two observations and related questions: one always starts a plug by hand but especially in an aluminum head one wants to feel -- unfiltered by tools -- any resistance letting one know the threads are not aligned. Probably a slow and light touch is the important factor here. But with the M120, the intake's position will not allow this -- well, not without removing the intake! I clipped my plugs to the spark plug socket and fitted it to an extension and then spun the extension by hand -- figured this was the next best thing. How did you fit your plugs?

Second, maybe it's my size, but I had to climb on top of the engine to get to numbers 6 and 12 -- working from the side didn't work out for me. How did you physically manage to do all this work? I'm assuming you moved the harness tray, but it's still tight confines.

Maybe three observations/questions: the plastic vacuum lines so beloved of MB get friable with age and of course the high temperature. Did you replace with standard (expletive deleted) plastic line from MB or an alternative and if so tell us what you used?

Thanks again for an inspiring DIY journey.
 

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1987 560SL - 1994 S420 - 2005 S55 AMG
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Great Job vvee, I am glad to hear it was a minor repair. Did you take any photos of the helicoil repair that will be posted on the site?
 

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1997 Mercedes 600 Coupe & 1995 500 Coupe, 2004 Yamaha R1 200hp 360 pounds
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Discussion Starter #10 (Edited)
carjoy let me try and answer your questions..

1. the helicoil thread repair kit was a tool that was almost self aligning which made it easy for me to make the thread straight. I used a lot of force and did quarter turns at a time. I could almost feel the shavings come off the block so I knew it was doing its job. I just did it real slow and sometimes I would back out of the tool to clean the shavings off and start again. The tool came with a special lube to catch all the shavings so each time I backed out the tool to clean shavings, I would apply more lube. Once the tool got easier to turn I knew the new threads were created. This whole re-thread could have taken maybe 5 minutes but I took an hour or so taking my time to get it right because you only get 1 shot at it. Then the kit came with a new cover to screw into the spark plug and then screw into the bigger thread on the motor. It fit very tight and snug and I torqued it to 20 pounds I think.

2. Yes I did have to move the harness tray aside which was a bitch because there was a bracket the tray sat on which was almost impossible to remove. I wasnt able to remove the bracket so I "bent it" very slowly so that it could be used again. I dont know if you all know this but the hood latch has 2 settings. The second setting allows the hood to stand straight up instead of at an angle which was the reason I was able to get to that back plug. No way in hell could I have fixed it unless the hood was straight up. I am almost 6 feet 3 so using 2 or 3 socket extenders made it easier for me to get access. And yes I used the plug socket and the extenders BY HAND first to make sure they screwed on straight..

3. I replaced all the plastic vaccum lines with a high heat resistant rubber hose instead (it was reccommended by that mercedes mechanic in my first post). Following the lines was tough and VERY hard to get to but in time I got them all...

Like you guys said the stripped thread was from the previous owner having someone do a half ass job installing the wrong spark plugs in the first place, and stripping that one plug!

The whole thing was an all day project but saving 5 to 6 grand or even more, id say it was a productive day..... Sorry didnt get a chance to take pics because I was so focused on the repair itself..

This car literally drives brand new! as you can see shes smiling again :thumbsup::D:p;):cool::D
 

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1989 560sl, 2016 G63
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W140 Coupes

You know I always was a W140 sedan sort of fellow. But the more I look at y ours the more I wish I'd bought one instead of a 1998 S-600.

Well done on the DYI repair. I would not have been so brave as to have done that.

Cheers,

R.
 

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1997 S600 (sold)
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Very nice work. I just googled and read up on helicoil repair of spark plug threads. The grease trick to catch shavings is brilliant. That was my big concern with doing this repair with the head on the car. I was imagining all these little shards falling into the cylinder just waiting to sand blast the cylinder walls and valves. I learned something today.

Congrats!

And, unless you're having obvious problems with the other ignition coils, I don't see any reason to replace them. If it ain't broke...

Brett
 

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93 SL500, 95 SL320, 96 S320, 98 S500, 2002 E320 4Matic Wagon & A little 91 5.0 FORD Mustang
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Congratulations on you accomplishment, it feels great when the labor pays off.

I have a question. What brand, model number, and where did you get your helicoil thread repair kit. I'm in the whole San Francisco Bay Area several times a month, and next time I will pick one up-just to have on the shelf.

Thanks,

Martin
 

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1997 S600 (sold)
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And one parting shot before we move on. Let this be a lesson to everyone. It's always a good idea when you get a car that is new to you, to do a complete routine maintenance on it even if it supposedly isn't due and especially if you don't have maintenance records on the car. Assume nothing about the prior attention the car received. Get it fully service so it is "baselined" with regard to maintenance. This issue would likely have been completely avoided if the spark plugs had been changed out shortly after driving the car home. The necessary repair may not have been avoided because the spark plug threads may have already been stripped in this case, but the down time, possible tow costs (vvee12 was lucky that he was almost home.) and not to mention stress would have been avoided.

Brett
 

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1997 Mercedes 600 Coupe & 1995 500 Coupe, 2004 Yamaha R1 200hp 360 pounds
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Discussion Starter #15 (Edited)
And one parting shot before we move on. Let this be a lesson to everyone. It's always a good idea when you get a car that is new to you, to do a complete routine maintenance on it even if it supposedly isn't due and especially if you don't have maintenance records on the car. Assume nothing about the prior attention the car received. Get it fully service so it is "baselined" with regard to maintenance. This issue would likely have been completely avoided if the spark plugs had been changed out shortly after driving the car home. The necessary repair may not have been avoided because the spark plug threads may have already been stripped in this case, but the down time, possible tow costs (vvee12 was lucky that he was almost home.) and not to mention stress would have been avoided.

Brett
It had all the service records before I bought the queen and she was serviced by the same company for almost her whole life. It wasnt dealer serviced but a pretty decent mercedes or european repair shop down in LA which was very helpful getting me the service records before I bought her. I just think the mechanic who put the new plugs in last (wrong plugs by the way after hearing all the negative posts on 4 prong plugs) didnt take the time to seat them. I noticed when changing all 12 plugs that some were loose to come off and some were way to tight to come off. The 11 other plugs all looked like normal wear and werent as bad as the blown plug but I still think it was a rushed tune up job the last time she was done.

Like Brett says I dont know if I could have avoided the plug blowing since the previous mechanic stripped the plug in the first place, but I should have done a tune up on her within a week of buying her. I know we are not all certified mechanics but basic maintenance skills is helpful. I wont even change the oil on this car because of where the filter is and drain plug. I watched my mechanic do it and its worth a hundered bucks to have him do it.

I am still paranoid because of how smooth everything went. With all the posts I read on the cautions I needed to take and some even saying its a HUGE repair, it just was too good to be true that everything went so smoothly. I hope I dont nor anyone on this board have this problem ever again. It was stressful to say the least with it either costing me 200 bucks to fix or 6 or 7 thousand for my mecahnic to fix..

I googled trying to find a price on a new M120 cylinder head. I found one for 1700 bucks and who knows how much labor it is to install one :bowdown:
 

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I am still paranoid because of how smooth everything went. With all the posts I read on the cautions I needed to take and some even saying its a HUGE repair, it just was too good to be true that everything went so smoothly. I hope I dont nor anyone on this board have this problem ever again. It was stressful to say the least with it either costing me 200 bucks to fix or 6 or 7 thousand for my mecahnic to fix..
It just goes to show that many of us don't know what we're talking about half the time. :) But, we still have plenty to say. Adrian was clearly spot on, and he's the one with real experience. Anytime I give advice I always try to remember to qualify it with my level of actual experience. In this case I had none. I hadn't even seen it on TV, but I had read about it. :)

Brett
 

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1997 Mercedes 600 Coupe & 1995 500 Coupe, 2004 Yamaha R1 200hp 360 pounds
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Discussion Starter #17
thats why EVERY opinion and input matters. This forum even helped me choose the right plugs (I didnt know which was best). I just took everyones opinion and made my own decision and fortunately it worked out. Sometimes it may not. I especially value your opinion Brett because Ive seen how much you have helped others. Its people like you and the MANY others that have saved me thousands and saved others as well.

Now I hope my experience can help save another M120 owner thousands as well if they incounter the same problem..
 

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89 BMW E34 ///M20 525i
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thats why EVERY opinion and input matters. This forum even helped me choose the right plugs (I didnt know which was best). I just took everyones opinion and made my own decision and fortunately it worked out. Sometimes it may not. I especially value your opinion Brett because Ive seen how much you have helped others. Its people like you and the MANY others that have saved me thousands and saved others as well.

Now I hope my experience can help save another M120 owner thousands as well if they incounter the same problem..
Wow, I'm that much more in envy of you V12 coupe owners. I'm working my ass off to buy one of those beautiful machines.

If you ever have any DIY questions about the detail work you mentioned, let me know. I'd be more than happy to help you find the most gentle, yet effective procedures to care for your girl.

PS-lol @ hugging. :D
 
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