You are very welcome. It was refreshing to follow your persistent willingness to dig in and press on! The 104 is one of the best engines I've ever seen and at my age that is many engines!

Good luck and thanks for keeping the thread up to date through its' conclusion.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

My Mercedes is still having burning smoke and smelling oil in the back of the rear engine area. I checked the valve cover bolts and four of them were loose, two on the each side in the rear engine area. Tightened two bolts on the valve cover on the rear engine area on each side of the exhaust manifold and the intake manifold area.

However, another two of the bolts (one of each side of the intake side and the other bolt on the exhaust side) were still not able to be tighten. I feared the inside thread holes on top of the clyinder head inside threads are stripped again. I thought the issue was resolved by putting in helicoils. When I removed the two bolts that were not tightened, I saw helicoills still attached on the end of each bolt below the bolt cover/sleeve. See the attached photo on this post, thread #1. The 2 blue circles on the inside valve cover indicates the locations of the stripped threads on the top of the clyinder head.

It seems the helicoils are not doing its job. If I go ahead and retread again and using helicoils at a greater size hole, I believe it will crack the head since the top of the clyinder head thread hole is rather small on its width size.I have three options:

1. Take off the valve cover and using JR Weld and fill in the two holes using a syringe and dowel to push in the mixture to make it solid and tight. After 24 hours to dry, use a threaded drill bit and drill inside the hole. The trick is the drill have to be very straight going down on the new thread hole so the new rebuild thread will work on the valve cover bolts.

2. optimusprime on this post, thread #9 wrote "Clean the holes out make sure they are clean and without any oil ,or the repair wont work .Fill the holes with plastic metal .Push the bolt in and let it set for a day .Then unscrew the bolt , Then ,clean the top of the hole flush .These are very low torque and if you over do it they will strip out in normal circumstances . I think 9nm to lock up . Put some hylomar blue on the gasket as well as you refit it. Also keep it all clean, or bits might get in to the oil"

Is optimusprime referring to Bondo® Plastic Metal, 5 ounce, Plastic Metal seals?


3. The other option is I am trying to avoid and that is to replace the head on top of the engine block with another head that have no issues on the inside threaded holes.

As for the three choices above, it seems that number 2 is the better choice. Any comments/feedback/advice is greatly appreciated.

Either one time or helicoil insert works in that spot, ITS 6 X1.0MM

nulu, thanks for responding. I think number 2 is the best route at this time. I will go ahead and do this bondo stuff. Also, here are the two locations of the stripped thread inside the top of the cylinder head. (color red circle) in the attachment below. I will continue to monitor and report my findings. Stay tune.

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I think this is the stuff used for the option 2. https://www.amazon.com/Loctite-442-28654-4-80ml-Thread-Stripped/dp/B000WSEUII

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Prost!

Search the parts diagram for your engine to determine how many bolts of each length are required and the exact location for each length in the head. You may be dealing with a simple misassembly issue.

The Helicoil coming out with the bolt is usually an indication that the hole was drilled out too large. It takes a great deal of skill to accurately drill out a hole with a hand drill with the head installed. Ideally it would be done with the head off on a drill press but that is a great deal of work.
You could try a longer Helicoil that would have more grabbing surface with the head.

Even with those 2 bolts not tightening fully you should not have the large amount of oil leaking that is shown in your pictures on another post. Maybe you should start over and pressure wash and degrease the engine and try to track down the source.

I thought you were taking it to a mechanic on the 15th.

Edit: I just saw your other thread where you explained why you did not take it to the mechanic.

Hirnbeiss, thanks for your helpful tip in your last post. Any other type of metal plastic bond/seals for threads out there as well that would work, specifically on the head thread issue?



ejboyd5, thanks for responding:

"Search the parts diagram for your engine to determine how many bolts of each length are required and the exact location for each length in the head. You may be dealing with a simple misassembly issue."



According to the parts diagram, it shows the length of each of the 2 bolts is the same size: M6 x 65 with washer (15 is the number showing the bolts and its location on the valve cover diagram). See the attachment image below under the section bolt diagram :



See attached photos below of the 2 bolts with helicoils that were removed. Notice the 2 bolts are the same size M6 x 65 with washer:


Rick76, thanks for responding in your last post. A longer Helicoils might work to replace the shorter helicoil I have on both bolts as indicated in the photos in the attachment. I am just keeping my options open as to what would be best to resolve this issue.

Rick76, "Even with those 2 bolts not tightening fully you should not have the large amount of oil leaking that is shown in your pictures on another post. Maybe you should start over and pressure wash and degrease the engine and try to track down the source."

Response. When I first started on this issue, I removed the plate cover over the spark plugs on top of the valve cover and there was a lot of oil inside. I cleaned up the oil in the surrounding areas near the wire packs, spark plugs,etcs., and replaced with a new valve cover gasket, including the spark plugs seals along with the half moon gaskets that goes back in the rear engine. Also, I replaced the fuel injector located in the front driver's side because the older fuel injector was missing its o ring and had a lot of oil on it.

I already cleaned up the engine area using the degreaser prior to tracking down the source of leaking oil.


in regards to the type of form a thread inside the hole on top of the head. Should I use Loctite 442-28654 4.80ml Form-A-Thread Stripped Repair Kit or Bondo® Plastic Metal, 5 ounce, Plastic Metal seals? Does it make any difference? Any other brand of form a thread that would work on repairing these particular threaded holes on top of the head?

What about replacing with a longer Helicoils with the same size that will fit on the bolt?

How about using a longer bolt than the current size M6 x 65 to replace using a longer or shorter helicoils without fracturing the top head hole thread? Can that be done and if so how much longer of the bolt size M6 x 65 that could possibly work?

if using a form a thread, where should the application goes? Inside the hole? On the bolt? Would putting on form a thread on the outside or inside of helicoils would work?

How about using a longer bolt size to replace the current size bolt? Would that work without damaging/fracturing the area around the bottom/top hole of the thread? If a longer bolt is advisable, what length should it be? Would using a longer helicoils or the same helicoils that I have now would work better with a longer bolt size? Sorry about repeating myself. Just to explore what are my best options at this point.

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Attached Files

01-0500 removing head cylinder cover.pdf (384.1 KB, 96 views)

Update:

I ordered Permatex 81668, a retread thread compound, online, since I have a hard time finding it in local stores. Also, I found another retread thread compound LOCTITE 28654 Stripped Thread Repair Kit, that does the same thing as well. Are there any other related retread thread repair kit that are similar to the ones like Permatex 81668 and LOCTITE 28654 Stripped Thread Repair Kit that are found in stores instead of ordering online?

I saw this youtube demonstration and from the looks of it, it appears to be a very good setup, less fussing,etc.

https://www.youtube.com/watch?v=B3WxsZxLqi0

https://www.youtube.com/watch?v=zUI6GMkTOjU


Check it for yourself and let me know what you guys think. The repair retread thread goes on the bolt and not the hole as demonstrated in the video. If that works, great.
Does this stuff really works to keep the valve cover bolts that goes inside the top cylinder head thread from stripping?

I am still waiting for the 3/8 socket torque wrench to show up so I can torque correctly on the bolts goes on the valve cover. This is why I have not been responding back lately, Stay tune.

Update: The torque wrench arrived two days ago and the Permatex 81668, a retread thread compound arrived yesterday. The torque wrench is impressive, in my opinion. Heavy and firm grip on the handle. Solid steel all around. Will see how this torque wrench performs.

After removing the top middle cover top on the valve cover, no oil is on inside the coil pack, wire sparks area, etc. See pictures 1 and 2. That is good news due to the fact when I first tried this job earlier, oil was everywhere before replacing with new valve cover gasket kit and replacing the fuel injector in the front facing on the driver's side, due to missing o ring.

While I removed the remaining 12 bolts on the valve cover, several of the bolts that goes on the valve cover, especially the front three bolts and the last two rear bolts, were not torque tight when reassembled the first time with new valve cover gasket kit. Then I remembered when I first put in the replacement valve cover gasket kit and after tightened the bolts, I droved the mercedes for a few miles. Afterwards, I did not checked the bolts again to the specific 10nm, since I did not have a torque wrench in the first place to re-tightened the bolts while the engine was still hot. Somewhere I missed/forgot to retorqued the bolts after the first time. Someone mentioned this somewhere. Always checked the torqued bolts first and second time after running the engine. Live and learn.

After removing the valve cover, I noticed a small opening on the valve cover gasket that was not set properly grooved inside the valve cover. See the pictures 4 and 5 below. The valve cover gasket loop facing on the passenger side rear engine. This could be the cause of the oil leaking dripping down on the exhaust manifold which resulted in burning and smoking oil. The gapped opening was big enough to cause a lot of oil to leak down along the side of the exhaust manifold and its pipe. Only after reassembled the valve cover gasket properly and set it in the groove will I know for sure that is the culpit.

Then it start to rain.... Stopped what I was doing until the weather is clear of rain. Mother Nature strikes again!!! Stay tune. .

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Here are the last two pictures of valve cover gasket on the valve cover rear end.

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Make sure that the groove where the gasket fits is clean. Many mechanics love to slop RTV everywhere. It should be removed for the seal to sit properly.

You may be well advised to start over with a new gasket.

The rain stopped. After checking the valve cover gasket and making sure it fits properly in the valve cover grooves, I put in the retread thread repair combo mixture along with the resistance fluid on the two bolts. In addition, I put in the threadlocker on another two bolts located in the rear valve cover that were the source of the oil leak (I believed). Soon after that, I torqued all the 12 bolts on the valve cover at 10nm crisscrossed. Fired up the engine and run at idle for a few minutes to warm up at normal temperatures 85c. Small puffs of smoke appeared on the passenger side rear engine. No burning oil or smell so far. I then droved the Mercedes for a few miles, returned home and checked for burning, smoking oil and leaks. No leaks, no burning oil and no smoke. I then tightened again the 12 valve cover bolts at 10nm while the engine is still hot. Problem solved, FINALLY!!!

As for the high idling issue, I found out that I was missing the fuel/gas cap. I bought a new fuel/gas cap. When idling now at its normal 800 rpm, it sounded like a shaking/rattling and low power when accelerating, like it needs a tune up or something like that. But that is another story at another time. I am just happy to resolved that nagging, persistent burning and leaking oil along with the smoke that had been bothering me for quite some time. However, I suspected it is a temporary band aid fix and I know exactly what the issue is if it pops up again and what to do about it. Thanks to all members of this forum who posted their comments/feedback/advice along with those who taking the time reading this post/threads.

Update on the high idling and rough idling issue with little power:

I did a troubleshooting code using my hand held code reader. I forgot the exact troubleshooting code as I remembered it was located on the coil wire/cable connection between the 3rd and 4th spark plug location. So I removed the valve top cover and saw the coil wire/cable was looose on the 4th spark plug area where the coil pack is located. Reconnected the looose coil pack wire/cable connector. Fired up the engine and back to normal. No shaking vibrations at idling and more power when accelerating. I must have knocked over the coil wire while reassembied the valve cover back on in its place. Issue resolved.