M116 Valve train- source of engine noise??

1982 380 SL 133K

I purchased this car with a terrible engine noise that sounded to me like a rod or wrist pin. Very pronounced hammer like noise upon start up that seemed to diminish with increasing engine speed (as in when I drove it home-9 miles). I thought the noise was just being covered up with all the other engine /driveline noises and that may have been true.

I finally was able to get the engine mounted on a stand over the long weekend. I removed the oilpan and cam covers. The previous owner had taken the car to an independent garage and they had diagnosed the noise as a bad rocker arm. They went through the valve train and supposedly changed out rocker arms (number unspecified by previous owner and he didn't have a bill at the time of sale). Whatever they did they didn't eliminate the noise and told the owner that they thought for sure it was the rocker arms.....

I made the mistake of assuming they had eliminated the valve train as the source of the noise (and believe me it is much louder that any valve train noise I have ever come across). I found it haed to believe it was a rod or wrist pin at that mileage, but knew anything was possible..

Today I took the time to go over the components in the valve train and noticed the exhaust rocker arm on #6 was sitting lower than any of the others. With the cam lobe pointed up I was able to move the rocker arm up and down 1/8". The valve clearance compenstor was not supporting the rocker arm. Notice how low the rocker arm on the right is sitting on the compensator. As indicated I can wiggle it around and the total movement up and down is 1/8".

So the questions have to be:

What has happened here? Obviously the previous owner was ripped off in that there is a problem with the rocker arm.

The important question has to be would this tremendous amount of clearance be responsible for the loud hammering I was experiencing??

What would be the procedure for repairing this problem? Remove the cam , rocker arm and compensating device? Replace compensating device and rocker arm with new and adjust? Any special tools or procedures in replacement of compensating device(I'm new to Mercedes).

Sorry for the long post but I wanted to lay the whole deal out as much as possible. Thanks for any input, advice, or suggestions.

Randy

[ILUVMILS]

It looks like the compensating element collapsed. It's quite easy to replace, just be sure to torque it properly. I'd look carefully at the rocker arm as well. Pay close attention to the area in contact with the element. And yes, that much freeplay/wear will cause one heck of a noise. Good luck

I went back to the engine and checked the remaining rocker arms and found that the exhaust rocker on #5 was loose as well. It was not quite as bad as #6 (1/8") but very loose. Are these normally tight like the rest or is it possible that the device has collapsed due to the fact that all the oil has drained from the engine? It has been upside down and in every position while on the stand.

Is there a tool that I can compress the valve spring with in order to remove the rocker arm and then the compensating device without removing the cam?? Any idea where I might rent or purchase said tool?

Randy

[ILUVMILS]

With the respective cam lobe pointing up, there shouldn't be any free-play of the rocker arm. Remember, that's the whole idea! Inspect the cam lobes and rockers VERY carefully for wear. I seriously doubt turning the engine over on a stand allowed the element to collapse. There is a spring compressor made for this job by MB and it works great. I don't know if you can rent one, but maybe you could look at the tool at your local dealer. At least you'd know what it looks like and what else might work. It really makes no difference because you need to remove the rockers BEFORE you remove the camshaft so you've got to find a suitable in any event. You'll also need to find the guage to check correct pre-load of the element after you're done. It's simply a little doo-dad that fits over the rocker and checks installed height. If it's out-of-spec you can adjust it by changing the spacer that sits on top of the valve spring retainer. Do some research before-hand so you know what to expect. It's a very easy job as long as you're prepared. Good luck

Thanks for the additional information. I found another collapsed ball stud after I made the post. I did in fact stop by my local full service auto supply store this afternoon and looked at the KD3087 spring compressor. It seems to be the same design as the MB tool. I have also been in contact with someone concerning the rental of the tool.

Further "investigations" have revealed what seems to be some binding as the cam lobe passes over some rocker arms that don't seem to be able to be slightly compressed like the others. I am thinking that these may be in fact seized. I need to get the spring compressor and remove the rocker arms one at a time to isolate the one making the noise associated with the apparent binding. I can then remove the compensating device and check it.

Do you know of a source other than MB for the test guage used to measure the height of the compensating device?? According to the MB manual it would appear that you need to spin the engine to achieve oil pressure before measuring the height- something I can't do with it on an engine stand; I assume you have to wait until the engine is back in the car to check that.

Randy

[ctaylor738]

I know from my experience with my '81 380SL that a noisy valve train can indeed mimic bottom end noise. It looks like you have some bad ball studs. The recommendation that I got was to replace a complete side. You should also replace any worn rockers and (God forbid) camshafts.

I recommend buying one new rocker to use as a check.

When you replace the ball studs, you should also check the preload with the special guage and correct it with the appropriate size thrust washers. Since the preload measurement is against the spring, I don't think it matters if the engine has been rotated. You can get the tool from Assenmacher Specialty Tools in Boulder CO for about $40. Mercedes actually now resells their tool for about the same price.

You may also find that the thrust washers are worn where the rockers contact them. On several of mine, simply replacing a worn thrust washer with a good one of the same size restored the correct pre-load.

You should also be aware that the timing chain makes a huge amount of noise if it is loose and it is difficult to tell it from valve noise.

I will need to talk with Mercedes to compare prices but Assenmacher quoted $88 for the gauge. I really don't know how I could be sure of the setting without one. As I mentioned I was surprised to find the loose rocker arms, I had myself convinced it was bottom end.

I'll keep the worn thrust washer idea in mind when I start looking into the ball stud situation.

It would appear that the chain has about 8 degrees of stretch, and along with a number of other things I plan to replace it , guide rails, and tensioner before reinstalling the engine.

I appreciate the information, thanks.

Randy

[ctaylor738]

I actually bought the guage from American Service Center in Arlington VA for $42. It would have to be the first time a dealer has ever marked DOWN an OEM price.

Just to close the loop:

Herr Fuchs told me that a "good" ball stud should compress "only a little" when the cam lobe is rotated down. You measure this with an educated finger between the lower edge of the rocker and the top of the ball stud flange. Feel it with the cam up, rotate, and then with it down. It should barely change.

Here is my procedure for checking. Work from front to rear in order.

- Turn cam lobe up.

- Check preload with tool. If OK do, nothing.

- If not, remove rocker and valve pad.

- Insert good 5.1mm pad and reinstall rocker arm. Rotate cam lobe 360 deg. Let ball stud compress for 2-3 minutes. Estimate difference you will need to bring into spec, and note corresponding pad to order.

- Repeat for all valves.

- Go to dealer (stock item) or web site to order required pads.

- Install and re-measure as above.

Herr Fuchs also told me that it is extremely unusual to go less than 4.75 or more than 5.45. If need a thicker or thinner pad, something else is wrong.

Once again thanks for the information. This is very interesting. After getting the price from Assenmacher ($88) I called the local (Cincinnati) Mercedes dealer and gave them the part number of the test gauge and they looked it up and said they could order one for $300+. After your last post about getting one from the dealer in Arlington I called them and they said they could order it for me and it would be $57 plus shipping which is fairly reasonable. You can imagine how excited I am about the fact that I may at some point have to walk in the door of the Cincinnati dealership!!

Randy

[brooktre]

Randy,
I didn't see this mentioned, but if your 380 does not have a double row timing chain, you need to upgrade it.

Yes, thank goodness this car passed back through a dealer that did the conversion before it was sold to the previous owner in 1986.

Randy

I purchased the KD 3087 valve compressing tool and it works well. As I mentioned I had two ball studs that were collapsed. After removing the ball studs from the block they both returned to their original height and I was unable to compress them after they did that. The oil passage to both of these ball studs was open as compressed air passed through after pushing out the oil. It's not like this engine was one that didn't get regular service and there is crud in the oil passages- this engine has no build up of any type.

Of the 14 other ball studs I found 2 that would not compress when I applied pressure to the rocker arm on top of it. After rotating the crank ten or twelve revolutions I found several of the ball studs that would initially compress slightly were now rigid. It is difficult to make sense of these things.

Randy

[ctaylor738]

I had the same situation.

I started out with a loud clatter, but no obviously loose rockers and one easy-to-compress ball stud. I did Herr Fuch's finger check and found four with problems. Replaced all ball studs and all worn pads. The clatter went away, and I ended up with several 'tickers.' Did the adjustment with the guage, replacing four 5.1's with 5.45's. Now I think the valves are quiet, but I have some chain noise.

IMHO, you really can't tell from bench testing whether you will get noise when the engine is running. If you have noise, and you cannot find a clear indication of the problem, then I would do all the ball studs, check the condition of the pads, and check the preload with the guage and adjust as needed.

In your case, I would try replacing the two you found collapsed, check all pads for wear, and do the preload check with the guage.

I have decided to replace the two ball studs that were collapsed (until I removed them) as well as one other one that seems particularly "soft". After completing other items on the list of things to do before reinstalling the engine I will get the car running and sorted a bit before doing a complete checking of the ball stud/ rocker arm/thrust pieces.

While chasing the clicking sound I was hearing from the left cam I found that the cam sprocket was loose and had hammered the Woodruf key enough to allow 3-4 degrees of play. This is just a normal key and not one of the ones used to adjust cam timing. I was only able to find the offset keys while online shopping.

I have read a lot on this forum concerning the aging and break down of the material used to make the chain guides and the importance of changing them as they age. I haven't however seen anyone talking about (nor do the achieves contain) any experiences with slide rail failure. The guides on my car look new but the slide rails behind the timing case cover are very dark brown. Obviously these are no picnic to change out because the necessity of removing that timing case cover (and everthing in front of it) complicates things. But if the guides are prone to failure than I would assume that the slide rails are too. Has anyone had any expience with slide rail failure or replacement?? Do I have more important things to worry about than the slide rails??

Randy

Ref: Loose cam sprocket

I found the loose cam sprocket late last night and after having time to think about it went back to investagate this morning. The person who had been looking into this engine noise before me had evidently left of the compensating washer off. This is the washer betyween the sprocket and the front tower on the left cam. No wonder the Woodruff key was hammered. The bolt and washer were not even in contact with the sprocket. All that was preventing the cam sprocket from taking a "spin" on the camshaft was the key. That certainly could not have last very long- I feel like I dodged a very big bullet.

Randy