Process for replacing rocker arm and ball stud assembly
 

My questions relate to a 420 SEL, 1986, Engine 116.
Due to a loud ticking noise coming from the valve cover, in the area of the #1 cylinder, I plan to remove a couple of rocker arms to inspect for wear. In researching this subject in the shop forum archives, it's unclear if the use of compressed air is required to hold the valves closed while this work is being performed. Some posts make mention of it and others do not. If compressed air is required, I'd like to know "how much pressure"?

Another question? Just based on the noise, can anyone tell me how to differentiate from the sound of a rocker arm gone bad versus a failed rocker arm and ball stud assembly?

Thanks for any response.

William

Compressed air
 

No compressed air is required. Just rotate the cam, by using the starter, or by wrench.

As you probably already know, the cam shaft could also be worn.

Thanks for your response. One of my problems is that I don't know how to assess wear on a cam lobe and hopefully you can help me with this.

In searching the shop forum archives, it appears that the Mercedes shop procedure is to automatically replace the cam shaft, all rocker arms and all lash compensators. This is great, but obviously very costly. On the other hand, a Mercedes technician posted a discussion on the subject in which he said that in the field the cam shaft wasn't replaced unless there was evidence of wear on the suspected cam lobe, and only the suspected rocker arm was renewed. I couldn't find anything that gave instructions on how to assess wear on a cam lobe.

I have removed the valve cover on the side of the engine that is noisy and checked the cam lobes for any sign of roughness and they're all smooth. On the other hand, it's my understanding that you can't reach a conclusion without first removing the rocker arms.

If you want to be really sure about the lobes, you can put a micrometer on them from bottom to top and check for consistency.

I checked my rockers by buying a new one and checking the profile of the old ones against it. You may aslo find that the "hockey puck" shims are worn from contact with the rocker arm, or that the rockers have a lot of wear where they rest on the ball stud. Either condition will cause noise.

Sometimes a new puck of the same size, or one size thicker will eliminate the noise.

There ain't a great way to check the ball studs. If you can move them by pushing on the rocker with a hammer handle with the valve closed, then they need replaced. If you can feel a large difference in where the rocker sits with the valve closed vs open (Herr Fuch's finger check), then replace.

And certainly replace the plastic pieces on the oil tubes while you are in there.

Many thanks to you, Chuck Taylor. In several reviews of the ShopForum archives, on this subject, I came across a number of your "posts" and each one was informative and helpful. Your contributions to this forum are greatly appreciated.