Is A Valve Adjustment Needed?
 

I have a Mercedes Benz 1989,with a non turbo 2.5,,,the valves are "TICKING" every once in a while,not all the time,if I reve the engine the TICKING stops then comes back or not,I also noticed a puff of black smoke at cold start up and smoking under hard excelleration.I took it to a mercedes mechanic and he told me this engine has hydralic valves and they are self adjusting.Is this so?What could cause the smoking?Do I need to look for another mechanic?The car has 300,000KM on the clock.

Ticking valves is a common occurrence on the engines with self adjusting hydraulic valves...its age related, but will not cause any problems. You can ignore it, or try running a synthetic oil like Mobil 1 turbo diesel oil. Some have reported the ticking going away with synthetic diesel oil. Otherwise don't worry about it.

What would cause the smoking

What color is the smoke?

Smoke is black,car does not burn oil.

Black is either too much fuel or too little air. Check the air filter

You car does not have manually adjustable valves.

Check for a sticky EGR, and also have the injectors checked for pop pressure and spray. A leaky injector, or late injector can cause this. Also check your glowplugs. A cold cylinder can cause this when cold.

Also, prechambers missing the "balls" can
also cause this.

Self adjusting valves are the way to go.

I wonder why I've never heard any complaints about the OM606 having ticking lifters. Did MB finally fix this issue with that engine?