Hydraulic lifter check - is this one bad? (video)
 

I have a 1984 190D-2.2 (with the 4-cylinder OM601 engine). Someone else with a 190D just moved in down the street from me, and I noticed how quiet their car is compared to mine.

Since then, I've been trying to track down a tapping/ticking noise coming from the engine. The forum searches I did seemed to say that the most likely source was an injection problem or hydraulic lifters.

I did the loosen-the-injector-lines-and-see-if-the-noise-goes-away thing. It didn't.

So, I thought I'd check the hydraulic lifters (a.k.a. cam followers a.k.a tappets) to see if they were misbehaving.

The FSM says:

1. Run engine for approx. 5 minutes at 3000/min.
2. Remove cylinder head cover.
3. Set cam of respective valve tappet on base circle (cam tip should point upwards).
4. Use a mandrel to push against valve tappet or try to move valve tappet manually. If, compared with others, the valve tappet drops quickly, or in the event of play in relation to base circle of cam, perform jobs item 6 and starting item 8 (i.e. investigate further)

Reading this, I thought I'd be able to depress them all manually and some would depress more easily than others. However, this was not the case. In general, they were rock-solid and could be rotated but definitely not moved vertically. Only one moved a visible amount. I could feel very very minimal movement in three others but it was so small it was not visible to the eye.

Here's a video clip of the one that moved the most. It only moves about 1mm (<1/16") and then it's solid. Could someone who has checked their lifters before (and found bad ones) please let me know if this constitutes a defective lifter? I kind of expected more movement based on the text of the FSM. Would this amount of movement in the lifter be a source of noise?

http://www.youtube.com/watch?v=k33tqR_F8ko

I've also attached an image of the engine showing the location of the video clip so that you know what you're looking at!

Thanks! :)

If you are cam point up there might be a chance you're opening the valve and touching the piston crown. If you're only using finger pressure my guess it is a soft/collapsed lifter.
When you mention the noise, have you used a stethoscope (or screwdriver handle to the ear) to try and isolate it?

[quote]If, compared with others, the valve tappet drops quickly[quote]

This would seem to be the case. To be sure, run the engine again and remove the cover to ensure that this lifter is on the base circle and try to press it down. If not, recover it and run it again. It should be solid against the base circle when the engine comes to a stop.

I checked the service records, and the previous owner had the lifters replaced in 1991 at 65k miles and again in 1993 at 85k miles. So, the ones in the car right now are 14 years / 150k miles old. How long do these things usually last?