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

[cornblatt]

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!