Update
 

Well, I found this thread, which seems to match my noise exactly.

Still a bit of trouble shooting to do, but I suspect strongly that I have hydraulic lifter noise. I have to pull the valve cover to check timing chain stretch, anyhoo, so will check lifters/cam at the same time.

Now, the big question, what is the root cause of the lifter wear, if it turns out to be lifter wear?

I'm starting to lean towards the idea that jltcasper3 brought up. Might just be the head gasket beginning to fail and obstructing oil passage/passages.

There is a bunch of stuff I plan on doing anyway (fuel filter, coolant flush, another oil change, probably will do the pressure-wastegate mod, thermostat, preventative vacuum pump renewal), so I think I may just pull the head and change the gasket as a preventative, as it does leak a bit of oil, and it seems gaskets on this vintage of M-B are sort of notorious for ****ting the bed at regular intervals (I had a '93 190E that needed a new head gasket about every 60k).

Will photograph stuff and report any findings.

Something else to check: inspect the camshaft, gear, and timing chain carefully. There was another case of a camshaft key missing that allowed the camshaft to float fore and aft, with some weird noise I think.

Wouldn't a compression check reveal if weak / oil starved lifters were not fully opening and allowing full compression?

Pulling the head just to diagnose a noise is a bit extreme.

Pulled the Valve Cover
 

... and checked timing chain stretch. That can be a little nitpicky. Thanks to good help from threads here, I figured it out, and discovered that I only have about 1.5-2.0 degrees of stretch. Seems fine there.

Warmed the engine and then turned through per FSM procedure to check hydraulic valve actuators. 5 of the 10 showed noticeable movement/drop. So it now sounds like I have to inspect passages feeding the hydraulic actuators for contamination. And I guess replace the actuators while I'm at it. So off comes the cam soon. Lobes seem fine, with what I'd consider normal wear for a 130k car. No gouging, grooves, or oddly uneven wear that I could see.

I think I read somewhere that there is a plug on the rear of the head you can pull and then blow compressed air through the passages feeding the valve actuators in order to clear them. Will have to search for that again- unless anyone knows off hand where to find it.

Unfortunately, from what I read here, I may have a failing head gasket, as noted in previous posts. What else could clog up those actuator galleries?

Additionally, I noted a good bit of blowby while running the engine (had the breather pipe disconnected during warmup) and there is a noticeable flow of crankcase gasses under pressure coming from the breather. That's a little off-putting. How much is normal?

Which hydraulic actuators were weak? If the back cylinders, than yes I would also lean toward a clogged oil passage. If they are random, then maybe not.

When I installed a head on my OM603, I left the camshaft off, and all of the hydraulic actuators removed. I suspended the timing chain on the camshaft gear with a 1/2 inch drive extension (or maybe it was 3/8?). I think all the injectors were also out, so no compression. I stuffed a rag at the first camshaft bearing oil feed under the drive extension to block that oil "leak", and then used the starter to rotate the engine and pressurize the oil galleries. After a good few seconds of flow at each hydraulic actuator hole, I installed them from #1 to #6, waiting at each hole for pressure to build and oil to flow so that I could verify good flow and flush out the oil passages.

You could do something like that to check the flow / pressure at each hole.

It is also possible to take apart and clean the hydraulic actuators, and avoid the expense of purchasing new. Number them by location so you can put them back in their original holes.

If your blowby is severe and random actuators are flat, that may point to poor maintenance - too long between oil changes - which leads me to believe that carbon clogging of the rings and the actuators is the issue, NOT a failed head gasket.

In answer to your question regarding blowing compressed air through the plug at the rear of the head to clear the oil passages yes it can be seen in the picture of this link.

https://www.google.ca/search?q=mercedes+602+head+pictures&prmd=isvn&tbm=isch&tbo=u&source=univ&fir=4QUMuIoih6_hMM%253A%252 CVlKZNX3xCS-6uM%252C_%253BAJedEYW4ggObPM%253A%252CVlKZNX3xCS-6uM%252C_%253BMcbEYWUYFrKHDM%253A%252CrdU5ywV_12JHAM%252C_%253BmwO_VWaAvDT_4M%253A%252CH_oc5Pcvae-c3M%252C_%253B7FCw3oCTSaWUuM%253A%252CbsZTnJ0CCY6o1M%252C_%253BEr-Cx_BYV3M2UM%253A%252C8ijr1iYSKH8WkM%252C_%253BcxGWnCrIiNxGmM%253A%252CxvhEBki8hPZPtM%252C_%253BnoOVJ v_CMB_FeM%253A%252CabQb3Srs0y6KqM%252C_%253BTnAXtd1bdDXxqM%253A%252Ckykl1XjALW3iUM%252C_%253B2Jwy8kV BBJ-qsM%253A%252CxvhEBki8hPZPtM%252C_%253B9P3NwHtuCjpJaM%253A%252C4jUgwTeLCp_-4M%252C_%253BbgSGq7c9tXHr4M%253A%252CIPn8bsihCZEcpM%252C_&usg=__YNi0Edk9WSfiyy9lYkVXyhRn3HI%3D&sa=X& ved=0ahUKEwj8iJOOle_SAhVE-mMKHTjVAAMQ7AkINg&biw=589&bih=371#imgrc=C6C2Hzj7o9snnM:

I believe the head needs to be removed limited room to acess the plug and the cam also needs to be removed to allow any contamination to fllow out.

Maybe time for a compression and leak down tests.

Collapsed hydraulic lifters are fairly common. Before pulling the head and putting at ton of extra work into this engine that you don't need to, try disassembling them and simply cleaning them. Keep them marked which positions they go back into so you don't ruin your cam.

While it's all out, the port to blow out the oil galleries is in the rear corner on the driver's side. I believe it's an 8mm bolt point directly back at the firewall. Very limited clearance. On my 603 (with 12 collapsed lifters) nothing but air came out of any of the oiling ports when I pressurized that passage. The lifters WERE full of varnish and muck though. Cleaned them out and have several thousand miles on them and they're all silent.

ALL diesel engines have blowby (all engines in general have blowby, but diesels have a bit more than their gasoline counterparts). The higher the compression and the higher the miles (or wear), the more they have. With the engine hot and at operating temperature, the general "test" is to loosen the oil filler cap and let it sit on the filler hole. If it's bouncing you have excessive blowby (not to say it's time to rebuild the engine just yet). If it blows off the hole or is dancing around on the valve cover, it's just about time to do a rebuild.

ticking noise OM602 engine
 

have also a W124.128 with about 135K. Engine made the same or a very similar noise at idle. Timing chain was changed when cyl.head gasket was replaced and I also installed the upgraded vac. pump. Therefore I also suspected the hyd. lifters. Stetoscope confirmed noise was coming from the top, middle of the engine. Bought new lifters but did not fancy the job and they are still in my basement. Switched engine oil to Shell Rottela T6 and after driving a couple of thousand miles ticking disappeared. Just my experience.
Did use 15-40W regular Rottela before with shorter than recommended oil change intervals.
Cheers

Ordering/numbering the 10 actuators from front to rear they were: 1, 3, 7, 8, a teeny little wiggle on 9, and 10. 10 was the worst of the bunch.


Saw some info on that. May give it a whirl. Cost isn't too much of a factor, though, and using new may save time. I'm on the fence.

That's certainly good news. 2nd owner didn't change oil as regularly as the first. But then again the car was only driven ~7k miles over a period of about 10 years by the second owner. It seems to have sat quite a bit, which isn't good either. On that note- what's a good way to try to clear possibly-stuck rings? I'm in agreement that a compression/leakdown test may be required soon.

Perfect, thanks. Fortunately, front and rear clearance with the 5-cyl engine is pretty darned good. I think I can reach that plug without much issue, hopefully.

So, stupid question time: Would that quick test be performed with all the breather apparatus still connected (breather tube still feeding the turbo inlet)? Or would I need to remove/block the tube for a correct assessment? With everything connected, I can observe blowby gasses when I peek into the valve cover, but the pressure doesn't seem to be enough to push the oil filler cap around when it's just loose in the hole. When I had the tube disconnected from the turbo inlet and briefly plugged it with my finger, there was definitely enough pressure to immediately push the cap off the hole.

The breather tube should still be connected when checking for blowby pressure. There will ALWAYS be positive blowby pressure in the crankcase, so if you block the breather, you will pressurize the crankcase (these cars don't have a flow-through PCV system like the gas engines).

My SDL has enough blowby to fill the valve cover with mist/smoke, but not enough to move the cap.

If you car sat a lot, you may have varnish/sludge issues on top of what you already know about with the car. I certainly had some NASTY garbage come out of my engine (sat for 10 years in a field). Oil filter housing was full of something akin to pie filling, bottom of the sump had something similar to jello in it. Nasty, nasty, nasty. After 3 oil changes and an engine "flush", the oil is back to being oil again and the engine is much happier. Oil consumption went from 1.5 quarts every 500 miles to less than 1/2 quart ever 2000 miles and still improving.

I'd suggest just cleaning out the lifters you have (you may be surprised [and repulsed] by what you find in there [the smell is truly appalling]) and running synthetic oil for a couple of short-duration oil changes to clean out all the "crap" that's likely collected in there.

Easy: Switch to Mobil 1 synthetic oil, give it some time to clean up the carbon (thousands of miles).

A little harder: fill each cylinder with Marvel Mystery Oil, let that soak for at least a day, change oil before driving.

Compression tests before and after may help confirm that you're making progress.

Personally, I just use the M1 oil and stop worrying about it.

any update?

As for me mine did this tick, especially after a hot freeway drive, and then sitting in a drive-through. When I got around to it, I adjusted the "too soft of a shift(s)" at my transmission modulator due to flaring, and not only did the shifts tighten up, but the throttle response and the tick disappeared to. It's almost as if when you have a vacuum source hogging the pressure, that it makes other things go weird as they are all tied in somehow.

Freak thing, not sure if coincidence, but that's a lot of symptoms to go away suddenly.