Hey, any of you people out there who have experienced the low oil pressure issue that occurs when a plastic oil pressure plug "pops out" of the oil pump chain tensioner assembly, I have warnings for you.
This happened to my daughter's car, and we have no idea at what point in time that it occurred. We continued to drive it and service it normally as if all was well. While we were happily driving it around, we were completely unaware that a plastic plug had popped out of the tensioner assembly and it was "venting" pressurized oil back into the oil pan resulting in there being a starvation of oil to the top end of the motor and to many of the moving parts. Eventually, at around 80,000 miles, the timing chain had stretched to the point that it simply jumped off the sprockets at a stoplight and the engine died and would not restart.

I searched forums and the web and discovered that these engines had a sort of recall for the VVT cam sprockets. I contacted the dealer where my daughter was located (Virginia, 800 miles from home) and they towed the car and they verified that the car qualified for the "free updated sprockets". I thought the saga was over. A few days later they told me that the timing chain had jumped off of the sprockets, which is NOT a symptom of the VVT sprocket issue and that no "free work" was in the cards. At this point they recommended an eingine replacement at $13,000. I borrowed a car hauler trailer and hooked to my truck and went to Virginia to drag the car back home to Tennessee.

When I got it home, I pulled it apart for inspection. The cam box and head were DARK with varnish. Since we always were prompt on oil change intervals, I recognized that this discoloration was not normal. The entire inside of the upper portions of the engine were discolored. The oil in the sump was fresh and honey colored as I would expect.

When I closely inspected the large plastic lower tensioner block, I saw that a passage plug was missing from the tensioner. This plug was intended to block off a pressurized oil passage. It appears this one had not been glued in adequately. It was at this time that I realized that the excessive cam chain stretch, as well as the discolored inside varnish, that the little motor had been suffering with low oil pressure and flow to the top end while most of the oil had been spewing out of the hole vacated by the plastic pressure plug.

i took a bunch of photos and sent them to the local dealer, the Virginia dealer, and a contact at MB Customer Satisfaction.
"Nobody had ever heard of this issue before" which means that there was no sympathetic ear to be found.

So I took a look around the web and discovered on this forum that there were others who had suffered this same issue. They had linked it to a "loose timing chain sound" when the car returned to idle at traffic stops, etc. My C250 had been driven expressly by a teenaged college girl with her music playing all the time and no "ear" for mechanical discord. So I was never notified of ANY different NOISE coming from the car until the timing chain flopped completely off the sprockets.

I decided that I would do a leak-down test on the little motor and see if it had any bent valves or excessive leakage.
I slowly turned the engine to 90 degrees from TDC to position all pistons at the halfway point. i did not feel any contact (thankfully),.
I used my bore camera to inspect the valves and combustion chambers and found no evidence of hard impact with the valves.
All pistons looked fine, there were no "spank marks" on them.
So I turned the cam so that the valves were closed on #1 and did a leakdown, and repeated that for each cylinder. Leakdown numbers were 9 to 12 psi. This is WELL WITHINI an acceptable range for an 80,000 mile motor.

So I decided that the bottom end and pistons and heads were "good to go" and I fitted the motor with all new timing components. I took the new lower tensioner and installed a small cotter pin in the pressure plug to ensure that it would not happen again.
I then reassembled and retimed the motor. It is a frustrating job to do with the motor still in the car, but far from impossible. I removed the oil pan (by lifting the motor high off of the mounts) and cleaned it out but never did FIND the missing pressure plug. I looked hard for it since some others on the forum HAD found the missing plug in their pans.

I reassembled the motor and drove the car.
I noticed a noise like "piston slap" that I could repeatedly make happen as the motor transitioned from "under load" to :"coast". I kicked myself in the butt for spending so much time on a motor that had possible bottom-end issues, but again, how was I supposed to know?
I took my daughter and wife for a ride and showed them the noise. They both said that they were almost SURE that the car had been "doing that" for as long as they could remember.
So I figured - well, if it is piston slap, maybe it was due to the "farthest" piston oiler jet being weak. And would get worse before there was any worry. If it was a wrist pin, it would be for the same reason and would definitely get worse pretty quickly. It didn't SOUND like it was anything other than those two things,but let's also remember that it is a noise that is difficult to recreate unless it is being driven. I was fairly sure that if it were a conrod, that I could make it happen in neutral and start disabling coils until the bad hole was found.

At any rate, I elected to have them drive it. I offered to put daughter into my truck while I drove her car for a couple of months, but that was not received with happiness. So off it went back to college in Virginia.

It made it 5 months. The last week was accompanied by my daughter telling me that it was running great, but that it was kicking off an ECU code that corresponded to a knock detected. I told her that this code was likely tied to "the noise" and to let me know if the noise was getting either louder or more frequent. She said "it's the same...."

And this went on until I got the next call.
IT'S MAKING A NOISE.
Over the phone (an admittedly poor method of diagnosing audibly thru) it sounded like it punched a rod thru the block. I told her to abandon it in the nearest parking lot. Between herself and her mother, THEY decided that she was close enough to her apartment to drive it back there. The little car somehow made it the half mile to her apartment.

Once again, I pulled a car hauler trailer to Virginia.
This time the diagnostics began with the bore camera.
Four cylinders that look darn nice.
Four sets of valves that look darn nice.
Four undamaged pistons.
No coolant pouring into the cylinders.
All pistons move when the crank is turned.
CRAP, this may not be all that bad.

Out comes the motor.
Apart comes the motor.
#4 Con Rod bearing is in pieces, the rod journal is wallowed out, the crank pin is gnawed down in size.
Hmm - I guess it was never "piston slap".

Let's order a crap ton of parts.
Used standard sized crank, sent to the race shop for polishing - check.
New connecting rod - check.
Deck the block, clean the block, hone the block - check.

Now I am putting this thing back together and taking a hard look at all of the parts.
Guess what - the motor ran long enough with low oil pressure to have starved the cam bearings and cam journals. The "cam box" is gnawed up pretty good. The cam journals themselves are gnawed up some, even though it is "hardened steel on aluminum".

So I'm gonna try out a Chinese cam box. Maybe I shouldn't, but a MB cam box is $730 delivered, and the aftermarket one is $250. And lets face it, the scale of costs is oppressive by now. Actually running out of coin.
Guess I'm gonna chuck up the cams in the lathe and polish the journals. The lobes look fine, having roller tappets on them.

So WHERE am I going with this?
If you are dumping money into one of these M271.860 motors, if it has suffered low running oil pressure, you might want to just find a good used motor, check it to make sure it still has the pressure plug intact, pull the cam cover and make sure it doesn't have "heat varnish" all on the cam boxes.

Mercedes refuses to acknowledge the pressure plug issue. But buyers need to be aware of this when inspecting used motors.

I know that before I became made aware of all of this, I would have "jumped all over" a used 80,000 mile motor for a C250. I wouldn't have even bothered checking for the issues mentioned. I would have done a leak down and then bought it.

That's enough venting for the day.
Mcollins

I think there’s one thread in this forum with your oil plug failure. I couldn’t find it quickly so it must be pretty far back. I don’t think it’s very common, though. We had M271 cars and the dominant early failure was the camshaft adjusters. Some users are recommending timing chain checks or replacement around 100k miles, too.

Sir, I am dealing with the same problem, plug is off and it makes sound when engine is hot.. In my country labor is very expensive but I did some expensive maintainance on my car already so I do not want so sell it :/ I am continueing to drive my car with this problem and I’m scared. Is there any way to change this tensioner withound removing or inclining the engine? Locals shops are saying they must remove the engine for this.. My car also makes some noise like slapping pistons for two years at first few minutes of drive but it goes away after 3 minutes of driving. Sometimes I push the limits of the engine really hard but noise did not increased yet so what do you think? Is it normal to get that little slap sound for 2 minutes or can it be bearings? Sorry for my english and thank you

I wish I had good news for you.
There is cumulative damage to the engine that results from oil starvation due to the missing tensioner plug. Cam journals wear, both in the cams and on the carrier assembly. Piston slap is never a good sound, but if it quiets down after warming up it is not a problem by itself.

You CAN change out the lower tensioner without removing the engine, but it is a terrible and labor intensive job. Borderline "miserable".

If I had it to do all over again, I would have bought a used engine with less than 120k MILES that still retained the oil plug. So the cam adjuster updates and new timing set. Throw on a fresh oil pump, and install it.

I would not have jumped thru all the hoops to try to extend the life of an "already damaged" engine.

Best of luck, friend.

Thank you for your recommendations, I want to ask you what was the viscosity of oil that you were using before the journal bearing failure.
On the other hand 120k miles is not below the safe limit, my tensioner plug came losse around 90k miles :/

Oil was 5W-30.