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Hello, I do have cold start rattle for last 8-10 months a bit more pronounced on bank 1 (passanger side Europe/US side) also (11months ago i have changed as preventive my chain tensioners on bank 1 and 2), which during that time i had driven the car everyday (15k km + -), in the meantime i have tried to find what is the issue without pulling engine out and checked if VVT jumping during manual rotating the engine but doesn't, no errors during that period of time related to timing etc.
as side info: my oil pump solenoid + alternator are unplugged
today i had call from a garage that the sound is from bottom front which leads to oil pump area (main chain) below i will post a video of the sound
What a perfect video research @atomek brings us. It goes through tensioner failures.
I had observed this defect on my genuine NIB units but had not "connected the dots" to conclude new MB tensioners were already defective in the box.
New tensioners can jam in fully retracted position thereby causing loose chain slap rattling.
@KristiyanPetrov
90% chance this is the issue with your already new tensioners. Notice how your rattling is a little bit delayed after starting.
These M276/8 genuine MB hydraulic tensioners have more than one way to require repairs:
-1 - Their oil seal can drain standing oil overnight and drop pressure much needed by the VVT Phasers.
-2 - The video shows evidence of the plunger shaft getting stuck and not releasing from storage location.
I have seen this shaft jamming in my hands with my own eyes. This new-tensioner defect is not anecdotal legend from a small batch.
This is the official "tensioner-rattle" from genuine new or original old parts.
-3 - Personally I can add the backing surface is not to be trusted as smooth ready to mate with engine surface.
My NIB genuine MB tensioner had a half milimeter (1/2 mm) metal defect sticking out that would have caused significant pressure lose (not speaking of course milling machine marks).
Normally I would trust these secondary tensioner to be spent near 100k mark but now we recognize they can fail a lot earlier.
The camshafts positioning is extremely sensitive to enable or disable basic GDI engine timings + performance. Stable Cam timings are as important as reliable sparks ("under-gapped") for engine timings else lean mixtures are misfired.
New tensioners around 75kMi is good DIY care.
Unfortunately checking on tensioners requires upper timing cover removal.... migh as well change unit like in the video for 3rd time.
HPFP may have a role to play in compressing down tensioner while engine is off without oil pressure. Turbo cam has 4-lobes, right?
You may want to go inspect/replace HPFP ROLLER-follower before it can eat into the intake camshaft. Then that means... recommended PCV + HPFP jobs or keep for later.
My opinions .... see notes.
Last edited by CaliBenzDriver; Oct 23, 2025 at 08:36 PM.
What a perfect video research @atomek brings us. It goes through tensioner failures.
I had observed this defect on my genuine NIB units but had not "connected the dots" to conclude new MB tensioners were already defective in the box.
New tensioners can jam in fully retracted position thereby causing loose chain slap rattling.
@KristiyanPetrov
90% chance this is the issue with your already new tensioners. Notice how your rattling is a little bit delayed after starting.
These M276/8 genuine MB hydraulic tensioners have more than one way to require repairs:
-1 - Their oil seal can drain standing oil overnight and drop pressure much needed by the VVT Phasers.
-2 - The video shows evidence of the plunger shaft getting stuck and not releasing from storage location.
I have seen this shaft jamming in my hands with my own eyes. This new-tensioner defect is not anecdotal legend from a small batch.
This is the official "tensioner-rattle" from genuine new or original old parts.
-3 - Personally I can add the backing surface is not to be trusted as smooth ready to mate with engine surface.
My NIB genuine MB tensioner had a half milimeter (1/2 mm) metal defect sticking out that would have caused significant pressure lose (not speaking of course milling machine marks).
Normally I would trust these secondary tensioner to be spent near 100k mark but now we recognize they can fail a lot earlier.
The camshafts positioning is extremely sensitive to enable or disable basic GDI engine timings + performance. Stable Cam timings are as important as reliable sparks ("under-gapped") for engine timings else lean mixtures are misfired.
New tensioners around 75kMi is good DIY care.
Unfortunately checking on tensioners requires upper timing cover removal.... migh as well change unit like in the video for 3rd time.
HPFP may have a role to play in compressing down tensioner while engine is off without oil pressure. Turbo cam has 4-lobes, right?
You may want to go inspect/replace HPFP ROLLER-follower before it can eat into the intake camshaft. Then that means... recommended PCV + HPFP jobs or keep for later.
My opinions .... see notes.
if chain tensioners are defective from factory, then i don't know what anymore to say... honestly so disappointed
It’s worth noting, defect rate for genuine MB valvetrain parts like this is something in the 100-150 parts per million range. You guys can do the math on that as a percentage. Needless to say, it’s very low…
(.015%). Q.C. on valvetrain parts is pretty tight.
If I was a betting man….
Good Luck Keep us posted.
Last edited by crconsulting; Oct 25, 2025 at 08:49 AM.
That youtuber with the c43 did a tear down of his faulty part. He didn't conclude anything other than taking a look inside to see if anything stands out.
Great job finding this gem video!
Now we can peek inside these HYDRAULIC RATCHETING tensioners for more educated opinions - Thank you @atomek I had been puzzled for a while myself.
Chain tensioners are maintenance parts to keep in perfect condition else unexplained MISFIRES develop.
Internal components...
The cutaway parts reveals internal components that support misc functions:
Long coil spring
Small oil check-valve
Ratcheting ring + grooves
Seal plunger to bore
Air/Pressure relief holes
The tensioner has two relief bleed holes for air & lower start stress when not held by oil. Air is compressible and must be discharged after each start.
> LONG STORY SHORT:
-- Tensioners need working oil pressure to become effective.
-- Ratcheting *helps* control the chain slack even under low-pressure conditions.
-- Defective tensioners are unable to hold chain slack.
> IT IS WHAT IT IS:
These units have the proven ability to rattle and get stuck retracted.
Limited oil pressure doesn't guarantee ratchet extension. Stuck-tensioner rattling is the call for action.
The guy in your video with a collection of multiple low-mileage genuine tensioners likely suffers from ineffective oil pressure. Meaning not enough pressure to deploy shaft plus not enough to hold back the chain guide.
> UNKNOWN CAUSES...
I will not visiting the multiple factors for tensioner failures.
ratchet grooves look smoth
Suggested replacement around 75k.Mi depending on conditions.
> HYDRAULIC ASSIST FORCES...
We've seen the oil pressure is what make these tensioners work or not work.
What range of forces are at play?
Let's say we have
shaft diameter of 1Cm
working oil pressure: 20Psi Min.
working oil pressure : 60Psi Max.
Hydraulic forces range from:
2.5Lbs Min
7Lbs Max
Static spring force: 50.Newtons or 10.Lbs.
I find that the spring force is greater than that of the Max oil pressure. In other words, the oil pressure is less significant than coil spring besides oil is not compressible unlike spring.
Oil pressure above losses (bleeder + seal) hold back tensioner plunger.
These secondary tensioners are low forces. They are not in the business of creating extra frictions but hold still to prevent loose timings.
Seasoned tensioners must go!
Last edited by CaliBenzDriver; Nov 8, 2025 at 06:31 AM.
Hydraulic secondary tensioner
