M276 SLK 350 2011 Startup Rattle

[Winsoxuk]

Morning all hope you are well I've recently purchased a SLK 350 and I'm super happy with it.

One thing I've noticed so is there's a massive rattle at startup so I plan on replacing the chain tensioners with the modified versions the oil valves to prevent drain back and also it sounds like one of the cam adjusters is not locking.

Is there anything specifically I need to keep a lookout for it seems a fairly straightforward job and I've ordered the alignment tools which should be arriving in the next couple of weeks.

Any advice before I start tearing it down would be great, especially if it's worth while replacing other seals whilst it's all got the top off

Many thanks in advance
Dave

 

[TC350]

I have the M276 engine in my 2012 C350 and I first noticed a cold start-up rattle when the car was still under the manufacturer’s warranty. My MB dealership couldn’t find anything wrong. When I mentioned it on this forum I was told that it was a known issue by MB with a known solution. I can’t remember the details but you’ll find them if you search for M276.

I decided, rightly or wrongly, to wait and see what happened over time rather than rushing into repairs/modifications. Several thousand miles later I happened to be standing next to the car‘s front passenger door when my wife started it from cold. My initial reaction was that the rattle came from under the car and not the engine. But when I lifted the bonnet the rattle did sound as though it was coming from the engine. As usual, it soon disappeared so I couldn’t investigate any further.

The next morning, with the car cold, I lay on the ground and got my wife to start the car. The rattle definitely sounded as though it came from around the exhaust system. As best I could, I tried moving the pipe work to see if anything was loose, but all was fine. The car was due a service at MB a couple of weeks later, so I asked them to check the exhaust system while they had the car up on ramps.

The mechanic found a hairline crack about a third of the way along the system. The options were either to replace the system (at great cost) or weld up the crack. MB didn’t do the latter so I took it to a local garage who did the welding for under £100.

The cold start rattle has gone! Presumably the crack closed up when the exhaust heated, but until then escaping gasses shook the surrounds.

There’s still a tiny rattle on cold start, but I can’t hear it from inside the car. This may be the initial lag in oil getting around. It’s certainly nowhere near the rattle of any diesel starting, so I’m not bothered by it.

 

[Winsoxuk]

W276 Start up rattle

Unfortunately mine is definitely coming from the center of the engine and you can hear the rattle from where the cam adjusters are.. I upload a small video.

 

[RichardF]

Before you launch into anything expensive try the simple things 1st.
I had similar, the car was running on ECP own brand oil albeit the correct specification. I swapped to Petronus (other premium brands are available) and all fixed.

 

[Winsoxuk]

Before you launch into anything expensive try the simple things 1st.
I had similar, the car was running on ECP own brand oil albeit the correct specification. I swapped to Petronus (other premium brands are available) and all fixed.

It's been serviced at Mercedes and had the correct oil in it. It also been changed again last week and it's still just as noisy.

Locking timing kit has arrived and also tool to install none return valves so willl throw it all in when chain tensioners and cam adjusters arrive .

 

[Bayleaf]

I had the same issue and looked at fitting new tensioners and the little valves you mention ( I can't remember what they're called off hand ). I even bought the tool to press them in the heads. The main reason I didn't do the job was because I couldn't get definitive explanation from several forums on the timing marks for both heads. However, I started using Shell Helix Ultra engine oil and the problem has gone away.
Hope this is of some help to you.

 

[Winsoxuk]

I had the same issue and looked at fitting new tensioners and the little valves you mention ( I can't remember what they're called off hand ). I even bought the tool to press them in the heads. The main reason I didn't do the job was because I couldn't get definitive explanation from several forums on the timing marks for both heads. However, I started using Shell Helix Ultra engine oil and the problem has gone away.
Hope this is of some help to you.

I'll let you know how I get on. I think I'll do the tensioners and the non-return valves first and see if the rattle goes away. I've got a pretty good video showing what it sounds like when I first start the car cold or when It's been sat with a hot engine for 30 mins. If that does not fix it I'll pull the cam adjusters and see if the locking pins are worn. From what I've seen of the design this is definitely a part that will wear.

I will take some pics and try to explain the timing marking and how to check, you dont want to get that wrong !

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[TC350]

I'll let you know how I get on. I think I'll do the tensioners and the non-return valves first and see if the rattle goes away. I've got a pretty good video showing what it sounds like when I first start the car cold or when It's been sat with a hot engine for 30 mins. If that does not fix it I'll pull the cam adjusters and see if the locking pins are worn. From what I've seen of the design this is definitely a part that will wear.

I will take some pics and try to explain the timing marking and how to check, you dont want to get that wrong !

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That’s a proper rattle, far worse than what I experienced. I hope you get it sorted.

 

[Bayleaf]

Yes, I agree mine didn't sound that loud, however if that video was done in an enclosed place e.g. garage you can get an echoing effect.
I've just noticed Winsoxuk that your car is a 2011 model and I didn't think the 276 engines came out till 2012 The earlier 350 V6 which if I'm not mistaken was the 273 engine had problems with a balance shaft sprocket that was fitted to that engine resulting in noise coming from the center of the engine as you describe.

 

[TC350]

Yes, I agree mine didn't sound that loud, however if that video was done in an enclosed place e.g. garage you can get an echoing effect.
I've just noticed Winsoxuk that your car is a 2011 model and I didn't think the 276 engines came out till 2012 The earlier 350 V6 which if I'm not mistaken was the 273 engine had problems with a balance shaft sprocket that was fitted to that engine resulting in noise coming from the center of the engine as you describe.

The M276 engine was introduced in late 2010. I ordered my C350 with it in 2011 (although it wasn't delivered until 2012)
M276 3.0/3.5L Engine - In-Depth Look at Design and Reliability

 

[BlackC55]

Before you do anything check the timing. I have not yet successfully fixed and engine rattle with a new tensioner. Its often a waste of time.

Check the timing and if its out replace the chain and tensioners and I would certainly fit new adjusters at the same time.

 

[Winsoxuk]

Yes, I agree mine didn't sound that loud, however if that video was done in an enclosed place e.g. garage you can get an echoing effect.
I've just noticed Winsoxuk that your car is a 2011 model and I didn't think the 276 engines came out till 2012 The earlier 350 V6 which if I'm not mistaken was the 273 engine had problems with a balance shaft sprocket that was fitted to that engine resulting in noise coming from the center of the engine as you describe.

Its a 276.956 30015207 as i check this before I bought it,

 

[Winsoxuk]

Before you do anything check the timing. I have not yet successfully fixed and engine rattle with a new tensioner. Its often a waste of time.

Check the timing and if its out replace the chain and tensioners and I would certainly fit new adjusters at the same time.

I totally agree ,.. the tensioner and check valve update would only fix minor rattles.... mine very loud and id put money on one of the Cam Adjusters.

 

[Winsoxuk]

That’s a proper rattle, far worse than what I experienced. I hope you get it sorted.

This was my 850R when I bent a rod, now thats a nasty noise !

Volvo 850R Before & After Rebuild

 

[Winsoxuk]

Spent 1 hour on it last night, chain tensioners not been replaced with improved version and oil valves not fitted. I've ordered them and will fit first...if that don't fix it I'm ordering cam adjusters.

As per mod instructions I have the 8mm hole

On another note anyone know the torque settings for the chain tensioner bolts ?

Click on pictures link if anyone is interested..I'll update as I go along

Cheers all !

Got to say a lot easier to work on than the Audi I had !


Pictures

 

[TC350]

Well done for taking it on. It’s very many years since I tackled a car engine.

 

[Winsoxuk]

I've also found out that the electro magnets that control the cams are leaking it looks like the o rings have failed have managed to find a manufacturer of them.

Outside Diameter 60mm Inside diameter 50mm Diameter of the actual ring 2.5mm

 

[Bayleaf]

Spent 1 hour on it last night, chain tensioners not been replaced with improved version and oil valves not fitted. I've ordered them and will fit first...if that don't fix it I'm ordering cam adjusters.

As per mod instructions I have the 8mm hole

On another note anyone know the torque settings for the chain tensioner bolts ?

Click on pictures link if anyone is interested..I'll update as I go along

Cheers all !

Got to say a lot easier to work on than the Audi I had !


Pictures

Did you time the engine up or did you just remove the tensioners. The reason I ask this is that I read somewhere that it didn't have to be timed up as the sprockets don't move when the tensioner is removed. Also if you google the problem there are a couple of vids on YouTube on how to do the job but they only show doing it on one head.

 

[Bayleaf]

I've also found out that the electro magnets that control the cams are leaking it looks like the o rings have failed have managed to find a manufacturer of them.

Outside Diameter 60mm Inside diameter 50mm Diameter of the actual ring 2.5mm

You might want to check your cam shaft position sensors as they can leak oil internally and transmit it into the main loom. I changed all mine last year for updated ones.
The VVT ones were not affected. However as a matter of course I check them all once a year when servicing. Again there are vids on YouTube.

 

[Winsoxuk]

You might want to check your cam shaft position sensors as they can leak oil internally and transmit it into the main loom. I changed all mine last year for updated ones.
The VVT ones were not affected. However as a matter of course I check them all once a year when servicing. Again there are vids on YouTube.

Yes thank you for the advice I've actually checked these and they're not leaking.. I suppose it's only a matter of time before decided piss out oil. Lol