Chris1979

what if it's just the belt tensioner causing the rattle upon startup!

GLKwanter

I have the benefit of being here and that would be pretty easy to identify standing in front of the engine and cold starting it. It's not external, it's internal.

GLKwanter

This is all very interesting information, and I've considered there being other possible vacuum issues given that there is a little extra oil around the manifold, but the starvation happens after the engine is shut off. Vacuums not continuing to suck oil down for 20 minutes after the vehicle shut off. Turning it off and back on is not going to give you the noise. You got to wait a half hour till the oil leaves the chat.

GLKwanter

I said milage in first post. Look up the startup rattle bulletin if you care, it's common even earlier.

GLKwanter

Today's start up after sitting all night, and the second start is after sitting for an hour+ after the first start.
https://youtube.com/shorts/V_bSbfl2zBQ?feature=share
Maybe it's not the chain but it surely seems oil deprived related.

Odd Piggy

Our GLK350 went 155k+ miles and never had a noise like this. But if it’s not the timing chain, it’s some other rotating part looking for oil pressure. It gets happy when the oil gets there.

There is no balance shaft on the M276, so it’s not that issue. To me it does not sound like valve train noise, but a mechanic’s stethoscope might rule that out.

That M276 sounds uncharacteristically noisy. Everything mechanical can be heard in the videos. Ours was nearly silent even at 150k miles — the only under hood sound was a slight melodic pinging from the valve train. Rather than the 0W-40 I recommended earlier, I wonder if this one might be a candidate for 15W-50.

GLKwanter

Yaaa knoooooow...
I'm in the desert too, 110 out today. I too considered 15w50 after ditching the 0w40, after seeing a coating on the manifold gaskets. Not sure how much is suppose to be there.
Here's a video of that, and inside bank 2, and of pretty good timing from what I can see, bank 2.
https://youtube.com/shorts/qJycKGl8qK0?feature=share

Those recording are in my closed garage, I wanna say it's quiet when driving. Gets 19 city 25 highway. But let's say it is sloppy enough in there to cause extra noise, even though the Carfax looks pretty good. Oil was changed every 10 to 12k. Not sure with what and that's not often enough, but.. how much life left are we looking at? We only drive 6 to 7K a yr. City, which isn't great for it. We turn off the Eco. Kind of depends what it is I'm sure. If it's chain slap, okay $400 in 40k miles for adjusters.
Thoughts?

Odd Piggy

Well, yeah, the noise could be from the environment it’s recorded in. Can’t compare. We have a GLA & a GLB now and they’re just noisy as hell with the hoods open. 6-7k a year of city isn’t great for mileage but it’s good for years. If the previous owner did that and only changed it at 10-12, not even close to enough — fuel dilution.

Since I’m telling stories — Bought a ‘64 Olds 88 in ‘70 from the coroner’s office (yeah, I’m that old!). How it was maintained by the county is unknown, but it ran even though they had torn up everything taking out the police radio. So I went to the library, took out a service manual, and started to restore. After getting all the parts working, I changed oil and filled with the recommended HD30 of the time. Piston slap and rod knock could be heard at idle and the valve train sounded like a sewing machine. What to do??? Boyfriend of girlfriend’s older sister raced boats. He suggested 20W-50 racing oil… Swapped to that, noise went away and I sold it 64k miles later. So maybe…

40k miles is 6 years away for your city use. You may even want something newer by then. M276s are pretty decent engines when they’re right, so hang in there and good luck.

GLKwanter

Fun fact, you can return motor oil to Amazon. The drop down for reason why is even different than a normal return, and gives the option of 'Did not meet expectations'. I would've never thought that was allowed, but it worked with the 0w40 and it's about to work again with $100 worth of Motul. Yes I have found an infinite free oil change glitch. I'll give the Mobile 1 15w50 a go, pocket $50, and record/report back for the f of it.

You know I'm going to say it again cuz I just can't get it out of my head. What would a strong spring inside that oil filled tensioners do to help stabilize the chain at startup? Would it just get so hot it would lose its tension in a few hundred miles? I'm old enough to remember when taking parts off cars fixed things, today though I think it's the other way around, add one? 😂

John CC

If the problem is the tensioner then what you want is a ratcheting tensioner that limits the movement in the slack direction to one ratchet tooth.

If the video is an accurate reproduction of the sound, I'm not convinced the chain is the problem.

If the chain is the problem, I still don't believe the tensioner is the cure. I'd measure the chain for wear, and make sure all the ramps are in good condition before I changed anything.

GLKwanter

"It is also ideal to check the timing components for wear such as chain stretch and guide. Chain stretch is something I am starting to see on these engines, along with guide rail breakage. Mercedes has a special tool for measuring wear on the timing components but a digital caliper has thus far been sufficient. Specifications can be found within WIS (Mercedes workshop information system) or on many of the applications within AllData or Mitchell repair information databases."

I'd measure it, if I knew sizes. I'd also check tensioners again, if I knew how they function. Every one I've held, new and old, seem stuck. The piston in one of the new tensioners popped out during reinstall. I put it back together. It then depressed all the way. I reinstalled it assuming it would expand with oil pressure. I have a $90 tensioner in one side and a $35 one in the other, but they're still new and no improvement.

I assume they just fill with oil and expand. Is there really a moment where less pressure/tension is desired? Seems not. Ratcheting tension seems smarter. Crappy part. They got a redesign, but still fail. It's a fragile tank design.

John CC

Lots to ponder there. First, both new and no improvement. Doesn't that make you wonder if they were the problem in the first place?

Second, If one cost $90, how good is the $35 one?

Third, if they are like the ones in the attachment, they should expand without oil pressure, as far as I can tell, and it sure looks like they won't easily retract.

GLKwanter

I would say tensioners were definitely bad considering condition of the pins in the cam adjusters that were replaced. The tensioners (which had check valves behind them, so you wouldn't think they were the original tensioners) failed the cam adjusters, again I would assume.
Cam adjusters were definitely a problem in the first place. Idle is much improved at startup the "slap" is All that remains. If that's what it is

There's a lower chain tensioner that would get replaced with the whole timing chain kit.

$90 tensioner from Azautohaus first bank I went into, and a $35 one from eBay second bank. I mentioned it cuz there could be a quality difference, but I bought it because it's just a hunk of metal with a passageway through it and a piston. They seemed identical.

​​​​​Every tensioner I've held new and old I've been able to compress with one hand. I'm nor weakling or hulk. It's hard, but they're also not spring loaded. They compress sort of chunky. They push back but not to the same spot. I've only been able to get that one apart, that sprung apart. But there was no spring inside. I've got two old ones I've been beating one but I can't get the Piston out to look inside. Their total functionality is still a mystery to me.
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Odd Piggy

The explanation seems to indicate that there should be some spring tension when uninstalled, oil pressure is used when the engine is running, and there should be a ratchet mechanism that adjusts it out so the chain doesn’t start completely loose.

Never got into the tensioners on my GLK. It was the most reliable vehicle I had ever owned. The tensioner on the C250 (notorious for other reasons) was completely mechanical with a ratchet to hold it open. So it kind of makes sense that MB would use similar logic on later engines.

John CC

Yeah, if it works like the one in the WIS it has to fully extend before it can compress at all.

Chris1979

I have the m272 engine and on mine from what I've seen on write ups and you tube. When they change the tensioner the way you do it is unplug the fuel pump fuse and crank it so the tensioner opens up and puts pressure

John CC

Here's a real long shot...

If the tensioner works as described in the document, and the tensioner is able to extend to its limit as installed, then it won't ratchet, and every start will be like the first.

Odd Piggy

.

GLKwanter

Ya that's the go to video for many swapping cam adjusters. He likes his vise grips too much 😂
I doubt he solved the rattle at startup, just the labored idle. Like many they never let you hear a cold start after cams get swapped.