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I have a 2012 c250 (64k miles) that's rattling on start up

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and having difficulties cranking. When...
I have a 2012 c250 (64k miles) that's rattling on start up and having difficulties cranking. When cranked the engine makes a subtle tapping noise that sounds like it's coming from the valve train. I pulled the valve cover and checked timing but according to diagrams everything looked OK (could be wrong. I took photos of intake and exhaust sides). The timing chain and cam shaft gears looked to be in good condition visually. All teeth were intact and showed no signs of wear.
The only codes I've been given is a camshaft position sensor-intake but I swapped the intake and exhaust sensors and nothing has coded since.
What's the next check? Can I check the adjusters or should I go ahead and assume it's a stretched timing chain and replace it.
Submitted: 3 months ago.Category: Mercedes
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9/5/2017
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago
Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 5,151
Experience: 15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

Michael may i have your vin?

there have been many different issues we have had in this engine,

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Customer reply replied 3 months ago
WDDGF4HB6CR221795
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

Here is a bulletin we had, its just for info not a fix, we have had tensioner issues, stretched chain issues and gear failure.

can you send me pictures of what you have torn apart so far?

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

ok explain move it in the wrong direction 30 degrees?

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Customer reply replied 3 months ago
When manually turning the engine over at the crankshaft I could turn the crank clockwise roughly 30 degrees before resistance was felt (I used an accessory pulley to turn it with spark plugs taken out. When this resistance was felt the serpentine belt would slip. When turned counter clockwise the engine turned indefinitely. I haven't found any documentation as to if this limited clockwise rotation is OK or not.
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

ok, did you take the belt off and recheck? we have a alternator pulley/clutch that can fail.

it is a one way clutch, the engine should rotate freely any direction however with the cam phasers you never want to rotate counter clockwise you will possibly touch valves.

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Customer reply replied 3 months ago
The belt and pulleys rotated either direction freely. The engine is what did not Rotate. The engine runs fine other than valve/timing noise. According to the photos I supplied does it looks like it could be a advanced/retarded timing issue?
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

I only got one photo, that makes sense now to what you meant, 1183 is the only photo that came across

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

I am interested in the slack of the adjuster and the relation of crank to cam.

here are some documents for you.

some you obviously know how to do already.

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Customer reply replied 3 months ago
Intake side. I notice there's an obvious different in the lines on the camshaft and the lines on the adjusters. All documentation on checking timing I've ran across who two lines on the camshaft. I know have one (and the line on the adjuster). To clarify the line that needs to line up would be the adjuster as shown in the photos (which would be the same lines shown lining up in documentation provided above. Correct?
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

correct it looks like your exhause is slightly retarded and the intake is slightly advanced with seems like a stretched timing chain, i dont think its enough to jump a tooth as you are very close. if you were to line up either camshaft i am not sure you would be a tooth off, were there no check engine light or codes?

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Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

I have to step away for a few, i will check back soon. Lou

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Customer reply replied 3 months ago
Camshaft position sensor. Bank 1. Sensor a. P0340.
This Should be the intake side. I ordered a new sensor since the shipping time would be a roughly a week but afterwards I tested the wiring and both intake and exhaust sensors and both tested OK and showed nearly complete voltage drops when close to metal. I swapped the sensors with the theory of the "intake" sensor was bad on the intake side it would throw a code on the exhaust side after it is swapped. This was two weeks ago with no codes. This code happened right before my crankingnissue appeared. Sometimes my car will crank on the first try ( and sounds rough. Valve noise or metallic clicking. After a few seconds the sound goes away or is dampened until the car is cranked again. I'm assuming this is due to oil reaching the head). Sometimes though it will take three tries to crank the engine. Like it is looking for a position signal or the timing is off...I apologize if this is a lot of information at once. I've been researching the issue since I got the car because I knew it would happen eventually. Short of replacing everything that touches the timing chain I haven't found documentation outlining the root cause for this engines issues...
Mercedes Mechanic: Lou P. master tech, Mercedes Technician replied 3 months ago

ok, i am curious of the slop in the timing chain , the tensioner should hold slight pressure on the chain, what I would do is remove the tensioner so it ratchets out all the way and reinsert it to get tension on the chain and set the crank to tdc and see where the timing marks are then at.

then i would change the tensioner if all is ok and if it happens again then you could be looking at a oil pump.

but we also need to see if when the crank is tdc if the intake aligns , it should if it doesnt then it may have jumped a tooth . same with the exhaust. or the crank could have been the one that jumped. like i said there have been too many issues with these to all be the same issue or resolve.

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