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'88 560SL '91 420SEL '73 280SEL '59 220S '73 450SL '74 450SL '86 560SL
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Discussion Starter #1
I recently purchased a 560SL (62K) with an engine knock. Thought it was the timing chain. Chain was stretched at 6 degs which is still in spec. Replaced oilers, chain, guides and tensioner. Also replaced plugs, wires, cap and rotor. Ran the engine without starting and was able to reach 3 bar. Started the engine and the knock is still there. Sounds like it is coming from the right rear. It is a loud metallic knocking, not a ticking. I pulled the valve covers and don't see any broken valve springs and all of the hydraulic compensators are tight, i.e. no play. The cam lobes are all very clean and don't show any signs of wear.
I disconnected each plug (1 thru 4) with no change. I was thinking that if it was a connecting rod, then not having that cylinder fire would change the knock.
I'm not sure where to look next.
I have a video or audio file but I can't figure out how to attach it.
 

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1983 380 SL
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2,421 Posts
Knocks are never a good thing. Usually indicate rod or main bearing... possible wrist pin also. However, Mercedes doesn't use bearings on the cam towers, which are made from aluminum.

Here's a photo. Notice the area where the cam rotates inside the tower... no bearing, just aluminum. I'd check the cam towers for wear

MercCamTowerCleaned.jpg .
 

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1983 380 SL
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2,421 Posts
I would not call that sound a knock... it's way more ticky than a knock. Is the engine idling high? That loud tic sounds way too fast to be a valve. A valve only opens once every 4 rotations. If it was a valve it should sound a lot slower.
Did you check the cam towers for wear?
That sound is a lot like the sound I had (not exactly but close) that got me to pull the engine and check the heads. When I pulled the heads I found #6 piston and cylinder walls badly scored.
MercNbr6BeforeHone.jpg MercNbr6Piston.jpg
 

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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500seAMG +250seStkW108 350sl4spdX3 500secEuro
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21,920 Posts
There’s some ugly noise in the first half second of the video that I suggest focusing on. Once the car is running, you can only hear what sounds like a ticking.

I suggest taking the wire off the coil, disconnecting the power to the fuel pump (via the pump wires or the fuel pump relay) and then taking two more videos:
1) with plugs in while you crank the starter
2) with spark plugs removed while you crank the starter.




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1979 450SL UK spec
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1,248 Posts
I agree with Jyuma, sounds like the noise I had from my old engine caused by worn cam bearings.

The bearings and cam shaft were all toast! Caused by a badly fitted oiler tube by a previous owner. It was cheaper to buy a second hand engine than a new set of bearings and cam.

If you remove the followers then see if you can feel any movement in the camshaft.
 

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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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9,732 Posts
If you pull the coil wire make sure you ground it or bad things will happen.
 

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Not quite exhaust leak like ... but maybe worth checking. Engine also sounds very tight / weazy esp when you shut it down.

Whats it sound like without spark and fuel just cold cranking.?


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1986 560SL with M120 V12 Engine, 1988 560SL Stock
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9,732 Posts
Not quite exhaust leak like ... but maybe worth checking. Engine also sounds very tight / weazy esp when you shut it down.

Whats it sound like without spark and fuel just cold cranking.?


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I agree. Doesn't sound exactly like exhaust but the video sound reproduction could be responsible for that.
 

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'88 560SL '91 420SEL '73 280SEL '59 220S '73 450SL '74 450SL '86 560SL
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47 Posts
Discussion Starter #16
Here is the latest. The flex plate is fine. There is no noise during cold crank with plugs in. Any reason to try it with plugs out? The knock is every other rotation. Attached is a trace of the audio. The engine is idling fast 1500 rpm. The trace shows about 13 knocks/sec which is 780 rpm.
Why would a worn cam tower make a knock? Should I just release the followers and rotate the cam?
 

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'88 560SL '91 420SEL '73 280SEL '59 220S '73 450SL '74 450SL '86 560SL
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47 Posts
Discussion Starter #17
Shouldn't an exhaust leak would be 2 per revolution per side. Each piston fires every other rotation and there are 4 pistons.
 

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'88 560SL '91 420SEL '73 280SEL '59 220S '73 450SL '74 450SL '86 560SL
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Discussion Starter #18
The video that I sent was with all belts and the fan removed.
 

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'88 560SL '91 420SEL '73 280SEL '59 220S '73 450SL '74 450SL '86 560SL
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Discussion Starter #19
If you pull the coil wire make sure you ground it or bad things will happen.
What is the correct way to disconnect spark. I always pull the connection from the coil to dizzy.
 

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'80 450SLC Afro RHD Ikonengold
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2,762 Posts
there's a ringing sound to it unless it comes from the recording device

Have you popped the tappet covers?
 
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