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  #1  
Old 12-10-2018, 12:04 PM
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Join Date: May 2017
Posts: 28
1960 190B (gas) engine knock

Hi everyone
My engine has a funny noise at low idle. Sort of a knock that isn't consistent. As the engine warms up it gets worse. I thought it was a leaky manifold gasket so I replaced it. Knock still there. I thought it might be the water pump. I took the belt off for a couple of minutes, knock still there.

Now I think its the timing chain and the timing chain tentioner.
Took the valve cover off. I lined up the compensating washer notch to the camshaft notch to get cylinder 1 lined up. Then I looked at the pointer on the crank shaft. It looked like about 5 degrees off.

I took the tentioner out to inspect and clean it. When I took the tentioner out it wouldn't move as if it was stuck. I took it apart everything came out easily.
I cleaned it pretty thoroughly including the little oil holes. It now moved freely on the spring. I reinstalled it in the head bleeding it with oil in the reserve.
I did notice some rough wear back where the 27 MM cap screws on. Other than that it looked ok

Started the engine. Knock was still there. Hmmmm.
Not as bad as before.
Could it be I have a stretched timing chain?
Should I replace the tentioner?
Thanks
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  #2  
Old 12-11-2018, 12:05 PM
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Join Date: Oct 2012
Posts: 10,665
One way to track a noise down is with a stethoscope. There are automotive one sold. They look and work like a heart stethoscope but they have a long metal bar coming out of them.

Just start the engine, put the plugs in your ears and start probing. This will at least narrow down the area to look at.

If you want to go cheap you can use a thin dowel rod to do the same thing. Just put one end on the engine and the other in your ear. The bad part about this is if you move the rod to a moving part of the engine (also known as anywhere up front) you could get the rod punched through your brain. So this is not recommended.

I have seen old time mechanics use a pry bar to do the dowel rod trick. Same results; same dangers.

Stethoscopes are cheap, and if all you can find is a heart one then use the dowel rod as a probe. This is dangerous. Know that going into this. But it quickly narrow down the part of the engine to work on.
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Old 12-11-2018, 05:47 PM
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Posts: 28
Thanks Mr Billy Idle-
Harbor Freight had one for $3.88 - I bought it and I think I hear the noise coming from the chain guides. I'm going to get the guides out and check them , they're only plastic. The Mercedes classic center wants a lot of money for them so I have to be sure.
Stethoscope was a great idea, the rod punched through the brain danger is over rated. You simply pull the rod out and get on with things
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  #4  
Old 12-11-2018, 06:51 PM
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Join Date: Dec 2010
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If the noise starts after the engine warms it could be a rod bearing. Start your engine and let it warm up. Once it's warmed a bit pull each plug wire off one at a time and see if the knocking sound goes away. If it pretty much disappears you can expect a mechanical problem.
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  #5  
Old 12-11-2018, 09:45 PM
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Location: Long Island, NY
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Did you check your valve clearances recently? -CTH
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  #6  
Old 12-12-2018, 09:12 PM
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Hi CTH and BENZ Dr-
Thanks for the messages.
CTH , yes I did adjust the valves. They were a little out but very good.
Benz Dr-
Boy you got me scared. I did exactly as you said, I unplugged individually each spark plug and listened for the noise. It was still there. I'm so relieved, rod knock is a big deal.
So I listened again for the noise with the stethoscope. The noise is most pronounced at the front of the engine,down low, where the lower driver side timing chain guide is.

I took the cylinder #1 spark plug out. I used a piece of thin rod to find top dead center.
I noted the distributer was at cylinder #1.
Then I looked down at the marking on the balancer wheel/pulley. it's showing approx. 11 degrees off.
I believe either the balancer is off ( I heard the dowels can wear out in their holes) or the chain is stretched and flapping against the worn out guide.
So tonight I'm busy taking out the radiator and water pump to get at the guide dowels.
I'm going to get it apart and report back on what I find.
Any comments are very much appreciated. Thanks
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  #7  
Old 12-12-2018, 09:34 PM
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Posts: 679
The balancer may be the noise, rock, pull on it to see if it moves.

Good luck!!!
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Does a Caddy stretch? No, but a Mercedes bendz.
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