1970 250C Knocking.... - Mercedes-Benz Forum

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post #1 of 3 (permalink) Old 03-31-2009, 06:32 PM Thread Starter
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1970 250C Knocking....

Yes, I am new to the Benz and Benzworld, (previously a VW restorer). But I have bought a 250c today and of course when looking at it and test driving it everything was perfect....drove it home, about an hour +/-, and now she knocks at odd RPMs. Not really consistant either, just once in a while I get a rattle out her. Any Ideas? I am really hoping it is not a connecting rod bearing, but that is where I am leaning at the moment. Thanks for your time.
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post #2 of 3 (permalink) Old 04-01-2009, 09:33 AM
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Oil pressure relates to rod knocks, hot idle should be greater than 15psi

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post #3 of 3 (permalink) Old 04-01-2009, 10:32 AM
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First off, is it a rattle or a knock? Is it a knock sound with a deep tone, like a larger part? More of a tap, or somewhere in the middle? The deeper sound could be a rod bearing at the crank. In the middle sometimes is a wrist pin. Since you say it is not constant or at the same rpm and you said "rattle", the valve train could be suspect in my opinion. If you can get it to make the noise in your driveway you can use a mechanics stethascope (SP?), or a long screwdriver with your ear to it to isolate the source (Old mechanics trick, and I would urge extreme caution doing either of these) you will be amazed at what you can diagnose with this method.

Good luck.
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