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  #1  
Old 12-04-2009, 01:47 PM
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Knock or Nailing?

Hello

I am interested in buying a 300SD I think 1984. It is making some noise. Can anybody explain the difference between a knock and injector nailing? Or better yet have a sound bit to show the difference?

I would post a sound bit myself, but I don't have the equipment.

I owned diesels before but just never had one that knocked or nailed.

Thank you in advanced.

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  #2  
Old 12-04-2009, 03:20 PM
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A knock is a lower pitched sound than the Nailing.

The Nailing sound is closer to the detination or pre-ignition sound made by a gas Engine than it is to a knocking sound. It has a lower pitched sound than the detination sound but has about the same duration.
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Old 12-04-2009, 03:38 PM
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I think I got it. But still not so sure. It does however knock or nail heavily when cold.
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Old 12-04-2009, 05:02 PM
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If it's when cold, that could just be nailing. I think rod knock isn't dependent. Is it irregular and sounds a like a ticking sort of?
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Old 12-04-2009, 05:10 PM
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Not sure. I know it sounded like a pretty bad knock or something upon cold start up. Then warm it was I guess quieter, I guess almost a ticking noise, but not as harsh as start up.
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Old 12-04-2009, 05:11 PM
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When your Glow Plug Light goes out keep the Key in that position for and additional 20 seconds or until you here a click under the hood and Start the Engine.

If it nails less you have something going on concerning the burning of the Fuel in the Combustion Chamber.

If you have not done it already I would look at the pictorial on the Diesel Giant site on checking the Glow Plugs. It will take longer to look through the pictoral than the time it takes to check the Glow Plugs.

Also, when the page at the site opens up it appears that there is not much there; you have to scroll down the page to see more.

If the Glow Plugs seem to be OK. Other causes of Nailing are Fuel Injection Pump Timing, Injectors with worn Nozzles and/or low opening pressures, and low Compression (could be due to Valves not being adjusted as well as wear on the Engine).
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Old 12-04-2009, 05:16 PM
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The owner says it has new glow plugs. There is no stumbling on the engine when started cold. It would be nice if this was an easy fix. The car is pretty much in good condition and I think a good price.
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Old 12-04-2009, 05:24 PM
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Rev the engine up,and see if the knock goes away if it does its not too likely that it is mechanical.If the knock continues with the engine revved up push the stop lever under the hood if the knock stops while the engine is still spinning when you push the stop lever
it is caused by something in the fuel system.
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Old 12-04-2009, 11:13 PM
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Quote:
Originally Posted by ludwig View Post
Not sure. I know it sounded like a pretty bad knock or something upon cold start up. Then warm it was I guess quieter, I guess almost a ticking noise, but not as harsh as start up.
I always thought nailing sounded like a rock(s) rolling around inside a metal can.
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Old 12-04-2009, 11:21 PM
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Originally Posted by WhoWhat View Post
I always thought nailing sounded like a rock(s) rolling around inside a metal can.
That's a good description. Or maybe someone sharply hitting metal with a hammer.

A knock is a "heavier" sound.
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  #11  
Old 12-05-2009, 08:42 AM
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Quote:
Originally Posted by ludwig View Post
Not sure. I know it sounded like a pretty bad knock or something upon cold start up. Then warm it was I guess quieter, I guess almost a ticking noise, but not as harsh as start up.
If you have good oil pressure at startup, and it is louder at startup than when warm it is likely fuel system issue. Knocks typically get worse as the oil gets warm and looses viscosity.

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