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What does knock sound like?

What does knock sound like?

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raklet
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I started starting the 70D a while back. It ran for a few minutes and then died. I double checked everything and found it was almost out of oil. I put in about 6 gallons worth and turned it over again. It runs without shutting down and (to me) the engine sounds really good.

Supposedly, this engine has a knock in it, but I don't hear anything that sounds like a knock. What does knock sound like? What should I be looking for?
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Sun, Apr 5, 2009 2:25 AM
SJ
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There are two things right off hand to check and with it idling take a 3/4" open end wrench and open each fuel line one at a time till fuel comes out and see if one of them takes the knock away when it,s open and if it goes away sounds like a bad nozzle. You could swap that nozzle with another one in the engine and see if the knock follows and if so pretty much pins it down to a bad nozzle. If the knock is still there take the oil filters out and see if they have some aluminum grindings or chips caught in them and if so sounds like you got trouble there, scored bearing or bearings.
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Sun, Apr 5, 2009 3:48 AM
raklet
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Reply to SJ:
There are two things right off hand to check and with it idling take a 3/4" open end wrench and open each fuel line one at a time till fuel comes out and see if one of them takes the knock away when it,s open and if it goes away sounds like a bad nozzle. You could swap that nozzle with another one in the engine and see if the knock follows and if so pretty much pins it down to a bad nozzle. If the knock is still there take the oil filters out and see if they have some aluminum grindings or chips caught in them and if so sounds like you got trouble there, scored bearing or bearings.
Sorry, I didn't explain myself well. I am asking what knock sounds like. I don't hear anything. The engine sounds normal to me - just like the other motor grader I have that runs fine. I was only told that the engine has knock when I bought it, but I don't know that for myself.
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Sun, Apr 5, 2009 6:33 AM
OzDozer
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Reply to raklet:
Sorry, I didn't explain myself well. I am asking what knock sounds like. I don't hear anything. The engine sounds normal to me - just like the other motor grader I have that runs fine. I was only told that the engine has knock when I bought it, but I don't know that for myself.
There are many faint knocks and clatters from a engine that's running, and the noise is worse when they are cold. "Diesel knock" is the explosive combustion of diesel fuel under high compression that is readily identifiable with any diesel.

However, audible knocks can be caused by excessive clearances or faulty fuel injection. Clearances larger than normal in (mostly) big end bearings will come across, as a louder-than-normal regular deep knock. The knock is audible above the regular "diesel knock" and generally increases at higher speed, and when the engine RPM is varied slightly but rapidly (the vroom-vroom of rapid throttle increase and decrease).

Another source of knock is excessive wrist pin clearance. This is generally louder but lighter in pitch than a big end bearing, and is regular through the rev range and throttle application. A mechanics stethoscope is an ideal tool to try and pinpoint knocks.
Have someone operate the throttle, varying the RPM, while you place the stethoscope on the lower parts and upper parts of the engine block, to try and pinpoint the sound source area. Check at idle, and check at higher RPM.

Injection knock is a very loud knock that is alarming, and easily heard. It is caused when air gets into the fuel, or the injectors are faulty, and not atomising the fuel properly. Injection knock can be found easily by utilising the process described above by SJ.
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Sun, Apr 5, 2009 6:58 AM
Oil Slick
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Reply to OzDozer:
There are many faint knocks and clatters from a engine that's running, and the noise is worse when they are cold. "Diesel knock" is the explosive combustion of diesel fuel under high compression that is readily identifiable with any diesel.

However, audible knocks can be caused by excessive clearances or faulty fuel injection. Clearances larger than normal in (mostly) big end bearings will come across, as a louder-than-normal regular deep knock. The knock is audible above the regular "diesel knock" and generally increases at higher speed, and when the engine RPM is varied slightly but rapidly (the vroom-vroom of rapid throttle increase and decrease).

Another source of knock is excessive wrist pin clearance. This is generally louder but lighter in pitch than a big end bearing, and is regular through the rev range and throttle application. A mechanics stethoscope is an ideal tool to try and pinpoint knocks.
Have someone operate the throttle, varying the RPM, while you place the stethoscope on the lower parts and upper parts of the engine block, to try and pinpoint the sound source area. Check at idle, and check at higher RPM.

Injection knock is a very loud knock that is alarming, and easily heard. It is caused when air gets into the fuel, or the injectors are faulty, and not atomising the fuel properly. Injection knock can be found easily by utilising the process described above by SJ.
Raklet, click on the links below. I got piston and rod knocking video's. Then a picture of whats next 😮


#6 Piston Knock,
http://www.youtube.com/watch?v=c2_k4QvQmPw
http://www.youtube.com/watch?v=Hg7MiHwFDIw

#2 Rod Knock,
http://www.youtube.com/watch?v=9ks9T6cPxxI
http://www.youtube.com/watch?v=GVNLx0UsVzE

I think the camera is shaking because I'm crying LoL
Attachment
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Sun, Apr 5, 2009 7:19 AM
cr
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Reply to Oil Slick:
Raklet, click on the links below. I got piston and rod knocking video's. Then a picture of whats next 😮


#6 Piston Knock,
http://www.youtube.com/watch?v=c2_k4QvQmPw
http://www.youtube.com/watch?v=Hg7MiHwFDIw

#2 Rod Knock,
http://www.youtube.com/watch?v=9ks9T6cPxxI
http://www.youtube.com/watch?v=GVNLx0UsVzE

I think the camera is shaking because I'm crying LoL
Attachment
I thought that I was going to have to make a post like this this yesterday.

I went out to the ranch for the first time in a long while after working on a hard deadline on a big history changing R&D project at work for the last few weeks.

When I fired up my old D4 6u I noticed a hollow sounding knock. Shut it down, luckily there was a Cat mechanic working on one of my relatives challengers. Asked how long the cat was sitting in the back of the barn, told him a few months, he grabbed a 3/4" wrench started it up and started bleeding injectors and after #4 was bleed it went away, and I was out making washboards.


I guess I was lucky on my tractor but with little or no oil in the motor grader I would be cutting into filters and "looking for gold" as some mechanics would say.
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Sun, Apr 5, 2009 8:19 AM
raklet
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Reply to Oil Slick:
Raklet, click on the links below. I got piston and rod knocking video's. Then a picture of whats next 😮


#6 Piston Knock,
http://www.youtube.com/watch?v=c2_k4QvQmPw
http://www.youtube.com/watch?v=Hg7MiHwFDIw

#2 Rod Knock,
http://www.youtube.com/watch?v=9ks9T6cPxxI
http://www.youtube.com/watch?v=GVNLx0UsVzE

I think the camera is shaking because I'm crying LoL
Attachment
[quote="Mike Mc"]Raklet, click on the links below. I got piston and rod knocking video's. Then a picture of whats next 😮

[/quote]


😮 That rod knock video is terrible! I don't have anything that sounds like that.
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Sun, Apr 5, 2009 9:39 AM
Aaron
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Reply to raklet:
[quote="Mike Mc"]Raklet, click on the links below. I got piston and rod knocking video's. Then a picture of whats next 😮

[/quote]


😮 That rod knock video is terrible! I don't have anything that sounds like that.
Mike, got a little over rev going on there to cause that or or pulling too hard with the 8 on.
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Sun, Apr 5, 2009 10:39 AM
Oil Slick
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Reply to Aaron:
Mike, got a little over rev going on there to cause that or or pulling too hard with the 8 on.
A- I bought the truck with a tired motor (#6) and gave it a complete in frame rebuild. About 200 miles after the rebuild it spun #2 rod bearing. Called the engine rebuilder and they sent a tow truck and put a brand new crank in for free. The suspected cause was an obstruction in the oil passage. Not my driving 😎
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Mon, Apr 6, 2009 3:14 AM
raklet
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Reply to OzDozer:
There are many faint knocks and clatters from a engine that's running, and the noise is worse when they are cold. "Diesel knock" is the explosive combustion of diesel fuel under high compression that is readily identifiable with any diesel.

However, audible knocks can be caused by excessive clearances or faulty fuel injection. Clearances larger than normal in (mostly) big end bearings will come across, as a louder-than-normal regular deep knock. The knock is audible above the regular "diesel knock" and generally increases at higher speed, and when the engine RPM is varied slightly but rapidly (the vroom-vroom of rapid throttle increase and decrease).

Another source of knock is excessive wrist pin clearance. This is generally louder but lighter in pitch than a big end bearing, and is regular through the rev range and throttle application. A mechanics stethoscope is an ideal tool to try and pinpoint knocks.
Have someone operate the throttle, varying the RPM, while you place the stethoscope on the lower parts and upper parts of the engine block, to try and pinpoint the sound source area. Check at idle, and check at higher RPM.

Injection knock is a very loud knock that is alarming, and easily heard. It is caused when air gets into the fuel, or the injectors are faulty, and not atomising the fuel properly. Injection knock can be found easily by utilising the process described above by SJ.
Ok, opinion time.

I found a local old gent that has 40+ plus years working on CATS. He came out and listened to the engine with me. He couldn't hear anything right off and had it run for several minutes to get good and warm, still with nothing apparent showing up. He told me to get the tires fixed so I could take it out and put a load on it.

We were about to shut it down when he messed with the throttle linkage. Finally, we could hear some noise. It occurs when the throttle is rapidly moved from high rpms to low rpms. The noise is not audible going from low rpms to high rpms. We cracked each of the fuel lines, but no change there. The noise can still be heard, but not at any steady rpm level. Only when the engine is retarded from high rpm to low.

The old gent suggested I remove the inspection covers and check to make sure the rods are tight and inspect the bearings. I guess that will be my next step. Also I am going to change the oil filters and look for metal shavings. Any other opinions, suggestions?

Thanks
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Tue, Apr 7, 2009 2:44 AM
Old Magnet
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Reply to raklet:
Ok, opinion time.

I found a local old gent that has 40+ plus years working on CATS. He came out and listened to the engine with me. He couldn't hear anything right off and had it run for several minutes to get good and warm, still with nothing apparent showing up. He told me to get the tires fixed so I could take it out and put a load on it.

We were about to shut it down when he messed with the throttle linkage. Finally, we could hear some noise. It occurs when the throttle is rapidly moved from high rpms to low rpms. The noise is not audible going from low rpms to high rpms. We cracked each of the fuel lines, but no change there. The noise can still be heard, but not at any steady rpm level. Only when the engine is retarded from high rpm to low.

The old gent suggested I remove the inspection covers and check to make sure the rods are tight and inspect the bearings. I guess that will be my next step. Also I am going to change the oil filters and look for metal shavings. Any other opinions, suggestions?

Thanks
I have found that a rod or main bearing knock is usually louder under load. It's the piston pin that will knock when engine is unloaded from high rpm to low.
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Tue, Apr 7, 2009 3:54 AM
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