Basic Diesel Question
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Junior User
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From: Harvest, AL
Basic Diesel Question
What causes a diesel engine to "rattle"? I have a 6.0 and am experiencing the loud-to-quiet-to-loud that many others are experiencing. 
Even when the engine goes silent, it's still running. Anyway, just curious about the cause of the diesel rattle.
Even when the engine goes silent, it's still running. Anyway, just curious about the cause of the diesel rattle.
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From: stoneboro, pa
raddle/tickety-tick sound in our HEUI diesels is mostly from the activation of the injectors.
the diesel clacking sound is actually the piston rocking in the bore and "falling" from one side of the cyl to the other as the rod center moves from BTDC to TDC and down ATDC. the fire in the hole is pushing on the top of the piston and it wants to move away from the pressure so it hits the pressure side of the cylinder.....
i know it sounds complicated, but its really not....just visualize the inner workings of the motor
the diesel clacking sound is actually the piston rocking in the bore and "falling" from one side of the cyl to the other as the rod center moves from BTDC to TDC and down ATDC. the fire in the hole is pushing on the top of the piston and it wants to move away from the pressure so it hits the pressure side of the cylinder.....
i know it sounds complicated, but its really not....just visualize the inner workings of the motor
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Joined: Mar 2004
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From: Hendersonville, NC
Originally Posted by bighoss550
raddle/tickety-tick sound in our HEUI diesels is mostly from the activation of the injectors.
the diesel clacking sound is actually the piston rocking in the bore and "falling" from one side of the cyl to the other as the rod center moves from BTDC to TDC and down ATDC. the fire in the hole is pushing on the top of the piston and it wants to move away from the pressure so it hits the pressure side of the cylinder.....
i know it sounds complicated, but its really not....just visualize the inner workings of the motor
the diesel clacking sound is actually the piston rocking in the bore and "falling" from one side of the cyl to the other as the rod center moves from BTDC to TDC and down ATDC. the fire in the hole is pushing on the top of the piston and it wants to move away from the pressure so it hits the pressure side of the cylinder.....
i know it sounds complicated, but its really not....just visualize the inner workings of the motor
The more clicking, rattling, vibrating, whistling, and growling noises my truck makes the better, as far as I am concerned...Just lets the people around me know the beast is alive
Post Fiend
Joined: Apr 2004
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From: Great State of Texas
The more clicking, rattling, vibrating, whistling, and growling noises my truck makes the better, as far as I am concerned...Just lets the people around me know the beast is alive
Yeah... and for PSD that means all the moving parts are still moving...not welded togther or disintegrated...No wonder the more noise the better.
Yeah... and for PSD that means all the moving parts are still moving...not welded togther or disintegrated...No wonder the more noise the better.
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Joined: Jul 2003
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From: Stockbridge
Originally Posted by bighoss550
raddle/tickety-tick sound in our HEUI diesels is mostly from the activation of the injectors.
the diesel clacking sound is actually the piston rocking in the bore and "falling" from one side of the cyl to the other as the rod center moves from BTDC to TDC and down ATDC. the fire in the hole is pushing on the top of the piston and it wants to move away from the pressure so it hits the pressure side of the cylinder.....
i know it sounds complicated, but its really not....just visualize the inner workings of the motor
the diesel clacking sound is actually the piston rocking in the bore and "falling" from one side of the cyl to the other as the rod center moves from BTDC to TDC and down ATDC. the fire in the hole is pushing on the top of the piston and it wants to move away from the pressure so it hits the pressure side of the cylinder.....
i know it sounds complicated, but its really not....just visualize the inner workings of the motor
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From: stoneboro, pa
Originally Posted by psdwanabe
I'm far from an expert but, I would think if the diesel knock was caused by the piston doing what you describe, diesels wouldn't last as long as they do. Its my understanding that what your hearing is the actual pressure wave of the ignition process. Thats why a diesel is quieter with pilot injection, the pressure wave is less violent.
its not hitting hard, BTW. its only a few thousanths clearance once warm.
ever herad a real race engine with forged pistons start up cold?(with mufflers) that is the same clacking sound u hear in a diesel.
there may be some sound from something else....... if the flame front is what makes the sound, why doesnt a gasser make the noise? its flame front is much faster and violent than our oil burners????
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From: Harvest, AL
Thanks for the posts. But I'm still a little confused. The 6.0 runs an 18:1 compression ratio. I would think the engine would have to be tight to handle that kind of compression. Even if the clearance is only a few thousands of an inch, would that allow blow-by and loss of compression?
So, bighoss550, when my engine runs totally quiet, what is happening? I can unplug the EGR (see the thread on the EGR & Throttle Plate) and the fluctuation in the diesel sound stops.
As soon as I plug it back up, the change begins again. 
Is the compression ratio dropping? Is the timing changing?
The 6.0 runs an 18:1 compression ratio. I would think the engine would have to be tight to handle that kind of compression. Even if the clearance is only a few thousands of an inch, would that allow blow-by and loss of compression?So, bighoss550, when my engine runs totally quiet, what is happening? I can unplug the EGR (see the thread on the EGR & Throttle Plate) and the fluctuation in the diesel sound stops.
As soon as I plug it back up, the change begins again. Is the compression ratio dropping? Is the timing changing?
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From: stoneboro, pa
Originally Posted by jarmbrester
Thanks for the posts. But I'm still a little confused. The 6.0 runs an 18:1 compression ratio. I would think the engine would have to be tight to handle that kind of compression. Even if the clearance is only a few thousands of an inch, would that allow blow-by and loss of compression?
So, bighoss550, when my engine runs totally quiet, what is happening? I can unplug the EGR (see the thread on the EGR & Throttle Plate) and the fluctuation in the diesel sound stops. As soon as I plug it back up, the change begins again. Is the compression ratio dropping? Is the timing changing?
The 6.0 runs an 18:1 compression ratio. I would think the engine would have to be tight to handle that kind of compression. Even if the clearance is only a few thousands of an inch, would that allow blow-by and loss of compression?So, bighoss550, when my engine runs totally quiet, what is happening? I can unplug the EGR (see the thread on the EGR & Throttle Plate) and the fluctuation in the diesel sound stops.
As soon as I plug it back up, the change begins again. Is the compression ratio dropping? Is the timing changing?it is a tight fit when the piston temp gets high. alum expands more than steel or iron. if it was a tight fit, it would become a "press" fit once hot!!!!!
thats no good
Last edited by bighoss550; Aug 31, 2004 at 08:49 AM.
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From: Harvest, AL
Haven't noticed the smoke. I'll watch for it. "sneeker", in this thread https://www.ford-trucks.com/forums/s...d.php?t=276702, attributes the problem to the exhaust pressure sensor. I'm going to talk to the diesel tech at my dealership about this.
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From: Oshawa/Ontario/Canada
Originally Posted by jarmbrester
Thanks for the posts. But I'm still a little confused. The 6.0 runs an 18:1 compression ratio. I would think the engine would have to be tight to handle that kind of compression. Even if the clearance is only a few thousands of an inch, would that allow blow-by and loss of compression?
The 6.0 runs an 18:1 compression ratio. I would think the engine would have to be tight to handle that kind of compression. Even if the clearance is only a few thousands of an inch, would that allow blow-by and loss of compression?But seriously, I understood the diesel knock was partially due to the running gear (injectors mainly) and partially the pressure wave ... which according to some things I've read is violent enough to cause the cylinder walls to flex (which is the reason for the cavitation ... and the associated processes to prevent it).
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From: Harvest, AL
Originally Posted by ZBeeble
Well... he's talking about the skirt of the piston moving a few thousands of an inch and striking the cyninder wall. It's the "rings" that prevent blow by and maintain the compression.
Anyway, guess that's why these PSD are so tough!
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From: stoneboro, pa
ok, let me be a bit more specific....
at cold or at idle the clack is the skirts.
at hard throttle and high heat the only clatter will be the tink of the fire in the hole. which u will rarely hear.
at cold or at idle the clack is the skirts.
at hard throttle and high heat the only clatter will be the tink of the fire in the hole. which u will rarely hear.