2008 6.7 Cummins Engine Knock

In my opinion firing the motor again without first determining the souce of the noise is foolishness. An oil sample will tell what wear metals are present. A bore scope in the injector holes will reveal valve/piston issues. Inspecting the flex plate through the starter and inspection holes should give one a good idea of whether there is a problem back there.
 
LReiff said:
In my opinion firing the motor again without first determining the souce of the noise is foolishness. An oil sample will tell what wear metals are present. A bore scope in the injector holes will reveal valve/piston issues. Inspecting the flex plate through the starter and inspection holes should give one a good idea of whether there is a problem back there.
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^ this
 
I had the crank bolts loose on my puller. At idle it sounded terrible, rev it to about 2000 and the sound went away. Have also seen the bellhousing adapter bolts come loose and cause a sound that sounded terrible.
 
Ive seen a piece of piston crown break off and get mashed between good crown and the head that was a tough one. No other symptoms except the racket.
 
Lots of opinions on this one for sure. I'm going to take a close look at it this weekend and see if I can help them troubleshoot it.
 
Another vote for flexplate or something in that area.

Had a 12v that ripped the lugs off the convertor, talk about a nasty sound!!
 
Im still going with valve seat. The one i did sounded EXACTLY the same. Like Rieff said, look everywhere you can without starting it again.
 
I think its the #6 rod bearing cause I built to motors last year because of the same sound. The trucks were low on oil and the #6 rod id the last one to get oiled.
 
My ford with 351 broke the flex plate and it had a very similiar sound like that can you be more specific on where the sound comes from? Bellhousing, bottom end, or top end?
 
My vote is going with the valve train. Not sure what exactly on the valve train but it's gonna be there IMO. It sounds like it's coming from the top half of the engine. But who really can say what it is til it's been torn apart and checked? I know I can't.
 
Has this engine been torn down yet,,.I have the same problem and trying to figure it out,
would like to hear what you found. When I say the same problem I mean I could have made that video, I have exactly the same sound.
 
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I'm scheduled to go help diagnose the problem tomorrow night. The mechanic is backing away from it so I can do a little "shade tree" diagnosis.

I've never worked on anything newer than a 2001, so this is new to me.


I did speak to the mechanic for a good 30 minutes and he swears up and down that with his stethoscope, the sound is definitely coming from #1 or #2 cylinder and that the frequency is perfectly matching one of the valves. He also said he checked the flex plate and it's not the problem.

I've got an hour tomorrow to figure out the problem what should I check?
 
i would feel the valve bridges as its running if you start it although i dont advise this. it sounds like a seat and the only good way is with the head off
 
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