Guess the source of my Knock

[Vanzal15]

The SOUND:

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Hints:
1. Started while leaving work and got progressively louder on my 30 minute 12 mile commute home.
2. Shakes the cab a bit.
3. Filled both tanks with diesel 5 miles before work.
4. 200k miles on motor.

Post up your guesses. I'll probably start the investigation next weekend.

 

[79jasper]

Rod, knock knock knocking on heavens door.

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[jwalterus]

I'm going to guess from your description of events that your "diesel" you topped off with was a little high in Ethanol content, maybe about 10%?
In other words, give your fuel a sniff test because I think you got RUG instead.........

 

[tjsea]

I second possible gasoline instead of diesel. Would make sense since you just filled it up. Otherwise I'd start looking to valve issues. It almost sounds like its coming through the intake.

 

[IDIBRONCO]

It almost sounds like its coming through the intake.

That's my guess too. You almost never hear of a spun bearing on one of these engines without extreme circumstances. It seems to be almost common on the GM 6.2/6.5 engines.

 

[Joseph Davis]

Wow now that is a loud knock, dead cylinder with valve hitting piston? you still have screen on throttle body? lol, Well sorry for the bad luck. I hope it is something simple.

 

[Ethan Smith]

**** that sounds like me hitting my head into the wall when the wifes ******** at me

 

[Garbage_Mechan]

You guys are silly. That ain’t a knock. It’s a valve issue. Popping back into the intake.

 

[Garbage_Mechan]

Either something is keeping the intake valve from sealing ( bent, sticking, bad guide, weak or broken spring) or the exhaust isn’t getting out because of an exhaust valve issue (broken rocker, bent pushrods, lifter or cam issue)
When the exhaust valve isn’t opening the trapped air comes back out the intake when it opens. I would guess the intake.

 

[Macrobb]

Pull valve cover, look for loose rocker or bent pushrod. Mind you, a pushrod would have to be very bent to cause thumping like this; it's not a "this pushrod isn't flat within .005"" type issue - it'd be blatently obvious.

 

[Vanzal15]

Yall, thanks for the ideas. I decided to take a moon shot and fill the fuel filter with fresh diesel form a "trusted" gas station. I fired the old girl up and let her idle for 1 minute. no improvement. The GF is whining i don't spend enough time with her so I promised i would take her floating on Saturday. Right now i got Sunday in my crosshairs to take the valve covers of and see what i can find. Pix to follow.

 

[Vanzal15]

Found it.....

Rod is not bent. Rocker is not bent. Spring does not appear to be broken.... If I angle the rod into it's hole it catches on a higher and lower surface. Is it possible it is slipping off the lobe on the cam?

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[79jasper]

The push rod doesnt engage the cam directly.
Sounds like a collapsed lifter.

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[Vanzal15]

What do you know about the surface/connection between the lifter and rod 79? Both the "good side" and bad side of that piston's valves have angles at which I can insert the rod that it goes in much deeper. Not sure if there is a small pocket on the lifter that the rod fits inside and if you miss the pocket the rods slips deeper or what.... Hope that makes sense. I'd imagine its impossible to remove the lifters from the top of the block after the head is removed? If it's rebuild time I'd likely take a few months to rebuild and upgrade this thing. If I can patch it for a few months though that would be ideal as I'm doing a bunch of landscaping and house work that I was counting on using the truck for.


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[79jasper]

Maybe this pic will help. No need to remove the head.

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