Weird Engine Knock - Valve contact?

D

deerefanatic

Always learnin...
Joined
Aug 27, 2011
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OK guys. Had a guy drag in a 2002 24v with a fairly noticeable tapping noise. All through the rpm range. If you goose it and let off, it taps as the engine coasts down. It also taps a few times as the engine stops when you key off. It's a 6 speed so no flexplate issues.

Says the noise just started all at once while hauling a gooseneck full of hay. Truck has 150k miles, motor was replaced at 50k due to a cracked 53 block. No chips or programmer.

The motor is spewing raw diesel out of the number 6 exhaust port. It runs really rough when you start it and smokes fairly heavy, even when started in my 68 degree shop. I figured broken ring and low compression.

I pulled the head. Number 6 piston and the head over #6 are soaked in fuel. The cylinder walls look great on 6, still have crosshatch, just like the others. Headgasket is good, not blown. BUT, there are 4 noticeable round marks made on the piston where the valves are, like they've been hitting the piston. BUT, neither the piston or the valves are shiny anywhere, like they've been contacting.

What do you guys think? Any suggestions?

Thanks!
 
Man, you did alot of work you may not need to. I would have the injectors checked. My guess is with Weston, cracked nozzle or hung open.
 
Now that's piston contact...

255kms6.jpg
 
That picture right there is basically what it looks like.... Only all black and wet. But you can clearly see the 4 spots where valve contact has occured. All the springs look good and the retainers/keepers are in position. Also, the seats are not dropped as the valves are recessed into the head the same as all the others.

No, injectors have not been checked yet. They are going out Monday morning to be checked.

I still need to figure out though, why the piston on #6 is recessed a good amount in the cylinder when #1 actually protrudes some.
 
if the rod was bent theres no way the piston could reach the valves, it sounds like bad bearings, can you measure the piston movement-play with a dial gauge and turning the crank?
 
Had a guy bring me an 06 this time last year with the #6 piston looking the same way and an intermediate knock. Thought it was a wrist pin, then when we pulled the oil pan and one rod bolt, half the rod cap came with the bolt. If the valve area of the piston is dark and the rest is more light colored like the pic above, that is the piston hitting the head, not the valves hitting the piston.
 
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