Hydraulic'd engine - bent valve or bent conn rod?

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Alex_M

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Hey all! Hopefully one of you can chime in and confirm or deny my diagnosis.

2002 6.0. Just installed a ton of new parts - heads, cam, lifters.... Injectors.... Allegedly "genuine" AC Delco Made in Germany. Well upon closer inspection after the fact, they shipped from China. Fake Delco injectors.

Anyway - got the engine back together and running. Was smoking some so I shut it down. When I started it again it started to crank, kicked, and stopped dead. One injector had leaked down and filled the cylinder with fuel. Pulled plugs, cranked over fine, cleared out fuel. I reinstalled the original injectors (so much for being proactive) and restarted the motor. I now have a ticking.

I am familiar with both bottom end and top end noise. This one is odd, somewhere in-between, but seems fast for a top end noise. So here I go, crossing my fingers for a bent pushrod. Pulled valve covers and no such luck - all good. Started with valve covers off, nothing obvious. Noise is no louder.

Here's the kicker. I did a compression test on all 8. 7 of 8 showed 175-180 PSI. Cylinder 3 which was full of fuel showed 150#. All 8 were leaking off at roughly the same speed, nothing wildly out of line.

So, here's where my logic goes. If it were a bent valve, it would either leak down much faster or it would show zero compression. Since cylinder 3 leaks down at the same speed but shows lower compression, that rod is most likely bent.

By the end I will at a minimum pull the head and check the valve as well as measure piston to deck height to confirm diagnosis, but in the mean time I'd love input on this, possible alternatives. Thanks guys
 

OR VietVet

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You said, "When I started it again it started to crank, kicked, and stopped dead". That statement, if you said it correctly, says you did not start the engine, it says it stopped dead while cranking the engine. If that is correct, then I suspect that you have a damaged flex plate. Happens when you have a cylinder full of fluid, try to crank engine, offending piston gets close to TDC, the fluid does not allow any further movement and kicks back at the starter drive and then the damage gets to the flex plate and causes a crack. I have seen the nose of the starter break off completely as well, so if I was you, I would remove starter to inspect for breakage or cracks and inspect the flex plate thoroughly.

By the way, change the oil and filter too.
 
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Alex_M

Alex_M

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Ah! Didn't even think about flex plate. I will certainly inspect that. And yes, the engine did not actually start. Felt like it tried to light off before it was stopped, but... Obviously didn't.

However, do you have a theory for why the compression would be showing so much lower on the cylinder that hydraulic'd?

I do not think it's because the cylinder was washed down with fuel, because I drove the truck 3 or 4 miles doing testing earlier in the day before the compression test.
 

B-train

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Since it was spinning and abruptly stopped due to hydro-locking, you most likely have a bent connecting rod. It doesn’t take much for it to happen with the rotarirng mass ans the high torque of the starrer. Your compression is lower on that cylinder because the piston isn't traveling as high in the cylinder due to the shortened travel of a bent rod.
 
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Alex_M

Alex_M

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All right, that's what I was afraid of. I'll definitely check the flex plate as you mentioned. Looks like I'll have a good core to build a stroker motor....

Thanks for the input gentlemen.
 

OR VietVet

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All right, that's what I was afraid of. I'll definitely check the flex plate as you mentioned. Looks like I'll have a good core to build a stroker motor....

Thanks for the input gentlemen.
If I might interject here about a stroker motor. Unless you have a specific reason for a stroker, I would recommend a less expensive way to wake up a stock engine. Do a tune with Black Bear Performance. They are a vendor here and are listed on the Home/Forums page. You can customize the tune or do a "traditional tune" like I did. The engine acts normal till you ask more of it. Then it wakes up and turns in to fun. That tune, matched up with my Hellwig Performance front and rear sway bar kits, adds up to loads of fun and performance.
Like I said, mine is the traditional tune but you have other choices to go with. It does not cost anything to contact them and talk about possibilities.
 
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Alex_M

Alex_M

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Oh, I tune all my vehicles. Bought HPTuners years ago. The 6.0 will just get replaced with a reman 6.0 for now to get back on the road quick, but I'll keep the old motor for a core for a future project.

Thanks!
 

Mudsport96

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Eh, hit the junkyard and grab one rod and piston combo and throw her back together. Did that with a 4.8 years ago because a guy i know drove through deep water and did basically the same thing. Truck ran for another 50k miles before he traded it in for a 2500 hd.
 
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Alex_M

Alex_M

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Already would have for any of our other vehicles, but this one I need to be back to 100% ASAP, and not have any doubt in it. This is my work truck that I rely on every day, only one in the fleet that gets "the royal treatment".
 

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