2001 Chevrolet Tahoe 5.3 Engine knock - help to identify

[kjetilaf]

Hi

i have an 01 Tahoe 5.3 that got a heavy knocking sound after sitting for approx 14 days.
What happened is a failed start attempt at first, it turned over and instead of starting it just made some noise and did not start,
restarted it and then there was a new knocking sound.
I suspected lifter that needed to be filled with oil, but the sound did not go away after idleing and reving it a little.

What i have done
I have dismantled the top covers on each side, and inspected valvesprings, rocker arms. I cant find anything out of the ordinary here..

I would really appreciate someone with the same type of knock ''frequency'', that have found root cause.
I suspect lifter or bent rod, but dont understand how that would develop so quick.

If its lifter, should i not feel play when checking the rocker arms?

 

[strutaeng]

That to me sounds rather like rod knock. A lifter tick is a cycle half of the engine RPM, and sounds similar like a diesel.

Have you drained the oil for inspection? Look for a glittery sheen on the oils drain pan. Also, remove the oil filter and cut it open to inspect the filter media.

 

[kjetilaf]

That to me sounds rather like rod knock. A lifter tick is a cycle half of the engine RPM, and sounds similar like a diesel.

Have you drained the oil for inspection? Look for a glittery sheen on the oils drain pan. Also, remove the oil filter and cut it open to inspect the filter media.

it is on my todo list,
so far i have done a compression test with all plugs out,
and one in the suspected area is reading lower. / 131 psi / 9 bar
the rest were reading 174 psi / 12 bars

with camera there is also signs of some scratches on cylinder wall, that can explain the lower compression, but does not explain the sound.


i am also heading for a bottom end / rod bearing issue here... maybe i should just drop the pan before deciding what to do next...

 

[rockola1971]

Holy Smokes! If that isnt a rod knocking then its a cracked flywheel. That does not sound good at all.

 

[Mudsport96]

Could be a cracked flywheel like Rockola said. In your first post you said it made a noise when trying to start it. What kind of noise?
Could be a rod knock.
What caught my eye was the HORIZONTAL mark in the cylinder.

That looks like the mark a ring makes when an overheating engine is shut off and rings seize until the engine cools. Have you ever overheated it?

 

[kjetilaf]

Could be a cracked flywheel like Rockola said. In your first post you said it made a noise when trying to start it. What kind of noise?
Could be a rod knock.
What caught my eye was the HORIZONTAL mark in the cylinder.
View attachment 454751
That looks like the mark a ring makes when an overheating engine is shut off and rings seize until the engine cools. Have you ever overheated it?

It has not been overheated as far as i know, but i am 6th owner of this one, so i cannot speak for what has happened earlier

For me, the noise at startup was like a kickback in 450cc dirtbike. I suspect an leaky injector to be the culprit to that, but it seems odd to me the knock develops after this. It was just starting when it stalled with some sounds, hard to describe. I just restarted it like normal, and there was knock that never went away

I disabled the suspect cylinder, unplugged coil and injector, and the noise got better so i could move it to my garage. I will have to source a new engine, but i will pull the pan first. Will let you guys know what i find.

Before i went to work, i used this car and a trailer to bring an X5 home. Approx 460 miles / 740km both ways, without a fault. Used the car for some small errands after this, parked for 14 days, boom knock.

 

[rockola1971]

Leaky fuel injector could mean bent rod.

 

[02_Tahoe]

It has not been overheated as far as i know, but i am 6th owner of this one, so i cannot speak for what has happened earlier

For me, the noise at startup was like a kickback in 450cc dirtbike. I suspect an leaky injector to be the culprit to that, but it seems odd to me the knock develops after this. It was just starting when it stalled with some sounds, hard to describe. I just restarted it like normal, and there was knock that never went away

I disabled the suspect cylinder, unplugged coil and injector, and the noise got better so i could move it to my garage. I will have to source a new engine, but i will pull the pan first. Will let you guys know what i find.

Before i went to work, i used this car and a trailer to bring an X5 home. Approx 460 miles / 740km both ways, without a fault. Used the car for some small errands after this, parked for 14 days, boom knock.

If it’s got a leaking injector and leaked enough it could’ve hydrolocked one of the cylinders. If it had already fired on another cylinder before the piston in the cylinder with a leaky injector came up then it would definitely be enough to force the crank around resulting in a bent rod. Seen it happen on engines with a bad head gasket that allowed coolant into a cylinder. Can’t compress a liquid

 

[rockola1971]

If it’s got a leaking injector and leaked enough it could’ve hydrolocked one of the cylinders. If it had already fired on another cylinder before the piston in the cylinder with a leaky injector came up then it would definitely be enough to force the crank around resulting in a bent rod. Seen it happen on engines with a bad head gasket that allowed coolant into a cylinder. Can’t compress a liquid

Yep. OP definitely got some things to check out. I would drop the pan at this point and spin engine over and thoroughly inspect the bottom end rotating assembly.

 

[kjetilaf]

Yeah, i bet this engine is toast, with the low compression + knock, i dont see it smart to rebuild with the machining needed.

With a new block, i will also replace the injectors since it is likely thats the culprit, coolant level is and always have been stable.

Hopefully the heads can be reused