Engine knock

[east302]

This is on a 1998 K1500, 350, 230k miles.

Earlier this year (7,000 miles ago) the #5 hydrolocked due to a cracked head. The other head was also cracked and I replaced both.

It’s my son’s truck so I rarely drive it, but I noticed a knocking sound a week ago. Changed the oil (5W30 Mobil 1) with no change.

Attached are videos of it. It only does this when warmed up. When cold, it’s quiet and gauge shows oil pressure of 40-psi. As it warms up, the knocking is louder and oil pressure is about 20-psi. I’ve not verified with a mechanical gauge.

The noise increases with engine speed, becoming so fast as to be hard to hear past 2000-rpm. It does the same when in gear.

So, can y’all suggest a next step on diagnosing this? I’d thought of pulling the intake and swapping the lifters, but it’s not really a ticking and the noise seems louder when heard from below - particularly on the oil filter side.

I readjusted the valves with no change.

 

[iamdub]

It's difficult to tell from these types of videos. Between the sounds in the videos and your symptoms of it happening only when warmed up, I'm leaning towards a lifter collapsing. I'm thinking the oil thins out when warmed up and the weak lifter collapses. You could try 20W-50 and see if there's any improvement. Maybe even try some Motor Honey just as a diagnostic measure. Since you just changed the oil with Mobil1, you can drain it into a clean container to put back in later. If it were me, and if I were pretty sure of the side, I'd pop off that driver side valve cover and look for a loose rocker arm.

 

[east302]

Thanks dub.

From above, it sounds more prominent on the right bank but using a stethoscope on the valve cover it didn’t sound louder in any particular area. I pulled the cover earlier today and none of the rockers were loose (engine not running and shut off for maybe five minutes after running). I’d love for it to be lifters. Would it be visually obvious with it running?

In the back of my mind is a concern that bearings are damaged after the cracked head and hydrolock. There was definitely coolant in the oil after that jamboree.

 

[OR VietVet]

If you pull the plug wires, one at a time while running, the noise change should narrow down the cylinder effected. I know that typically is to narrow down a rod knock, but it could change for a lifter, in a small way. It is worth a shot. It does sound like a lifter to me though, but I am old. Good luck

 

[iamdub]

Thanks dub.

From above, it sounds more prominent on the right bank but using a stethoscope on the valve cover it didn’t sound louder in any particular area. I pulled the cover earlier today and none of the rockers were loose (engine not running and shut off for maybe five minutes after running). I’d love for it to be lifters. Would it be visually obvious with it running?

In the back of my mind is a concern that bearings are damaged after the cracked head and hydrolock. There was definitely coolant in the oil after that jamboree.

Right bank? I was thinking the oil filter was on the left side. That's why I said driver's valve cover. My mistake. Regardless, you already pulled the cover.

It might be obvious when running, but it'd be really hard to see. They flick too fast. Also, you'd have a dead or really weak cylinder if it was collapsed enough to be visually obvious.

I like @OR VietVet's suggestion of killing cylinders until the sound changes. This would at least point you to the cylinder.

On that note, have you verified all spark wires were secure and all plugs were tight? A spark jumping a gap can "tap". A loose plug can make a similar sound that can change with temperature due to the metal expanding. This doesn't explain the drop in oil pressure unless it's affecting the idle enough to lower the RPM that much.

 

[OR VietVet]

When you pin point the cylinder, do a compression test.

 

[east302]

Right bank? I was thinking the oil filter was on the left side. That's why I said driver's valve cover. My mistake. Regardless, you already pulled the cover.

It might be obvious when running, but it'd be really hard to see. They flick too fast. Also, you'd have a dead or really weak cylinder if it was collapsed enough to be visually obvious.

I like @OR VietVet's suggestion of killing cylinders until the sound changes. This would at least point you to the cylinder.

On that note, have you verified all spark wires were secure and all plugs were tight? A spark jumping a gap can "tap". A loose plug can make a similar sound that can change with temperature due to the metal expanding. This doesn't explain the drop in oil pressure unless it's affecting the idle enough to lower the RPM that much.

Sorry about that, from above it sounds like it’s coming from the right bank but from underneath it sounds slightly louder-ish on the left. It’s just not as obvious as I wish it were. Going to go listen again and check the plugs.

It shows slight (2 to 6) current misfire counts on #2 when running which may have predisposed me to think right bank.

The oil pressure has been low for some time now even before all of this.

@OR VietVet I’ll pull some plugs when running. Also have a compression tester.

 

[OR VietVet]

I am sure you meant to say "pull plug wires" and not "pull plugs". Pull plug wires first, one at a time, to try and locate/pin-point the effected cylinder. Then pull all plugs to do the compression test. When you pull the plug wires, you can do it at the spark plug a or at the cap, whichever is easier.

 

[tom3]

If not discovered to be a loose plug or exhaust manifold leak I'd go with a thicker oil to start with. That old school small block might not like that 5wt, syn. oil when cold. 15w40 Rotella or the 20w50 mentioned above might do the trick. That's pretty high miles on that machine.

 

[iamdub]

Sorry about that, from above it sounds like it’s coming from the right bank but from underneath it sounds slightly louder-ish on the left. It’s just not as obvious as I wish it were. Going to go listen again and check the plugs.

It shows slight (2 to 6) current misfire counts on #2 when running which may have predisposed me to think right bank.

The oil pressure has been low for some time now even before all of this.

@OR VietVet I’ll pull some plugs when running. Also have a compression tester.

This is actually an upside, diagnostically speaking. Check that #2 spark system- the wire (both ends), the plug, etc.