V8 knocking sound Diagnose (video clip) (1 Viewer)

[alia176]

I'm hoping some one here can help me figure out the source of this nasty sound coming out of the 5.2 V8 (non Toyota engine).

I removed the valve cover and checked out all pushrods and rocker arms. Nothing unremarkable there. This sound does pickup speed with rpm and seems to be coming from the rear of the valve train but none of the rocker arms seem to be the culprit I don't think.

I'm tempted to remove the intake and see what I can find unless you guys have a better idea. Don't know if I want to remove the head yet.

Sure is nice and easy to work on a V8 vs the I-6. Easy access to everything

Thanks for any inputs.

Video

 

[SteveLCetc]

Did you do a compression test? Sounds kind of like piston slap. Did it come on all of a sudden?

 

[SteveLCetc]

Maybe a clogged pushrod. What's the frequency compared to the crankshaft? Kind of hard to tell in the video...

 

[pappy]

Bent pushrod? That sort of sounds like mine when I had the issue. Mine was a rocker out of adjustment, and the rod was bent.

 

[alia176]

Hmm, that's two people that mentioned bent pushrod. I took a cursory look at them but will do the "roll on a dinner plate test" tomorrow morning. It's been coming on for a while, softer sound in the beginning and now super loud. What gets me is that the sound isn't there always as in consistent right after engine turn over. Cool thing is that all parts I can get from NAPA; wow, what a concept!

 

[SteveLCetc]

I was thinking clogged *lifter* actually. One key is does it knock every revolution of the crankshaft, or every other? If it's a pushrod/lifter/cam problem, it will knock only every other revolution of the crankshaft, aka every time a rocker rocks. If it happens twice per rock it's not a cam controlled problem. Did you do a compression test?

 

[alia176]

Compression test #s:

cyl 1: 140
cyl 3: 145
cyl 5: 130 **** low ****
cyl 7: 137

cyl 2: 140
cyl 4: 140
cyl 6: 135
cyl 8: 130 (battery ran low, may not be accurate)

Mechanic stethescope revealed loud sound coming from #5 cyl area. Sound was really loud on #5 Intake rocker arm. Pulled that rocker arm and push rod out and ran engine. Still loud noise. So, it's safe to say that it isn't valve related. All push rods check out fine.

I moved to the other side of the engine and removed all pushrods and rocker arms and then ran the engine. Same sound.

Sorry Steve, I'm just not talented enough to compare the rev of the Cshaft vs the sound freq! I can't even find the IGN timing marks as the crankshaft pulley is buried under bunch of other pulleys.

If it's indeed the lifters, then I'll need pull the intake manifold which is WAY more involved than just pulling the head! Pulling the head will only reveal the combustion chamber which won't show me anything I guess.

I'm going to rent an oil pressure testing kit and run some more tests next weekend.

 

[SteveLCetc]

Pull the *exhaust* valve rocker and pushrod for #5 and check it.

What about cyls 5-8 compression tests - esp #5?

Watch a lifter at idle. Does it knock twice per lift or just once?

Where'd you get your mechanical stethoscope anyway? I used to have one but it broke and haven't found another one yet. It's a very good diagnostic tool.

Another thing to try is the pull-the-spark-plug-wires-and-check-the-rpm-drop test. Compare.

 

[alia176]

I update the cylinder numbers above. Looks like #5 has the lowest reading.

I moved to the opposite bank and removed all rocker arms and push rods and then ran the engine. Same noise. Noise seems to be coming from the center of the engine and then coming out of the valve cover areas so it's hard to tell the source of the sound.

 

[SteveLCetc]

Hmmmm. Maybe check the other bank compression and listen to those rockers? Could be the bottom end bearing is out on one of the pistons...

You could also get the oil checked. I'm not sure who does it in town now. The Komatsu place sends them out now.

 

[alia176]

It's sounding like the sound is coming from the bottom end. I can hear it quite clearly from under the oil pan. Might have to drop the pan and take a looksie although not sure what I'm going to find w/o the engine running.

Update above with remaining compression numbers.

 

[Cruisergreg]

Sometimes a certain cylinder doesn't get as much cooling as the others and if you're close to overheating you can round out the cylinder bore with the piston but not have much leakage past the rings. End result it a metallic tapping sound especially at idle. I had this on the 2F in my 60.

 

[Beowulf]

Where'd you get your mechanical stethoscope anyway? I used to have one but it broke and haven't found another one yet.

Harbor Freight Tools - Quality Tools at the Lowest Prices

$2.99 (Less than a Starbuck's coffee)

-Mike-

 

[SteveLCetc]

Sometimes a certain cylinder doesn't get as much cooling as the others and if you're close to overheating you can round out the cylinder bore with the piston but not have much leakage past the rings. End result it a metallic tapping sound especially at idle. I had this on the 2F in my 60.

AKA "Piston Slap".

Thanks for the link Mike.

 

[alia176]

Searching this topic is revealing that piston slap is more common on the 4.0 I6 engine but my problem may be a rod bearing. Assuming that the oil pan comes off easily, this maybe an easy fix....famous last words!!

 

[Albuquerque Jim]

I've heard/seen cracked flywheels make a similar sound. You can probably check that easier than pulling the pan.