pvfjr

I was directed here for some more expertise by the guys at CK5.com.

I just bought a '04 Silverado from an insurance auction that was rolled. It's got 120k on it, and seems like a solid ride. It drives nice, aside from all the dents and broken glass. I was down with all the body damage, but this thing seems to have engine issues that they chose not to disclose.

I've read up on it, but I keep finding references to people saying that "all the 5.3's suffer from piston slap, it's normal."

I don't think this is piston slap though. It's not limited to cold starts, and it does it consistently all the time. I probed around with a $3 stethoscope a bit, and it doesn't seem to be coming from the top end. I hear it a lot around the bottom of the block. I'm pretty sure it's the loudest coming off the oil pan, but maybe it's not a good place to listen. Does it being broad and thin give it the tendancy to amplify the sound? It sounds fairly prominent in the waterpump housing too.

Oil pressure is fine, and the noise is consistent at all temperatures.
Power is good, and it runs quite smooth aside from the knock.


I'm guessing it's rod knock. What do you guys think? How can I troubleshoot this without wasting a ton of time or money?

Here's a little video so you don't have to listen a lot of description. The video does make it sound a little worse than it does in person.

gagliano7

I would think that is more than piston slap. When you rev it does the sound follow?

sreve

iTrader: (3)

does your stethoscope have a needle? With the one I have I can listen to each
bearing at the pan. Press it against the pan and move it forward about an inch at a time.
Makes me wonder if when it went on its side that the engine was still running for some time.

pvfjr

Yeah, it follows with engine speed. Does it in or out of gear, no change there. I've heard a few suggestions about a loose torque converter or a cracked flex plate, but I would think that would make some sort of change when a load is put on it.

My neighbor is convinced that it is a lifter, but I'm not so sure. I really think it would sound louder up top if it was.

pvfjr

Yep, it has a needle/probe attachment. I'm not sure if I can distinguish between bearings, but I can give it another shot.

BattleSausage

iTrader: (3)

If it was rolled, I'm willing to bet it was oil starved at some point. It definitely sounds like a rod knock to me. Funny thing about engines is sometimes it'll run quite a while like that or it make take a **** tomorrow. Have you tried disconnecting the plugs one at a time. You should notice a change in the sound when you disconnect the cylinder with the spun bearing as it won't have near the compressive forces exerted on it. Just hope you don't have several

pvfjr

That's a great idea, I'll try pulling plug wires while it idles today. It's funny you're the first to suggest that, seems like it would be an obvious step in troubleshooting. It does seem to be getting gradually worse. I think maybe the journal is scarred up too, and it just keeps making more clearance.

pvfjr

Well I tried disconnecting the coil packs one at a time, and no discernible change to my ear. Does that mean it's not in the bottom end?

RockinWs6

Unfortunately aluminum engine noises are tough to pin down. I would say if the noise didn't change pulling the coils its not a bearing. How does the oil look when you drain it? Try cutting the oil filter open too.

I had a similar experience that I would have sworn was a bad bearing that turned out to be a spun lifter.

You could pull the valve covers and carefully measure the lift on each rocker, this will usually show something if there is a problem.

But I hate to say it, sounds like a rod bearing to me. Heads gotta come off for a lifter anyway, why not pull the heads off and inspect the lifters etc. If its not the lifters you know its bottom end and you really didn't spend anything extra.

pvfjr

Well the head gaskets aren't reusable are they? If I pull the heads and find nothing, I don't want to have to buy new gaskets just to put it back together again. Not to mention the head bolts...

And unfortunately, I don't really have a good place to work on this thing. I'm living in a mobile park while I go to school, and we're not supposed to do any serious work on vehicles here. I could probably go as far as pulling valve covers or heads, but I definitely wouldn't be able to pull the engine here.

I have an acquaintance who would allow me to use his garage for a day if I needed to do a motor swap, but it's not a place where I can tear something down and leave it for a while. And it's across town, so if I tear into things too far here, it may be difficult to move the truck over there to do a swap. I'm not sure how to proceed.

On another note, my wife changed the oil herself when we got this, so I'm not sure how it looked.

RockinWs6

Then roll the dice and drive it.

pvfjr

So if I pulled a valve cover and measured the rocker movement, what exactly am I looking for? Would there be a very pronounced difference in movement for a rocker that had a collapsed lifter? Would I be able to find play by hand inspection?

RockinWs6

You measure the lift, a worn broken lifter will be different than the rest. With that much noise if its a lifter it should be obvious.

RezinTexas

the LM7 is iron block

Head bolts and gaskets are definitely not re-usable in your situation.
I agree with rockin, just pull the heads and inspect everything, including lifters.

pvfjr

Rob WS6

iTrader: (16)

Oh damn! I bet that cylinder got hydrolocked at some point.

RezinTexas

took me a minute, then I saw it. Damn!

Sorry for your troubles, but at least now you get to upgrade...

Old Geezer

iTrader: (3)

Like some moron tried to start it, when it was rolled back onto the wheels, after the wreck...Oil ran past the rings, partially hydo'd it.
A common problem.
[Just saw a NICE, lo mile 07 Silvy, w/ 2 rods out of the block....Same stupid mistake.]

Rob WS6

iTrader: (16)

Yeah, ya know that would probably make the most sense. That's a shame, but at least it didn't take the whole block with it.

pvfjr

Yeah, as soon as I saw that rod I thought "Oh no they didn't...". When will people learn? How hard is it to try turning it by hand first just to check? Then pull the stinking plugs and crank it over? Grr....

Oh well. I ran out of daylight last night, so I'm going to pull the rod cap off and see what the crank looks like today. Hopefully it's not scarred up, but that twist in the rod has been putting a little side load on those two rod bearings.