Knocking noise on intial movement for the day

[bthomas02tahoe]

I have noticed once my Tahoe sits overnight in the cold upon intial start up, and drive I hear a loud knocking noise from the engine.

The noice only lasts about 20 seconds or so then goes away, but I am wondering what this noise is.

Anybody know?

 

[HitandRunDriver]

It's piston slap and completely normal in tahoes, nothing you can really do about it

 

[2000Yukon]

nothing you can really do about it

Ya there is, spend alot of money and get it bored out. lol

 

[bthomas02tahoe]

It's piston slap and completely normal in tahoes, nothing you can really do about it

Why does this happen though?

It only happens on the first movement of the day. Should I let it warm up longer before driving?

 

[TnTahoe]

yeah a couple minutes should do the trick

 

[terrible_buddhist]

VERY common in those engines, and usually nothing to worry about...

Piston slap is caused when there's too much space between the piston and the cylinder wall. The piston moves up and down in the cylinder and the extra clearance results in a greater amount of rocking in the cylinder, producing a loud knocking noise. Vehicles with the engine knock problem include 1999 - 2002 GMC and Chevy pickups and sports-utility models with 3.1, 3.4, 4.3, 4.6 (Northstar), 4.8, 5.3, 5.7(LS1), 6.0 or 8.1 liter engines. Specific models include (but may not be limited to): Chevrolet Silverado, Tahoe and Suburban, GMC Sierra, Yukon and Yukon XL. The 2002 Cadillac Escalade SUV also reportedly suffers from the problem.

 

[Blkout02]

mine does the same thing good to know the hoe is okk

 

[badtothe bone]

Actually GM diagnosed this problem a long time ago to be a build up of carbon above the top ring of the piston.
At one time, while they were under warranty, the resolved the problem by taking out the pistons, cleaning them and reinstalling them with new rings.
In 40,000 miles, the symptoms reappeared.
If you look at the pistons you will see that the skirts are too short.
The way to increase power and mileage is to lighten the reciprocating mass.
By making the pistons, rods and crank lighter, you get more power and better gas mileage at the expense of a little noise during start up on cold mornings, due to the pistons not riding firmly in the bore.
So if you want to say that the pistons are too loose, your assumption might be right. But pistons are not round like the cylinders. They are actually oval and they grow as they heat up - so as to fill the cylinder as tightly as possible, yet be able to go up and down without galling and getting stuck when they grow.

 

[T3rry]

basically it just needs time to cycle the oil n stuff.

 

[TheFuzz]

Actually GM diagnosed this problem a long time ago to be a build up of carbon above the top ring of the piston.
At one time, while they were under warranty, the resolved the problem by taking out the pistons, cleaning them and reinstalling them with new rings.
In 40,000 miles, the symptoms reappeared.
If you look at the pistons you will see that the skirts are too short.
The way to increase power and mileage is to lighten the reciprocating mass.
By making the pistons, rods and crank lighter, you get more power and better gas mileage at the expense of a little noise during start up on cold mornings, due to the pistons not riding firmly in the bore.
So if you want to say that the pistons are too loose, your assumption might be right. But pistons are not round like the cylinders. They are actually oval and they grow as they heat up - so as to fill the cylinder as tightly as possible, yet be able to go up and down without galling and getting stuck when they grow.

Where did you get your information from? I've heard the whole carbon buildup diagnosis before, but it isn't accurate IMO. Think about it for a second...you're blaming a temporary ticking/tapping noise on a permanent condition (carbon buildup). If the noise goes away when the engine warms up a little, how could it be carbon buildup? A physical buildup around the piston rings would lead to a constant noise, don't you think? I've spoken to several GM master techs who dispute the carbon thing fervantly.

Here's my take on it, courtesy of one of those techs:

The reason you get the noise only when it's cold, is because the pistons are aluminum. Aluminum expands as it warms, so when the pistons are cold, there is a little excess room around the skirt (bottom) of the piston. After the pistons warm a little, they expand and the noise goes away. It's a simple and sensible explaination for a common problem. GM even introduced teflon coated pistons to help alleviate this problem, although the pistons didn't solve it completely.

In your example, the reason the noise went away upon cleaning the carbon out is because of the new rings they installed...not the cleaning. Once the new rings wear in a little, the noise comes back. The last part of your post was accurate though. It all has to do with the pistons expanding as they warm up.

 

[badtothe bone]

I experienced this problem way back in 2002 with a Avalanche with a 5/3 - Cast Iron Block and Aluminum heads.

The dealer I went to for repairs had the engine apart several times. We worked with the zone office out of Pittsburgh PA and the manufacturer provided me with a loaner Avalanche while they looked at the problem.

As a matter of fact, I had 3 different Avalanches, because GM refused to junk my vehicle under the lemon law. I spent more time in 6 different dealerships then what it took the Mexican's to put it together.

At 30,000 miles the engine started to use oil. Not just a little oil, but it got to the point of where it was using a quart of oil every 200 miles.

The engine in my 02' Avalanche was the test engine for problem solving.
It had the Mexican heads and GM paid for 16 new valves, 16 new guides, 16 new seats and a improved design valve seal.

In the end, it was determined that the design of the piston was at fault and that it would cost GM millions of dollars to repair the problem and that it caused no harm to the engine and to just keep driving it. At 150,000 miles, I finally traded in the Avalanche on a 2009.

Because I worked for several machine shops and a close personal friend of mine owns a engine shop. I can tell you with all honesty that when you bore a engine, you usually bore it to the size of the pistons and not to a standard number. The manufacturer will tell you what size the bore should be as per their instructions, how much the piston is expected to grow at operating temperature.

We usually bore it out to within .003 and then we hone it to the exact size within 1 or 2 ten thosandths.

Replacing the pistons would have solved the problem, but with 35,000 miles, the last time the engine was in for service, they felt that they had spent more money then what was alloted for that vehicle. Basically they were going broke trying to fix it.

GM also paid to replace the rear drive shaft due to a howl at 55 MPH.
They replaced all the bearings in the rear differential - which moved the howl up to 65 mph.
They rebuilt the front axle 3 times because of leaks, and then discovered that the leak was not caused by faulty bearings or seals, but by the synthetic oil in the differential.
They replaced the door speakers at least 3 times.
They replaced the radio once, the heater controls once, the instrament cluster once.
They refused to replace the cladding when it faded. My claim was the first for that condition.
They replaced the tailgate latch one time - because it would not stay closed in the cold weather.
They replaced the console lid when it refused to latch.
They replaced the saddle bag lid when it refused to latch.
They replaced the mid gate drain grate - when it refused to retract when you droped the mid gate.
They had to drill drain holes when the water leaked into the cabin.
They fought with leaky seams in the firewall.
The hinges were so bad that when you opened the back doors - it sounded like something from a spooky movie.

Calipers and rotors - more then you could count.

NO Brakes!

When I got rid of it, the rocker panels were rotted out because the people at the factory that assembled the cab did not open the drain holes when they put the seam sealer in the C pillars next to the floor and in the winter it was so full of water that the carpets in the truck were soaked and when you turned on the heater, the moisture from the carpets would steam up the windows so bad - you couldn't see out of them.

If there is something that could go wrong to a Chevy Truck, i have pretty much seen it all.

 

[TheFuzz]

That certainly sounds like a nightmare. Kudos to you for sticking with GM after all of that. Hows the GMT900 'Lanche working out for you? I've been eyeballing a black Z71.

 

[rdtahoe]

I have noticed once my Tahoe sits overnight in the cold upon intial start up, and drive I hear a loud knocking noise from the engine.

The noice only lasts about 20 seconds or so then goes away, but I am wondering what this noise is.

Anybody know?

Could be a lifter.

My 2000 5.3L LT has had a minor "piston slap" over the years, but oddly, it seems to have gotten better the more miles I have on it (at 105K Now). Seems to have gotten better when I switched to 0W-30 M1 at about 80K miles.

But, I have noticed in the past 8k miles what I think is a lifter noise after letting it sit for 4 or more days or so. I guess they're gettting a bit tired and need to "pump" up a bit if they sit too long.

Otherwise, the damn thing runs great @10 yrs, and 105K miles, and I've never done anything to the engine except new spec plugs (AC Delco Iridium) and set of wires at 100K service, and recommended coolant changes at 5 yrs (Dexcool), plus all other fluid changes per factory manual recommendations.

It's always had synthetic oil since new, changed at 3k intervals though the first 70K miles with premium filters (I use Purolator Pure 1), but went to 4 - 5K change intervals when I learned a bit more about the extended life properties of syn oil and good filters (can go as much as 10K miles according to some, but I just can't make myself go that far without a change!)

 

[puckhead]

The reason you get the noise only when it's cold, is because the pistons are aluminum. Aluminum expands as it warms, so when the pistons are cold, there is a little excess room around the skirt (bottom) of the piston. After the pistons warm a little, they expand and the noise goes away. It's a simple and sensible explaination for a common problem. GM even introduced teflon coated pistons to help alleviate this problem, although the pistons didn't solve it completely.
QUOTE]

This is the most common thing that I have heard and I would believe it. All our -degree days here and it take abouta minute or a block or so to get the metal warmed up and to its normal size.

 

[TheFuzz]

...I have noticed in the past 8k miles what I think is a lifter noise after letting it sit for 4 or more days or so. I guess they're gettting a bit tired and need to "pump" up a bit if they sit too long.

Otherwise, the damn thing runs great @10 yrs, and 105K miles, and I've never done anything to the engine except new spec plugs (AC Delco Iridium) and set of wires at 100K service, and recommended coolant changes at 5 yrs (Dexcool), plus all other fluid changes per factory manual recommendations.

Same here. Mine is a 2000 with 116K on the clock. Runs GREAT - but gets extremely pissed off at me at startup if I leave it sit for more than 3 days. That doesn't happen to often though. The piston slap goes away within a minute, usually...unless it's extremely cold.

Puck, remember that -15 cold snap we had a few weeks ago? Yeah, not good for my truck lol.

 

[puckhead]

Puck, remember that -15 cold snap we had a few weeks ago? Yeah, not good for my truck lol.

yeah, thats what its been the last few nights here! Starting to get into the cold of the winter. Its been warming up to high 20's during the day. So not too bad. You get any snow your way lately?

Makes me cringe when I hear the slap in the moring but I guess im gettin used to it. Just doesnt sound right!

 

[TheFuzz]

Not since last week. It was in the high 50s today finally! Then of course, it's so clear at night here that all of the heat vanishes as soon as the sun drops, and we get back down into the 30s within a half hour. Such is life in CO though.

How long do you let yours warm up before the slap goes away? Mine is usually gone in less than a minute, except for those occasional deep cold snaps.

 

[puckhead]

It seems like even if I warm it up it will slap until it is driven for a minute or so. I havent really paid attention though. I will have to listen closely next time. It doesnt take long at all though for it to be gone