CSK / knocking / rattling...

Daubs · May 17, 2006

I've got an 04 CC with 8.1/Allison ~27k miles. Knocked when started in morning. Took to my dealership and they removed spark plugs, squirted in some cylinder cleaner, let sit overnight, then cleaned out, installed new plugs and sent her home.

Did not help the cold start knock. If anything, made it worse. My truck knocks when you start it at any point in the day. As long as it has sat for 25-30 minutes or more.

And it also rattles around 1,800 - 2,000 RPM under light load.

Arrrgggghhhhh....

Took back to my dealership (whom I really like and respect). They looked over again, talked with GM, and sent her back to me without doing much. Dealer said he would cover the engine even after warranty is over, which gives me a little peace of mind. But I'm still left with the incredible-knocking-truck. Frustrating.

As said before, I really respect the dealership I've been working with. This is my fourth new purchase/lease from them since 1999, and they treat me and the Mrs. very well. Have covered many things that weren't under warranty, loaners for weeks at a time, great prices, etc. So I don't want to screw them. But I'm frustrated that GM won't do anything to solve this problem (gee, I feel like the many 5.3/6.0 owners who have been crabbing about this issue for years).

Any one or anything I can do to help get this solved? Suggestions??? Thanks, D.

GSchretter · May 17, 2006

Shot I thought all chevy v8 engines did that.

One thing that I did that fixed my knock was a high volume / pressure oil pump.

I guess one of the bearings knock for a few minute until the oil warms up and fills in all the gaps..

My other truck does it about every 10 start.

Now I got that missing from the EGR vavle opening around 1500 to 1800 rpm.

Truck skips pretty bad on the highway,.

Supercop8100 · May 20, 2006

Its called piston slap. Its been talked about on here forever. It does not hurt your engine. My truck is a prime candidate for it and it doesnt do it. No biggy, sounds like a diesel right?

You have one of the best trucks on the road today. Dont let something minor like that irritate you.

Daubs · May 21, 2006

Its called piston slap. Its been talked about on here forever. It does not hurt your engine. My truck is a prime candidate for it and it doesnt do it. No biggy, sounds like a diesel right?

You have one of the best trucks on the road today. Dont let something minor like that irritate you.

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I know. But doesn't change the fact that I hate it. And would really like GM to do something about it. HOping that someone has actually had GM fix this problem for them...

Supercop8100 · May 22, 2006

THey have. They replaced the factory oil pump with a high volum pump and it makes the slap gp away.

So there.

Daubs · May 22, 2006

THey have. They replaced the factory oil pump with a high volum pump and it makes the slap gp away.

So there.

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Thanks, that will be something to ask my dealer-guy and the GM service rep.

Wait, are you saying GM now installs high vol oil pumps in new engines? (if so, when did they start?) Or new pump is a fix that i need to request?

Haulin' 8.1 · May 22, 2006

Piston slap isn't related to oil volume or pressure.

Vernon

Daubs · May 23, 2006

Piston slap isn't related to oil volume or pressure.

Vernon

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There goes that glimmer of hope...d**n.

Jacqson · May 23, 2006

Piston slap isn't related to oil volume or pressure.

Vernon

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Yeah, I was kind of wondering that myself. I couldn't figure out how a high volume oil pump would correct Piston Slap.

Haulin' 8.1 · May 23, 2006

What is happening there (CSK) is that as the crank throw for a cylinder passes the top of it's travel the piston rocks over like a teeter-totter switching sides and clanks agaist the bore when it runs out of slack. You usually only hear it on the power stroke as this is when cylinder pressure is high enough to generate a loud noise when it rocks. As long as the noise goes away as the engine reaches operating temperature this is normal. The pistons expand a certain amount as they heat up. So the engine designers set clearances so that at full expansion the piston will fit just right. In piston technology metals that expand the most are stronger than those that expand very little. So it's not that GM is using cheaper pistons that in your passenger car, in fact it's just the opposite. In order to provide a stronger piston for your hard working truck engine they used a high expansion strong alloy that will fit a little loose when cold. Obviously a Malibu doesn't experience the load that a truck will so designers can get away with a weaker low expansion piston that fits tigher when cold. Therefore when Sally safe driver loads up the kids and heads off to Wal-Mart for groceries she hears only the A/C blowing full blast, and her kids trying to yell over the stereo. No piston rock noise to cause any undue anxiety. Very important point here --> normal for a car and normal for a truck are two different things.

Now the same "piston rocking" noise can indicate a real problem when it doesn't go away at full operating temperature. That would indicate a worn out bore, cracked or undersized piston, or similar. If it is something that develops all of a sudden expect engine damage, if it develops slowly over many miles of use it could be time for a rebuild.

To add to the mix I've also witnessed confusion here over CSK and valve train clatter on start-up. This is a dense light clatter on most any start-up that is usually caused by a cheap or defective oil filter or incorrect oil wieght. If the filter lets the oil drain back through it on shut down your vavle train will develop excessive clearance as soon as it's put back into motion causing much noise as the valves are cycled open and closed. Once the pump has had enough time to repressureize the entire engine the hydraulic lifters will pump back up and remove all the slack. This usually takes only a few seconds, though occasionally a lifter will stick down and may or may not pump up for any length of time leaving a click. If the clatter noise doesn't go away within twenty seconds or so shut the engine off and check your oil and look for a oil delivery problem.

Vernon

Scyry · May 23, 2006

Mine was so bad I could here it, from the curb, inside my house 20 feet away when I would start it on a cold morning. Would last until the truck warmed up, would slowly quiet as the motor warmed up but was really loud for the first minute. Was "normal" according to every dealership I took it too. My solution, sell the embarassing POS.

Daubs · May 23, 2006

Vernon: Based on information about my 8.1...

- rattles / knocks every time you start it (provided it has sat for 20-30 minutes or more)

- rattles in the 1,800-2,000 RPM range under light load

What is your assessment?

By the way I've now left two messages with GM customer care team. I was told they would review my case and get back to me last Friday. Oops, dropping the ball on that one...

Haulin' 8.1 · May 24, 2006

Well it's not that easy to diagnose things but it's a likely canidate for excessive cylinder to bore wear. You should have a leakdown type compression test done. Proving excessive wear, that it's worn out, under warranty along with adequate maintainence is your only option for them to repair it.

Vernon

Daubs · May 25, 2006

Update:

Finally got through to GM's customer service department. New woman working with my case. She asked to place me on hold and called my dealership. Came back on the phone and said my dealer would call me soon to set up appointment to see my truck again. She also said GM would be sending me out a letter covering me for 12 months from today (truck has 29k miles on it right now). If problem persists they will issue more 12 month letters.

Dealership called literally minutes after I got off phone with GM (they really are great guys). We went over previous visits. Said they did do compression check in previous visit and it was a-okay. Talked about the procedure to get carbon build up off the pistons (that didn't solve rattle / knock...probably made worse).

He wants to have look and listen again and check cylinders with bore scope.

If they can't isolate the problem the next step after that is pulling engine and tearing her apart. He did warn that they have torn apart and put new pistons in 8.1's, only to have them knocking again in the future.

It's going in next Tuesday. I'll post information as it becomes available.