Trailblazer is knocking

Hello everyone,
my Trailblazer (2002, 32.000kms) developed a kind of deep-sounding, distict knocking that seems to come right out of the bottom of the engine. No
metallic 'pinging', more like a thumping. It can be best heard when I listen at the right front wheel-house just after starting the engine. It becomes quicker when I rev up the engine. It's even more distict during cold weather. After a minute or so, it just fades away. I use the best gas available. My dealer says everything is just fine. I am not so sure. The car is still on warranty. What makes the thing worse is that here in Germany nobody has the faintest knowledge about this car. Any help by you specialists? TIA Andreas
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It's called Piston Slap and is very common with the newer GM engines (especially the 8-cylinders). While annoying, it's nothing to worry about. Do a yahoo or google search for "Piston Slap" and have fun reading the kajillion results you get! Thisissue isn't just with GM, but also with Ford and Toyota products.
Doc

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Thanks for helping me, Doc. I did not know that the 6-Zyl inline engines could get piston slap too. I always thought that this was an issue of the 8 cylinder motors. But I never stop learning (:-; Andreas
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I goofed, AFAIK the I-6's aren't affected. Sorry!
Doc

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"Doc" wrote:

Actually, you didn't goof, Doc. The 4.2 does exhibit the piston slap noise that all the 3100/3400 and the newer small blocks do. They all seem to be noisy for the first few minutes of operation, but for whatever reason, nobody seems to complain about it. But it is there. I hear it everytime I drive them in off the lot.
In the case of this posters vehicle, he may just be hearing the normal noise they all make, but he should be getting a new engine because of the cracking sleeve syndrome. Eventually, it will break.
Ian
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wrote:

piston slap has everything to do with the design of the piston, not the configuration of the motor (i.e. I4, F4, I6, V6, etc)
-Bret
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A.Muewi wrote:

There is a problem with "some" 2002 Trailblazers. The cylinder liner can crack and cause extensive engine damage. GM actually has a "special policy" out on this.....and if your vehicle falls within certain VIN break points, they will install a new engine, once they have verified the problem. For your vehicle, the VIN breakpoints are from 22100007 to 22358861. Check and see if your vehicle VIN falls within that number range. I'll include the particulars of the special policy below.
Special Policy Adjustment - 4.2L (LL8) Bore Liner Cracking #03019 - (06/06/2003) 03019 - Special Policy Adjustment - 4.2L (LL8) Bore Liner Cracking Certain 2002 Chevrolet TrailBlazer; GMC Envoy; and Oldsmobile Bravada
Condition Some customers of 2002 Chevrolet TrailBlazer, GMC Envoy and Oldsmobile Bravada with 4.2L (LL8) L6 engine produced during the 2001 calendar year may experience cracking of an engine cylinder bore liner, resulting in engine noise, poor performance, and/or stalls with no engine re-start. Engine replacement is necessary to correct this failure.
Special Policy Adjustment This special policy covers the condition described above for a period of seven (7) years or 100,000 miles (160,000 km), whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership. The repairs will be made at no charge to the customer.
For vehicles covered by Vehicle Service Contracts, all eligible claims with repair orders on or after June 13, 2003, are covered by this special policy and must be submitted using the labor operation codes provided with this bulletin. Claims with repair orders prior to June 13, 2003 must be submitted to the Service Contract provider.
Vehicles Involved Involved are certain 2002 Chevrolet TrailBlazer, GMC Envoy and Oldsmobile Bravada model vehicles equipped with 4.2L (RPO LL8) L6 engine and built within the following VIN breakpoints:
Year Division Model From Through
2002 Chevrolet TrailBlazer 22100007 22358861
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Bingo! It does. But I didn't notice any loss of power so far. Do the engines fail completey? When does this occur and how do I know when it's going to happen? I am not a "soft" driver and I like to travel at high speeds on the autobahn. Does this matter? I know, it's a lot of questions, but I like my Trailblazer and would like to keep it for a while. Thanks a lot for helping me. Andreas
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A.Muewi wrote:

After re-reading your original post, all that you may be hearing "at this point" is the normal piston noise that these engines make when cold. But, you do have the defective engine in that vehicle, and it should be replaced. I suspect that you may have to jump through some hoops to get the updated 2003 engine, but that's what you should be shooting for. To date, we've only seen one failure in our dealership, but I've heard from other GM techs around the city, that numerous engines have failed and been replaced. It's usually catastrophic when it does happen.
Take the number of the special policy that I quoted into your dealership service manager and sit down and talk with him about it. GM does cover the motors from failure for a long time, but I'd be trying to get a motor sooner then later.
If they do replace the motor, it's important that they follow the directions and switch over the oil pan, spark plugs, and knock sensors from your engine. The 2003 engine does not use an oil level sensor like your engine, and the other two items are probably due to some calibration issues.
Ian
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Ian (and, of course, all the others), thank you very much for your informative answer. Does this mean my dealer will have to change my engine even it has not yet broken down? Or do I have to wait till the pistons come shooting out? I do not want this to happen when I'm hundreds of kilometers away from my dealer. I often have to travel long distances and Chevy dealers are a rare breed in Europe. Andreas

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A.Muewi wrote:

Upon reading the special policy closer, it looks like you have to wait until the failure happens. It does say "engine noise" so that's where I would start. Complain about the engine noise, (which you've already done) and then bring this special policy to their attention.
GM should have sent you a letter about this special policy. Are you the original owner? If not, you may not get the letter. This is a small section of what they say in there.
What We Have Done To address the above mentioned condition, General Motors is providing owners with special warranty coverage. If this condition occurs on your 2002 Chevrolet TrailBlazer, GMC Envoy or Oldsmobile Bravada within seven (7) years of the date your vehicle was originally placed in service or 100,000 miles (160,000 km), whichever occurs first, the condition will be repaired for you at no charge .
Good luck.
Ian
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If it is piston slap try this website it may provide answers and actually has a sound byte that is pretty severe: www.pistonslap.com .
Take it to dealer soon.
Bruce Christian.

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