mwe625

i have a 2002 z-71 and for the last 3 to 4 months when i crank it for the first time in the morning the valves rattle for a few seconds and then quits. but when i drive it for a while and turn it off and then turn it back on it wont rattle. any ideas in what the cause of this might be and how to fix it? thanks for the help....

mwe625

tykrz

lifters leaking down or sticky. Try changing oil and putting in some oil conditioner. Another trick is to put in about a 1/2 litre of Dexron ATF with your next oil change. If that dont fix it you'll have to change the lifters

mwe625

tykrz,
thanks for the info about my problem. after posting my question i ran into a friend of mine who is a mechanic and i mentioned to him my problem. he said GM was having problems with my style of truck in which using alot of regular gasoline is causing deposits to form on top of the pistons which is causing my rattle problem. does this sound like something you might agree with. he said i needed to take my truck to a garage that could clean my injectors and this would solve the problem. anyway, thanks for the advice and i will wait for your reply before doing anything.

mwe625

GMMerlin

Is this a ticking noise or a knocking noise?
On the Gen III engines there is a condition people refer to as "piston slap" which is a knocking noise heard on cold starts that usually lasts between 5-30 seconds.
This condition is caused by carbon deposits on the piston. When the deposits are cold, the carbon is hard and will cause this noise..once some fuel and heat are added to the carbon, the noise goes away.
The carbon will not cause damage, but it is a disturbing noise to hear from your engine.
Using octanes higher than recommended can cause carbon deposits to form (higher octane fuel burns slower and in low compression engines will leave deposits).
Cleaning the injectors will not help..what needs to be done is the engine will have to be decarbonized.
This is a specific procedure outlined in GM Service Information that will remove the carbon deposits.
This procedure along with using only Top Tier gasoline and insuring that your vehicle regularly reaches operating temperatures will reduce the chances of this happening again

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tykrz

I don't buy the carbon deposit theory on piston slap. I've had that procedure done in the past several times by dealers under warranty to with no results.
My new 2005 exhibits this problem and currently has 2500 miles on it and is 2 months old .It has had piston slap since the day I bought it. No way an engine gets carboned up from the factory in that short order. The last 2 GM products I owned also exhibited this problem all from day one. From what I've been told is the problem is a design flaw in which the piston destabilses due to clearance tolerances between the piston and cylinder.

GMMerlin

The newer engines (GEN III) have a skirtless piston design also.
Not to sound like I am contradicting myself on what is going on, but there are 2 possible senerios here regarding "piston slap"
1. Carbon...usually starts after 12-15000 mikes
2. Piston to cylinder wall clearance.....there has to be some clearance between the piston and the cylinder wall...as the engine componants heat up, the clearance is taken up..this is a manufactured tolerance and I personally have not seen any GEN III engines that exibited any damage from this.
I have many customers with 200K to 300K miles on their GEN III engines with no internal engine concerns and my GEN III engine has 90K on it and I am satisfied with it.

__________________
Why do you never have enough time or money to do the job right the first time, but enough time and money to do it again?
Got all the certifications
25 years ASE Certified Master Technician
GM WCT
Yea..I work at a DEALERSHIP....got a problem with that?

Want to diagnose cars like the Pros? FOR SALE: OTC Perception 2 channel Labscope (badged as a Matco Reality)
This is my personal labscope that I use to diagnose waveforms, like new, comes with leads and training video
PM Me for details

mwe625

[thank you for your help in this problem of mine. to answer your question, it is a combination of both but more a ticking noise that knock. this noise happens when i crank my truck in the mornings and only last for a few seconds so your reply answer sounds dead on. my friend told me it was a problem that gm has had on this type of motor. you said i needed to get my motor decarbonized, how is this procedure performed and would you know the cost of the procedure? thanks again,

mwe625

QUOTE=GMMerlin]Is this a ticking noise or a knocking noise?
On the Gen III engines there is a condition people refer to as "piston slap" which is a knocking noise heard on cold starts that usually lasts between 5-30 seconds.
This condition is caused by carbon deposits on the piston. When the deposits are cold, the carbon is hard and will cause this noise..once some fuel and heat are added to the carbon, the noise goes away.
The carbon will not cause damage, but it is a disturbing noise to hear from your engine.
Using octanes higher than recommended can cause carbon deposits to form (higher octane fuel burns slower and in low compression engines will leave deposits).
Cleaning the injectors will not help..what needs to be done is the engine will have to be decarbonized.
This is a specific procedure outlined in GM Service Information that will remove the carbon deposits.
This procedure along with using only Top Tier gasoline and insuring that your vehicle regularly reaches operating temperatures will reduce the chances of this happening again[/quote]