I have a 2000 Chevy blazer with 68000 miles on it. Over the past couple of weeks I am hearing a tapping/rattle coming from the engine. When I first start it in the morning it is very loud and after a few minutes it will get quieter. When I start driving it is more like a light tap (lifter). I thought it was a bad lifter so I took the top of the engine apart except the heads. All lifters were replaced. No bent push rods or rocker arms. Put it all back together changed oil and filter started the engine and same thing. I just read the GM up date talking about the timing chain replacement. The local dealer has the replacement chain set that comes with achain tensioner that is made to solve this tapping/rattling Caused by the balance shaft. It is worse in drive than it is in neutral and can really be heard in the RPM rangebetween1500 and 2500.Some times you don't hear it at all. The GM update that I read didnot say any thing about the rattle/knock at cold engine start up. I have donesome other thing that I was told to try like removing plugs wires one at a time Marvel oil different oil and filters and nothing has helped.Has any one done one of these timing chain retro fits and did it fix the problem.How much oil should I see comming out of the push rods after the engine is @ operating temp and @ 600 RPM's with valve covers off?

Can any one help with this.

 

There is also the possibility that a cam lobe has wiped, causing a lifter to be loose. This can be verified by wiggling the rocker arms. With the design of the rockers being non-adjustable, there is no way to take up this slack if present.

From your description, it is possible that the TSB on the timing chain and tensioner would fix your problem.

 

Thanks, I will look into the cam shaft and post my findings.