99 Jimmy 4.3 4x4 engine rattle

I had the intake gasket replaced at 85k in 2/06, about a month and 1k miles later the engine developed a rattle above 1200 rpm and has gotten worse. The engine now has 94k on it. I took it to two chevy dealers and they both said it was a rod knock. I disagree because of the miles driven since the noise started. The knock-rattle is worse now, but the funny part is when the the engine starts when cold there's no noise. it's quiet and smooth. The oil pressure is good hot or cold, and it sounds more like the valve train than a heavy rod knock noise. When the noise first started I changed the oil looking for anti-freeze and found the drain plug magnet full of metal shavings. Now when I change the oil the magnet has nothing on it ,just normal debris. I just can't make a decision on weather to replace the engine or not because I'm not convinced it's a rod. thanks in advance.

Were the bolts for the intake torqued properly to specs? It is critical they are, or you will have problems like this. There was a TSB issued for this, you may be able to find it on here, I remember seeing it on here. Basically what it says is that if the intake was not torqued properly, or uneven torque values, it will warp, or twist the block, causing engine noise, and eventually engine failure. Usually the problem surfaces soon after the intake was replaced. Hope thats not your problem, but this to me sounds like it.

I would get it checked ASAP. I had mine replaced and a rattle started soon after and the engine went tits up soon after.


Don't know how I could have proved they torqued it wrong, though?

Yep, 96up lower intake is 12lbs and 95 earlier is 35 I believe and if you do the newer to that hiher value it destroys the crank due to block distortion

Isn't that nice of CHEVY:

Blow the gasket, loose the engine.
Fix the gasket (but slightly wrong torque), loose the engine anyway.

LOL...exactly, no win -win situation here.....:rofl:

I would get it checked ASAP. I had mine replaced and a rattle started soon after and the engine went tits up soon after.


Don't know how I could have proved they torqued it wrong, though?
The guy who replaced the intake gasket is a GM mech., he did the gasket as a side job in his garage. But like you say ,how can I prove it. this sucks.

a rattle can also be a timing issue or malfunctioning egr valve ( better known as pinging) the shavings on the oil plug could have come from the intake gasket job - its good practice to change the oil after doing intake gaskets - does this rattle happen even in neutral or park and the engine reved to 1200 ...

The guy who replaced the intake gasket is a GM mech., he did the gasket as a side job in his garage. But like you say ,how can I prove it. this sucks.


I talked to my companies mechanic. Basically, he would have to tear down the engine and see how it failed.



How long was the gasket leaking?

Its a always a possibility if you are lucky:
Just reread and a 99 - so you have the wonderful secondary air injection system so look at the 2 check valves feeding the exhaust manifold and the 2 rubber L hoses - they fail and burn thru giving an awful noise. Also if only a rattle check the PCV and see if its making the noise and often the throttle cable is contacting the PCV and ampfies the noise cause the plastic holddown to the intakes break off - resecure to intake with zip tie.

a rattle can also be a timing issue or malfunctioning egr valve ( better known as pinging) the shavings on the oil plug could have come from the intake gasket job - its good practice to change the oil after doing intake gaskets - does this rattle happen even in neutral or park and the engine reved to 1200 ...
The oil was changed when the gasket was done and a couple times afterward. This noise has been going on for 9k mi. It sounds like a lifter but the engine runs smooth, no miss. It just doesn't have that heavy hard knock that a rod would make. I don't know what the mech. torqued the manifold bolts to. The rattle happens driving or idling, neutral or park.
, no miss

Its a always a possibility if you are lucky:
Just reread and a 99 - so you have the wonderful secondary air injection system so look at the 2 check valves feeding the exhaust manifold and the 2 rubber L hoses - they fail and burn thru giving an awful noise. Also if only a rattle check the PCV and see if its making the noise and often the throttle cable is contacting the PCV and ampfies the noise cause the plastic holddown to the intakes break off - resecure to intake with zip tie.
Thanks, I'll check