GM 4200 knocking noise

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This motor as 199K miles and has been trouble free for the most part. I am getting a knocking sound at the cam speed but I don't think it's a rod knock..just a hunch.

What I have done is pull each coil lead and no change in noise. Changed oil and ran some Rotella T6 and 1.5 qts of ATF for about 150 miles, drained and refilled with Castrol Edge.

Did a water injection through vac line and also GM upper engine cleaner in hopes it was a carbon fouled chamber....also running BG44K.

Engine runs smoother but noise is still there. Noise is not audible on a cold start, takes 3 min to start making noise, get loud at roughly 5-8 minutes then gets quieter from there on out..about 60-70% quieter than at the loudest 5-8 min mark.

Did oil pressure test and pressure was very good, 25-30 PSI at idle but this was a sandwich adapter so I wasn't able to measure the pressure post-filtration.

I have had an occasional cold start tick for sometime and the oil change/cleaning has helped. The noise sounds like it comes where the head meets the block, I hear it more on top then under the vehicle but mostly from the drivers door...standing behind the LF fender but my attention is directed to the upper portion of the block.

Could this be a lash adjuster that is bad and ticks when cold? Could it produce a noise that's deeper than a tick but lighter than a knock?

I have nothing in the last two oil filters I cut open.

My harmonic balancer has the slightest wobble...barely visibly but I can see a very small deflection and I would guess .020-.030"

I have a thread going on this but was questioning a clogged filter screen, but I think dedicating it to a knocking noise may yield more results. http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/3341529/Re:_Can_I_backflush_an_oil_pic#Post3341529

Also, when I plug the large vac port on top the valve cover, after 30 sec the knock goes away.....very odd.

Also the noise seems to go away above 2-2500 and is most audible from the 600 RPM idle to about 1500 RPM
 
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Piston slap? Our motors are known for it. Mine is whisper quiet when running a thicker 5w30, but gets noisy when running thinner 5w30.
I won't run anything heavier than 30 weight because the variable valve timing relies on oil pressure at the cams to actuate the cam phasers. Proper flow is essential to proper functioning of the valvetrain. The 4.2 I6 is a tall motor. The oil has a long way to flow to the cams.
 
I doubt it's piston slap. i6pwr wrote that the noise starts after about 3 minutes of running. Piston slap is most audible when first started, and goes away as the pistons heat up and close clearance to the bores. Piston slap is also more audible from the bottom of the engine, not the top, where he says it's coming from.
 
Out of interest, what oil/filter combo are you using and is this a '02-'05 engine or '06-'09 with the MAF sensor? Did you pull the camshaft actuator solenoid to look at it?

Originally Posted By: salv
I won't run anything heavier than 30 weight because the variable valve timing relies on oil pressure at the cams to actuate the cam phasers. Proper flow is essential to proper functioning of the valvetrain. The 4.2 I6 is a tall motor. The oil has a long way to flow to the cams.


GM recommends anything from 0w-30 to 20W-50 for these motors here and they run forever. I personally run M1 ESP Formula 5W-30, which is a low SAPS oil that's essentially a 40 weight.
 
My grandmas 02' Trailblazer has this motor with 99k miles. Has had some piston slap on startup for 30 seconds tops for quite a while. Always taken care of, just the nature of the beast.
 
Originally Posted By: Falcon_LS
Out of interest, what oil/filter combo are you using and is this a '02-'05 engine or '06-'09 with the MAF sensor? Did you pull the camshaft actuator solenoid to look at it?


Motor is 02, late production and I don't believe it's within the cracked cylinder era of motors.

Haven't pulled the CPAS yet, but I will...it's about 3 years old and no oil in connector.

Also vacuum is rock steady at 20 inches at idle.
 
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