2.8 knocks only at idle, only when warm - Team Camaro Tech
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post #1 of 4 (permalink) Old Oct 20th, 02, 07:34 PM Thread Starter
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Join Date: May 2001
Location: Michigan
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Hello all,
I've got a 2.8 V6 with 105K miles. I've owned since new and always changed the oil every 3 to 4k. Never any problems with it until last year when I had a cam exhaust lobe go and changed the cam and lifters, timing chain and gear while I was in there. Everythings been great for the next 7k miles. Now I've developed a knock. Only at idle and only once the oil is up to temp. I rev it to 1500 and the knock goes away. It's definitely not a valve train knock, I'm certain it's in the bottom end. I pulled the serpentine belt off to eliminate all the accesories, checked out the rockers, pushrods, ect. The stethoscope seems to lead me to the block, not the heads. Car runs great, makes no noise going down the road or anytime when it is cold. Oil looked great as did the filter when I cut it open. Oil pressure is low when warm at idle in gear, about 15psi at 900-1000 rpm. The knock isn't constant it comes and goes radomly when idling. I'm hoping the bearing clearnaces haven't opened up enough to be causing this, I would hope with only 105K and frequent oil changes over the last 13 years this wouldn't be the case already. My plan is to put a direct gage in place of the sending unit to verify the factory gage and sending unit are fairly close to correct, then pull the pan and replace the pump and pickup and check the bearings. It's a pretty easy job to do, just want to make sure no one else has had any experience with this before I go ahead with it. Can anyone think of anything I might be overlooking?

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post #2 of 4 (permalink) Old Oct 21st, 02, 03:05 AM
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I would pull the plug wires one at a time to locate the Rod(?) bearing knocking, piston slap, or main bearing knocking.

I would suggest when viewing the bearings, measure the journals for size, just to make sure they are still round, look at the backside of the bearing shell for size and replace them with new ones. You're already there.

Replace the rear main seal, of course. Use plenty of GM's EOS.

But, before doing anything, I'g try a can of GM'S EOS in the crankcase.

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post #3 of 4 (permalink) Old Oct 21st, 02, 05:59 AM
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You may have been setup for bearing failure since the cam went bad. Even one lobe could loose enough metal into the crank case to cause further problems...

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post #4 of 4 (permalink) Old Oct 21st, 02, 05:53 PM Thread Starter
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Thanks for the replies guys. Everett I'll try the oil supplement and then try to isolate it to a particular cylinder if it's still knocking. I'm pretty certain it's only one, at least right now. The way these things go if ones bad, there are probably others on the way as Dennis suggested the cam lobe particles went somewhere, I'm sure through the entire oil system. If the crank looks good the bearings would be a good idea while I'm in there as well. Dennis I was surprised that the #5 exhaust lobe was practically gone down to the base circle, and it still ran fine except for a popping through the exhaust under a load. Most of the other lobes were severely pitted especially near the top of the ramps, so they were on their way out as well. I had hoped I was going to get away with just a cam change, or so it seemed for the last year. Well my weekend seems to be planned for me now! At least I can put off replacing that torque converter control solenoid for another week!

Thanks guys for you input. I sometimes get into a denial stage with these things where I just don't want to believe it to be as bad as it really is, until I've eliminated everything else. It helps to have others ideas to kind of reinforce what needs to be done.

Thanks again,

[This message has been edited by SY1 (edited 10-21-2002).]
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