Ok so here is my problem and im stumped. This truck 2000 blazer 4x4 4.3 with 130,000 miles got overheated so i had to replace the heads cuz one was cracked so i just did both. Now the truck runs great and has good oil psi 60 cold and 20-40 hot at idle. Oh and i removed the serpentine belt and it still knocks so its not a accessory.

However when the engine gets hot it stats to knock at idle. It seems to get better if not go away at 2000 rpm and above. I thought the knock was a engine bearing and since it just started i decided to look at them. So after pulling the pan off the motor and inspecting bearings i didnt really see any major trouble. All the bearings looked ok some had slight scoring but none showing any coper at all. So since i was in there i went ahead and replaced rod and main bearings. Crankshaft looked good too and a quick measure with a caliper showed it still at stock diameter.

So after the bearing replacement with only the oil pan installed and differential still out i ran the engine and the knock is still there. with the engine cold it sounds pretty good. once it runs for 15 min or so the knock starts to get louder. If i hold the engine at a steady 3000 or so rpm i don't really hear it anymore. when i let off the gas it knocks again at idle. If it was a crank/rod bearing it should have changed with the new bearings.

When i listen with a stethoscope i cant really pinpoint it. It does seem louder towards the front of the pan but hard to tell. I also can hear it pretty well if i listen to the distributor cap and timing chain cover? I dunno where to go i kinda wanna check/change the timing chain but am tired of just ripping into stuff without knowing. Would a timing chain knock or slap? Its defiantly a knock and not a lifter tick. And would a timing chain stop knocking with higher rpms?

So i turn to the gurus here to ask what yall think? Possible timing chain? balance shaft? Im open to sugestions . Dont wanna assemble the front end yet in case i need to do a timing chain since i have full access to the oil pan right now.

 

Did you measure any of the journals when you had the bearings out?

Also, are you sure it is a knock and not a lifter tap?

 

I did not measure any main bearing journals. I assumed after looking at all the bearings that they were ok since it shows no signs of real problem on the old bearings.

The knock seems too deep of a tone to be a lifter but im gonna look into that more today. I know a valve train issue would make sense since i had that tore apart while replacing the heads. Gonna remove valve covers and look around. Do a remove the plug wires test and see what that shows. Also found a timing light test that is supposed to help tell if the knock is upper motor or lower motor?

Im just assuming that if it was lower motor it would do it all the time and get worse with engine rpm not better?

OK so here is what i did today.

1 warmed up engine till it starts its noise.
2 pulled one plug wire at a time and no change in noise.
3 measured timing chain slack and it appears its about 10 deg. although its very hard to tell since there are no deg markers on this engine only pointers.
4 put a timing light on the engine and it seems that when the light flashes the noise is there. If it was a bottom bearing i would expect the noise to be there twice as much.
5 made a recording of the the Engine noise . This is it idling for about 10 sec then reved to 2500 for 10 sec then back to idle for 10 sec. Recording was taked from the cross member under the harmonic balancer. The noise seems loudest int the front of the engine down in that area. Maybe itll help.

Im thinking since im starting to think its a valve train noise that i might as well change the timing chain anyways. I never put back together the front differential yet so i have full access to the oil pan. And it seems the pan has to be lowered again to change the timing chain. So this would eliminate that also but i have to work the next 4 days so itll be at least 5 days before i can do that.

Thanks fro looking and replying i hope you have heard this sound before and can help .

 

Just a update. I pulled the timing chain today i i believe the cam gear bolts were loose. I didnt take no effort at all for my air ratchet to bust them loose it didnt even struggle a bit. The gear behind the cam gear for the balance shaft has about 1/8 slop in it when on the cam. If i turn it hard back and forth it knocks and sounds alot like my trouble. I ordered a new gear set to see if it helps.

Anyone heard of that gear making noise before? It sure is sloppy and i dont like that. I have read up on a timing chain tensioner that can be installed do you guys think its a good idea to put that in while i have the chain apart?

 

It would definitely be a good idea to replace the tensioner while you have it all apart.

As far as slop in the balance shaft to cam gear connection, that shouldn't create any noticeable noise while running.

 

Well i give up. I have replaced the bearings and the timing chain and balance shaft gear. After replacing the balance shaft gear it seems to have changed pitch and quieted down some. However it is still there. Same as always it don't knock cold at all but once its heated up it knocks. Anyways im gonna drive it till it dies now and see what happens.

Thanks for any thoughts or advice you might have given.
Robert