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Old 02-04-2005, 09:15 AM
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My 6.2L has been making a slight knocking noise for quite some time now. I haven't really investigated it, because it was very faint and hard to hear. Lately, it's gotten a bit worse. Now it's starting to bug me.

I've narrowed it down to coming from the number 1 cylinder, I'm pretty sure, using the stethoscope method. It's not an injector, cracking the injector lines does not make the noise go away.

I first thought it was a lifter ticking, I've had that happen a few times. Usually a treatment of ATF in the engine oil for a few hundred miles makes it clear up and go away. Not this time. It's also louder than previous lifter ticks.

The other strange thing about this noise is that it sometimes goes away after warming the engine up. It's always present when the engine is cold, but sometimes after driving a while, I can't hear it anymore.

The noise seems to be coming from the top end of the engine, near cylinder 1, from the valley side. Can't really detect the noise from the valve cover area or the injector side of that cylinder.

Could it be a collapsed lifter? How do you determine if you have a collapsed lifter? Wouldn't that also make the engine run rough because that valve wouldn't be opening all the way?

The noise doesn't seem to affect the running of the engine at all. It's just an annoying knocking sound that I know should not be there.

Any other suggestions would be welcome.

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Old 02-04-2005, 02:09 PM
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Is the knocking sound consistant every revolution?

I know that my 86 6.2 had a noise to it, it sounded slightly like a knock, it was faint, sometimes worse. Not a metallic noise either. Here not too long ago I pulled it all apart (a write up coming this weekend with pics). Well not all of it, I pulled the valve covers had a look see, nothing out of the ordinary. This was done while I was swapping out A LOT of parts, new injection pump, installed timing gears, new water pump, new rear main seal, stud girdle (I'm sure I missed something). Anyways, after I got this thing back together, no noise, no nothing just a consistant sounding engine. Whew!

Here is what I think it was:

either an improperly sealed injector or the timing chain and or injection pump was that worn. The reason for the bad sealing injector, is that I recently pulled the injectors out to have them pop tested (they were rebuilds). I re-installed them the old washers on them (did this in front of the diesel shop that tested the injectors). Anyways, it ran different after doing that (this is before all the tear down and stuff). So every time you remove an injector and re-torque it, replace the copper washer!

For further diagnosis, pull the valve covers, look at the rockers. and how far down the push rods go while everything is together. IF you see a pushrod or rocker sitting unsually lower that the rest you could have a collapsed lifter. Some pics of a collapsed lifter(s) can be seen in the "ebay find" post here in the 6.2 forum. Also you can push down on the rockers (push rod side) it goes down with you pushing on it, you have a lifter thats not holding pressure, its bad.
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Old 02-04-2005, 03:09 PM
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Thumbs up

Thanks, John.

The noise seems to be every cam revolution, not crank. That could mean something in the valve train, or perhaps a piston/wrist pin problem on compression stroke. Loosening the injector lines on all 8 injectors did not make the knock go away, so I'm fairly certain it's not an injector.

I have a set of DSG timing gears sitting here waiting to be installed. Both my valve covers are starting to leak oil as well. Might as well tear it all down at once, and hopefully I can find the culprit.

The sound reminds me of a knock I had on another 6.2L. It turned out to be a burr on the injection pump drive gear. However, the gear was damaged when the camshaft key sheared off due to a loose cam bolt. After filing the teeth on the drive gear, the noise went away. I don't think that's my problem now, but perhaps my timing chain is getting so worn out, it's clanking around in there? Or maybe something else being damaged by the loose timing chain?

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Old 02-04-2005, 05:24 PM
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The noises I had were not consistant with every stroke, but rather every other or intermittant, so I choke that up to be a fuel knock. I did the same thing, removing the valve covers, to fix a leak and give me peace of mind considering the sound. The 6.2 makes lots of weird noises, the colder it gets the more noises they make.

I don't think that a timing chain will get soo loose to slap around and hit the timing cover. You have about 100+K on that rebuild right with a new chain at that time?
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Old 02-05-2005, 09:33 AM
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Originally posted by john8662:

I don't think that a timing chain will get so loose to slap around and hit the timing cover. You have about 100+K on that rebuild right with a new chain at that time?
Yep, around 120K miles since I rebuilt the engine in 1995. I installed new chain and gears then.

Sheesh, I can't believe it's been ten years since I rebuilt this engine! This engine was originally built to replace a blown 5.7L diesel that I had installed into a 77 Blazer. That engine blew up on me after a trip to an RV training school in February 1995. Shortly after that, I purchased this particular 6.2L from a junkyard, and then rebuilt it. Didn't need much. It's still got the original bore, pistons, rods, crank, etc. Basically just new rings and bearings. The orignal bearings even looked fine. No telling how many miles were on it then. I think the reason the engine was junked was because the outer starter bolt ear was broken off. I didn't notice this until partway through the rebuild. The machine shop was able to fix that for me, though.

After running the 6.2L in the Blazer for about a year, I pulled it out and replaced the tired 305 in my '81 with it. Been driving that truck ever since. Except for the routine stuff like alternator belts, a couple of broken accessory mounts, two leaky injectors, and motor mounts, I haven't had to do any repairs to the engine itself. Still running the original injection pump that was on the engine. I had it rebuilt and installed rebuilt injectors. Again, all this stuff is 10 years old with 120K miles.

I'm going to replace the water pump since I'm going to be in there anyway. Doesn't show any signs of needing to be replaced, though.

Ahh....a nice trip down memory lane! [img]tongue.gif[/img]

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Old 02-05-2005, 07:28 PM
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I let my dad listen to my truck tonight. He's been playing around with diesels for years (that's what got me started), but he wasn't able to even hear the knock at first. I had to get him to stand back away from the truck at an angle in order for him to be able to hear the noise. So it's obviously not a very loud knocking, but enough of one that I'm able to determine that's it not supposed to be there. He said it sounded like a normal 6.2L to him. But of course, I've been driving this truck a long time, and I know each and every little sound it makes, and what is and isn't supposed to be there. [img]tongue.gif[/img]

On a side note, I was wrong about this rebuild being 10 years old. It was actually February of 1996 when I started on the 6.2L project. So it's only been 9 years. I guess memory is one of the first things to go! I'll be 29 in a couple of months....starting to get some gray hairs already!! Still, it's been 9 years and I haven't had to do any major repairs to the 6.2L yet!

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Old 02-05-2005, 07:54 PM
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Shortly after rebuilding my 6.5 I noticed a similar knocking noise. Sometimes it is more pronounced than others, but no one else can hear it I guess, they say it sounds fine to them. I decided that it had to be an injector or a lifter/valve train problem because all internals are new... Sorry I can't be more help, but thought you might like to know that you aren't alone.
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Old 01-23-2007, 10:16 PM
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DmaxMaverick DmaxMaverick is offline
Join Date: Apr 2001
Location: CA
Posts: 11,881

TTT for Arveetek
1985 Blazer 6.2
2001 GMC 2500HD D/A
2014 Chevy Cruze Diesel - Fabulous car, no problems at all, but sold Nov. 2016 @ 55K miles.
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Old 01-24-2007, 07:39 PM
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belizean6.2 belizean6.2 is offline
Join Date: Jan 2007
Location: Belize
Posts: 9

I also have a knocking noise from my 6.2. This engine hase been rebuilt, and before it used to knock like crazy. But now it only knocks when i start it in the morning. My mechanic says that it could be fuel draining back into the tank when sitting over night. i dont get hard starts just a loud knock after it warms up is runns like a champ. I will take it to be tuned soon so i will let you guys know what happened.

i think any stange knock coming from a 6.2 should be taken seriously. I learned the hard way that this is the sound of something no so good that is going to happen...
1991 Chevy Silverado 2WD Fabtech 4" lift
6.2 Diesel
Fresh Overhaul
Reman injectors
Reman IP
Soon to be turboed!!!
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