Did you ever check the converter bolts? If they are all tight then id look into a lifter losing prime.

Also was your transmission rebuilt or did you buy another transmission and swap your bellhousing over?

Also id slap a 5.3 or 6.0 in it for less than building the motor to be anything more than a fresh rebuild.

 

Super- My 2001 chevy HD 2500 6.0 work truck is doing the same thing. The noise which sounds like valvetrain comes and goes. It doesn't happen everyday. I can start my truck up in the morning and it will be fine then I jump on the freeway and a couple miles down the freeway it will start clacking really loud then go away. Then it won't happen for a few days or even a week or 2 . Then out of the blue it will do it again and for longer periods of time then go away. My truck has 295,000 miles on the original motor so I expect it to make some noise but I don't know if I should change the cam/lifters or just put a new engine in it. BTW the engine is still very strong with no issues other that the loud clacking.

 

I would check the converter bolts as well.

As a new idea my truck sounded like this when the fuel pump was on its way out. It would make this sound at random. Almost consistant when it was cold after driving it a few miles. Used to scare the hell out of me.

LeanFuelKnock.mp4



When this noise is happening what does your oil pressure look like???

 

The converter bolts are fine. I had my trans rebuilt. It was making the noise before the trans swap just has gotten worse. My engine has about 110k on it and also is running great other than this terrible noise. I have checked the fuel pressure and it is right where it is supposed to me. This may sound dumb but I don't have a working oil pressure gauge. Im planning to buy all autometers and the whole set is going to cost me about 800 bux. The trans going out used up all of my cash for things like this so for right now I only have the stock truck gauges hooked up. So basically I have all I need except a working oil pressure and speedometer. I have got to get my funds back up. Just purchased a new house and the down payment on that with the added cost of the trans and other things that wern't expected in the build and im broke. I do hope this is something as simple as a lifter but it sure does sound loud and heavy. Just don't understand why it would be quite sometimes if it is something in the bottom end. Thanks for all the input and help guys!

 

Im worried it is a rod. Is there any way to check the lifters without removing the heads?

 

After a lot of thing I believe I have figured out the problem guys........................................I think it's going through metamorphisis just like a butterfly except its turning from a gasoline engine to a diesel

 

You didn't seriously put diesel in it did you? Lol.

It still sounds like a dying lifter.

 

haha no I didn't put diesel in it. Is there no way to be sure about the lifters without pulling the heads?

 

The only way I have done this is to pull the heads to check the lifters.

 

Do you guys think it would be worth it to dump some seafoam in the engine and drive it say 500miles or so before changing it and see if it helps any? Lucas maybe?