I just took the egine out of my camaro and put it in my truck (81 GMC 1/2 ton), and now the engine sounds like it's knocking. It's only at idle, though. Once it gets past about 800 - 900 rpm, the engine smooths out, and the knock goes away. I only have open headers right now, so I'm hoping it's one of those "men in black" explanations. You know, the exhaust echoing of the rear end and refracted by the planet Venus or something. Anyways, what could be causing this? I used a length of fuel line to try and isolate the sound, but I couldn't find it. I thought it could be a bad lifter/munched cam lobe and it only pumps up at 800 rpm and quiets out. It didn't make this sound in the camaro. I've only got about 10 miles of street driving on it, but it has idled quite a bit. Oil pressure is also good (20psi at a 450 idle and 180*). It has that hollow sound like a rod, but like I said, I can't isolate the sound with tubing. One thing that may be relivent, My bro in law helped me break it in, and we didn't exactly follow the recommended cam break in proceedure. We idled it for 10 minutes and cut it off. Then I did the break in the next day.

I'm going to get exhaust put on at the end of the week, and I hope it'll go away. I have to get the trans put in first. That'll hopefully happen in the morning.

 

Berl,

The interruption in the cam break-in procedure PROBABLY shouldn't have caused any problems - probably. You really should have run the engine at higher RPM for proper cam break-in and lobe polishing. You might want to remove the intake and get a good look at the cam lobes just to be sure. If a lobe or two are galled and not polished, you may be shopping for a new cam and lifters.

And since you wer only idling and then shut it off overnight, it is possible the the oil pump got a massive slurp of moly particles when you restarted and a good quantity of them packed into a bearing somewhere. However, I would presume that after prolonged operation the oil would have flushed that out before there was any real damage. That's just all speculation, though.

The pressure seems to be O.K. at the speed and temperature. Does the pressure rise with RPM?

 

Yes, it rises to 60 psi at around 2000 - 2500 rpm. Maybe sooner, I'm not sure. The noise goes away at about 800 rpm at the same time the engine looses it's lope from the idle. I have a 270* cam, so it has a decent lope at idle. After the interuption the first time I started it, I ran the cam in at the recommended rpm and time. I had it in the camaro for a few months, but didn't drive it much because of transmission problems, but it ran strong and didn't make that noise. I did run it for a short time in the camaro with open shorties, but I doubt I could have heard it if a rod came thru the block like that. At any rate, this is a new sound.

One other thing that may be related: there doesn't seem to be much oil coming thru the rockers. At the initial start up, it took a very tense 40 seconds for oil to come thru the rockers. Now it just doesn't have the volume I expected. It doesn't squirt out, just a decent looking flow. That doesn't worry me that much, though. Because the oil starts right after the engine cranks, now. I'm running Comp Cams Magnum roller tip rockers if that makes any difference.

 

Ok, I got the exhaust on, and the noise moved to the back of the truck at the tailpipes. I'm guessing it's nothing to worry about. I can hear the valves ticking now, though. Thanks for the help, Vader.