A few weeks ago a knocking started in my 1988 L98. It was first thought to be a rod, then a main from a fellow wrench turner. Then, another friend ( with more time turning wrenches on a C4) indicated that when the noise was present, it sounded to him like a lifter. Reason was, the sound comes and goes, it not present all the time and is not the same volume. So, off comes the intake and now some $900 later with new roller lifters, new pushrods, new roller rockers and some other upgrades the sound is still there. He swears the sound is on the upper part of the engine, and is not down inside, or "deep" enough sound for a rod or main. Now, we are looking at replacing the heads with new ones. Problem is, I'm not ready for another $1500-$2000 on a head replacement.

Can anyone think of any reason for a knocking sound that comes and goes? Oil press is fine, enigne runs fine, and then knocks. It seems that at times with the knock appears there is a dead miss now and then that tends to come and go with the sound. ( perhaps indicating a valve?).

I just had the Keisler tremec trans kit installed recently. At times jsut after the installation I would smell clutch... Now, I am not saying the two issues are in the least related, but I did not have any issues with the engine and this sound before the trans swap... any ideas?

Any ideas would be appreciated..... Dan

 

Rod bearing knocks don't come and go, they are continuous until failure.
If it does it while idling, you need to get a stethascope and listen for where the noise is coming from. A loose clutch bolt can strike the dust cover or bell housing causing the intermittent knock. You can pull the oil pan and measure bearing clearance on rods and mains with wax gauges and prove the bearings are or are not the problem.

 

Pulled the left head, number 5 piston had been beat to hell. Small metal object located in exhaust pipe just before the converter. Seems the small metal object did the damage and passed on. What is was, or where it came from is a total mystery. No indications of any object coming in via the mass air ( screen intact), nothing missing from the intake or other pathways that we can think of.
Sort of like trying to figure out the Kennedy assasination.. now at least we have the magic bullet in hand, just cannot find out where it came from. Fix is to replace or rebuild heads, and pull number 5 piston for inspection for possible replacement.
Darnest thing have ever seen to date!

 

Can we see a pic of the damaged piston and the offending "piece"? This may help one of us to identify the "piece".

Aaron