Have a '93 chevy 1500 wt with a vortec v6 - 4.3L, over 200,000 miles. The problem isknocking. The knockingis always present when the vehicle is running, but builds as the engine temperatureincreases.

So, when i first start the truck, the knock is not very noticeable. It then begins to get louder. The knock is not as detectable at highway speed (50+). It is the worst when the car is in drive, but stopped - at a stoplight for example. If I put the vehicle into Neutral, the knock subsides, but is still present.

You can feel the knock through the gear select handle - the vibrations are coming through the steering column. When you look behind the harmonic balancer, where the "shaft" for the balancer goes into the bottom of the block, you can see a slight "jump" that coincides with the knocking. So what i see is movement of that "shaft" that matches the timing of the knocking. The seal at that juncture is still present, but i believe it is the source of the oil left on the ground whereever the truck is parked.

I've had a few people listen to it. One thought is the cam is broken, causing the "jumping." I think this could be possible if the break wasnt perpendicular to the cam's length, rather at a diagonal along the length. in my mind this would allow the cam to maintainitsrotation withthe overlapping sections.

basically i'm looking for possible causes of this knocking. i would like to fix it but not at great expense. some have mentioned crated motors. an option but not cheap.

 

This sounds like a possible cracked flexplate (flywheel) Is the bell housing loose or has it been?
I can't see the crankshaft moving back and forth unless the thrust bearing or washer part of the crank is worn out. If it is this could be your noise too and you would have to try a pry bar to move the crank to tell for sure.
A broken cam is next thing to impossible and still be able to run.

 

thanks for the thoughts, especiallyrelated to possible broken cam. will do more investigating and see what i can find.