I have an 86 IROC, carb 305. I notice that I am getting a pretty good metalic rattley knocking sound from my drivers side when I put some quick RPM's on it while driving. It sounds like I have a rod knocking honestly. What can cause rods to start knocking only under a load? It seems most prominent at about 45-60mph when putting the throttle 1/2 way down. It just started this. It won't do it at an idle or while parked and reving it up. Thanks for any suggestions and also the solution on how to fix the problem.
Tony

 

That's typically how a knock starts...only under heavy load. To fix it right, you will need to pull the motor and rebuild it.

 

Could possibly be caused by a timing problem (lose/broke timing chain) or it could be the valves and not a rod. I would check timing first and then if thats OK move on to the internals of the engine. My engine started making noise recently too. I'm hoping its the timing chain (also have idle/stall problems) or the valves and hopefully not the rods or anything major.

 

If i get on mine under load I hear my valves chattering. Try retarding the timing. I had to go to a -5* base timing to avoid the chattering until I figure out whats wrong.

 

Detonation while under load?

 

Cool - It doesn't do it when its cold but after it is warmed up it will begin to do it.

 

That's because the oil gets thinner when it gets hot.....that's when they start knocking. Just a note, spark knock and rod knock have two very distinctive sounds.

 

Rattley knock sound?

Like hard beans in a tin can sort of sound?

Or two flat metal objects smacking each other?

there's more, but we'll "K.I.S.S"