Engine Knock

[Adub]

I just picked up a 79 Sierra 4x4. The engine knocks, but its a funny knock. It sounds like a rod bolt came loose and is hitting the oil pan. Has anyone ever heard of this? If that is the case, can I just drop the pan and replace the bolt?

AW

 

[big83chevy4x4]

usually if the rod broke or came loose, it would have thrown the rod. i would pull the pan to see if it is in the lower end or not.

 

[POWERMAD]

A loose timing chain will slap the cover.
From that description I would look there first.
You can pop the distributor cap off and rotate the crank back and forth and see how much the crank moves in relation to the rotor to give a rough idea on how much slop is in the chain.

 

[Adub]

Its not a broken rod. I have heard dealt with that. It sounds like a bolt hitting the pan. The engine runs well, though I have only driven it briefly. Ill check the distributor out

AW

 

[tomseviltwin]

Classic flex plate issue. Pull inspection cover and check for grooves where the tc bolts are hitting it.

 

[Adub]

Never thought about that. Previous owner said flexplate was warped causing the starter to stick occasionally. I bet thats it.

AW

 

[mudjunkie 82]

My buddys truck had the Death knock. Turned out to be a spun bearing.It would not do it all the time though, maybe every 10 Minutes once or twice

 

[Adub]

nah this does it every time

 

[87BrnRsd]

I agree with tomseviltwin. Sounds exactly like a cracked flexplate. And like stated above, check right around the bolts that hold the flexplate to the tc, usually it will crack in a circle around those holes. I know for certain that a cracked flexplate can cause a noise that is almost identical to an engine knock.
-Harrison