Hi Guys, I'm stumped on this one. Got a L98 in my 91 Trans Am GTA and it makes a clacking on start up. Runs fine cold but after it warms up it makes a clacking noise when you give it a little gas and when you lightly let off the gas. It makes no noise on full throttle, idle or when you fully let off the throttle. I thought it might be the lifters so I replaced them, then I thought well maybe the timing chain so I replaced it. Now I am thinking maybe the distributor? It doesn't sound like a rod knock or it would do it all the time right? Could be wrong though. Just thought I would run this one by the forum before I pull the engine.

Thoughts?

 

Exhaust leak?

 

Check your flywheel bolts or for a cracked flywheel. I have seen that before. Also, what is your oil pressure?

 

have you correctly adjusted your valves? I do it this way ,buy the clips that go on the rocker arms,have the engine running at idle, back off each nut slowly till you get a clacking, then tighten them slowly just till the sound goes away, then go one full turn more and your done. doesent matter where you start or stop either.what you describe sounds to me like the valve train aint quite right.

 

No, not an exhaust leak. It's more metallic.

 

Just swap in a 5 speed and it's still there. So flywheel is out. Oil pressure is at 30ish idle and 55ish while driving.

 

I would have to agree, however, I did replace the lifters and re-adjust the valves according to the book(not running) and the noise is still there. I could try the running method though.

 

The flywheel thing gave me a thought. I'm gonna look for a loose bracket or something. I'll keep you guys posted.

 

doing it with the engine running lets you adjust them in "real time" .and you get a much better end result.

 

Did changing lifters change the noise?

 

I'll give it a try. Couldn't hurt.

 

Well, turns out it is a rod knock.......That's what I figured but I was hoping. Oh well, time for a new crank...

 

no hold on a minute, if it aint knocking bad you can re use the crank AFTER you have it turned and sonic checked. but I always toss the rod on the knocking cyl.

 

Yea, I'll have the crank turned and cleaned up. The rod will get pitched...no reason to take a chance on that.