hey guys i just rebuilt my 98 3.8L engine about a month and a half ago and ever since i started driving the car i've been hearing a soft knocking sound. it sounds more profound when the engine cools off and then i start it up again. im thinking it might be a valve issue or maybe an oil issue, im using 5w30 oil right now. any suggestions? thanks

 

are the valves tightened to the right torque amount ? are you using the correct octane ? is it the valves or the lifter making noise ?

 

A valve tappet will make a ticking sort of sound. Sound from a valve would be centralized to the upper area of the engine. A rod or piston makes a more solid hollow sounding knock and will sound like it is coming from the lower part of the engine. Since yours seems to go away when hot, it may be piston slap (wrist pin loose in the piston).

 

i assume the valves are tightened to the right torque because it was rebuilt at an engine shop. the lifters are brand new so i doubt its that. im not sure if it might have to do with the octane but ill change fuel and see if it makes a difference. if it is a piston slap how do i go about fixing it?

 

The only fix is new piston/rod. Take it to the shop that built it and have them listen.