Originally Posted by rattychevy
I just bought my forth c10, 1977 with 350, th350. The engine is bone stock 4bbl quadrajet, adjusted the valves, just did plugs, wires, cap, rotor, new vacuum advance(old one leaked), new mechanical advance springs, one heavy one light, adjusted the carve and got timing where I think it needs to be, no timing light yet. It fires up on a dime, pulls pretty good. My problem is when in gear, giving very light throttle I have a "knock". Above 1200-1500 its gone. And at idle its not there. I can't figure out what it is. Any help would be appreciated.
What kind of knock?
- Detonation/preignition usually makes a rapid series of knocks that goes away when the throttle is closed. It's unusual in low gear because the engine has a tremendous mechanical advantage against the load it has to move, not unknown just unusual.
- Single heavy knock can be a main bearing with excessive clearance. This tends to soften if not go away with a closed throttle.
- A double heavy knock is an indication that a rod bearing has failed or is clearanced excessively.
- Similar to rod bearing knocks in cadence if not tone is pin and piston skirt noises.
- Valve train tends to be more of a tick or clatter.
- Up front the water pump or alternator bearings can make a moderately loud and heavy sound perhaps more of a growl or grinding sound.
- Flywheel and clutch sounds are pretty variable from loose bolts, the pilot bearing worn out, the shaft splines worn or damaged, the throw out bearing shot, the tranny input shaft bearing worn out. These tend to be single sounds that vary in tone, easy to pick out from engine noise with a stethoscope.