backyardsinger

76 l48 350 automatic with air knocking from front of engine at idle the ac does not work so belt has been removed new water pump and alternator and belts I used a rubber hose and thought it was the timing chain after I removed the belts I started the car I do not hear a knock I put just the power steering belt back on and have a little knock maybe 1\4 of the original pulled the belt back off yanked on the crank pully nothing feels loose I could use some feedback where to go next I drive this car 2-3 times a week since I bought it in may and keep fixing what goes bad it sat for quite a while

SH-60B

None of the acccesories are loose or hitting something adjacent? Is the harmonic balancer in good shape? The inertia ring can disbond from the hub and make noise.

Richard454

Have you tried pulling one plug wire at a time?


Richard

CanadaGrant

You said you removed all the belts and it went away. Since you have checked the damper look for movement from the water pump pulley/shaft. Also if you replaced the belts, try it with the old ones and see how that works.

pauldana

Can you make a video with audio so we can hear it?
That may help us help you:-)

toobroketoretire

Maybe the three 3/8" bolts that hold the pulleys on are loose.

gjohnson

Smog pump? They can make a knocking type noise if bad.

backyardsinger

The bolt for the harmonic balancer was just loose enough that I could spin the washer with my finger I have no idea why it would loosen up but I plan on doing the timing chain with a new cover and gaskets when I up grade to an aluminium radiator and electric fans I will replace the balancer at that time until then thank you for the help tops off and throttle down.

CanadaGrant

Hopefully the crank snout keyway isn't damaged from the loose balancer. Glad you found it.

toobroketoretire

The old 265", 283", and 327" crank snouts weren't drilled and tapped; their dampers were driven on with (you guessed it) with a BIG hammer.

SH-60B

The OP has a 350"

BOOT77

Check the fuel pump, I went thru 2 stock replacements. 1st blew the diaphragm and last one still worked good but always knocked. Use a stethoscope, piece of pipe or long rod and put it on the pump. Aftermarket pumps have a spring to keep it from happening, but no return so you gotta be creative. Could also be just wear on the pump pushrod.

sierra 43

Just for what it is worth. My 80 C3 with an L48 had a knocking noise at idle also. As soon as you gave it gas the knock went away. The smog pump and ac have been removed, it has an Edelbrock carb and performer intake, true dual exhausts. After spending weeks chasing it we found the flex plate was cracked. Replaced it and knock is gone. Good luck with your car. (Now time to fix the C4's Optispark, arghh!).

pauldana

Crank snout bolt.... Bummer... I had this also happen to me once.... The snout bent slightly because of this... Then eventually broke:-(

Good luck

toobroketoretire

Yes, I'm well aware of what he has. I was just pointing out the previous V8's had their dampers driven on with no bolt/washer to hold them on.

SH-60B

[QUOTE=toobroketoretire;1591008286]Yes, I'm well aware of what he has. I was just pointing out the previous V8's had their dampers driven on with no bolt/washer to hold them on.[/Q


All of no use to the OP.