hi i have a 67 chevelle and it is producing a knock at idle only when the engine's warm usually around 200 degrees. there is no knock before it gets that warm. i have tried messing with the timing at idle 10,12,14 degrees and it didn't go away. I've also tried adjusting the idle mixture screws and no change there either i am running 91 octane fuel as well i was thinking of adding an octane booster to see if fuel was still the problem. any suggestions would be great

thanks
tim

I'd check for a knocking lifter or rod/main bearing. Try to locate the sound, if its from the bottom or the top of the engine.
Good luck
Matt

Sometimes a collapsed lifter or spun bearing will not create a knock until the oil flowing thru it has warmed and "thinned". You can take a dowel and press it on different areas of the block while holding the end to your ear while the engine idles. This acts as a stethescope and may allow you to pinpoint the source of the knock.

Be extremely careful and use your fist at the end of the dowel to protect your head (common sense)

thanks i'll give that a try and see if i can locate the source of the knock.