motor knock at idle

[mr jims boat]

Im restoring a 67 starcraft with the 153 cdi 120 hp motor the inside of the motor looks new but sat up since 2007 i just had it to the water yesterday and started it up it started great left it fast idle at 850 rpm warmed it up and dropped it back to normal idle 500 and a knock started? sat it back to high idle went away. doesnt do it in gear and i ran it a few yards from shore and have plenty of power very responsive. soHELP!!!!!

 

[alldodge]

:welcome: to iboats

Is this a knock or a loud tic or tap?
What was your oil pressure reading when it knocks/tic?