I know, I know... I shouldn't be on the Z28 board discussing a 350-powered Chevy Astro, but I need some help here. I have a 1973 350 that has some sort of knock ONLY at idle and ONLY when the motor is warmed up. When I take the serpentine belt off, it seems to quiet down a lot, so I have replaced EVERY front accessory except for the clutch fan. Using a stethoscope, I can hear this knock through my alternator case and some through the right valve cover. I've re-adjusted all the valves. It seems to be on the right side somewhere. It's a slow steady deep knock that sounds like when you hit your knuckle on your computer desk.

Check out this link to see the whole story:
http://www.astrosafari.net/cgi-bin/i...t=ST;f=14;t=58
My screen name over there is "Lotsokids."

Thanks for your help.

 

you have an internal knock, it could be a broken piston, wiped out bearing or a bad wrist pin. It happens when it warms up b/c your clearances increase w/ temp. You wasted your money on new accesories, the knock quiets w/ the belt off b/c there is less load on an engine turning no accesories. good luck

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95' T/a m6
383-ported Lt-1's
Scat crank, eagle rods, custom Fed-Mogul pistons
headers, car back, etc
Ed Wright tuning
to much other stuff
9-inch rear on the way

Owner of
Tischler Competiton Engines-Somerville N.J.

 

I removed the engine yesterday and opened it up today. I found that there was a bad spot on the crank and wiped out #1 rod bearing. I'm putting it back together now with a new crank and bearings.

Thanks for the info.

 

did you have the rod resized?
Hate to tell you, but once you have the bearing go, the rod big end is free to knock around on the crank journal (and hence the sound)
Thing is, all this banging around will usually elongate the rod big end. Now that the rod is out of round, the bearing clearances will be off, allowing the oil film to break down, and the problem can come right back again...

 

No, I didn't resize the rods. I just plastigaged them all and hoping for the best. I just got it running again tonight. Good oil pressure, no knocking, no leaks... RUNS GREAT!!!

Anyone wanna race a Chevy Astro?