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Discussion Starter · #1 ·
I own a 1974 chevy sbc 350 and a couple months ago my brother drove my truck home from work and said when he went to start it, a bunch of black smoke came out of the exhaust pipes and i could hear the knocking when he pulled up. knocking both in gear and at idle. He shut it off and started it again and there it was, thick black smoke came out of the exhaust. The knocking sounded towards the transmission side of the engine but i couldn't tell for sure. My dad said maybe bent piston rods. I did compression tests on all 8 cylinders and there's only minor deviations, nothing out of the ordinary. Anyone have any idea what it is? I keep reading stuck fuel injectors but i do not have fuel injectors. also issues valve lashes but i dont know. TIA
 

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Black smoke is generally fuel related. Oil being white or bluish tinted. Water tends to be white and evaporates quickly.
 

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Discussion Starter · #5 ·
Take the valve covers off and see if any of the rockers are loose and if they are overly tight. You can back them off a 1/4 turn or so and see if they loosen up. You will need to roll the motor over to the right spot for each cylinder.

But i would do a leak down test first. You can borrow a tester at most auto parts stores. This help find out if the valves are leaking or rings bad.

Fuel injected motor would knock and smoke with stuck injector. But so could a carb with a malfunction that was flooding the motor like stuck floats. Pull the dipstick and oil cap and see if you can smell gas inside the motor or on the dipstick. An oil change may also show up some of the problems. Metal flakes water or gas in the oil will be pretty easy to see. Cut the oil filter If you have a magnetic drain plug you can see if its grabbed anything.

Hope this helps.
yeah ill definitly try that. thanks for the advice
 

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I own a 1974 chevy sbc 350 and a couple months ago my brother drove my truck home from work and said when he went to start it, a bunch of black smoke came out of the exhaust pipes and i could hear the knocking when he pulled up. knocking both in gear and at idle. He shut it off and started it again and there it was, thick black smoke came out of the exhaust. The knocking sounded towards the transmission side of the engine but i couldn't tell for sure. My dad said maybe bent piston rods. I did compression tests on all 8 cylinders and there's only minor deviations, nothing out of the ordinary. Anyone have any idea what it is? I keep reading stuck fuel injectors but i do not have fuel injectors. also issues valve lashes but i dont know. TIA

First place I'd go is the cam has digested a lobe and lifter or more than 1. This is right in the era for that event. Another high on my probability list would be the timing set is worn out and has let the cam fall out of synch with the crankshaft.


A compression test often doesn't indicate either of these conditions. For the failed lobe and lifter pull the rocker covers and observe the rocker motion with the engine running, looking for an obvious lack of lift at the valves.


For the timing set wearing out an early indicator is a frequent need to readjust the distributor timing to advance it. A running test with a timing light can be done by running the RPMs up then closing the throttle quickly while using the light to see if the timing wanders back a forth more than a couple, three degrees.


Bogie
 

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Discussion Starter · #7 ·
First place I'd go is the cam has digested a lobe and lifter or more than 1. This is right in the era for that event. Another high on my probability list would be the timing set is worn out and has let the cam fall out of synch with the crankshaft.


A compression test often doesn't indicate either of these conditions. For the failed lobe and lifter pull the rocker covers and observe the rocker motion with the engine running, looking for an obvious lack of lift at the valves.


For the timing set wearing out an early indicator is a frequent need to readjust the distributor timing to advance it. A running test with a timing light can be done by running the RPMs up then closing the throttle quickly while using the light to see if the timing wanders back a forth more than a couple, three degrees.


Bogie
will do boss, thanks
 

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JMHO, black smoke is too much fuel. Check your carb or injectors as hcompton suggested. Too much fuel will cause lots of black smoke and pre-ignition with excessive unburned fuel going into the exhaust igniting in the headers, making the motor knock.
 
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