Popping noise coming from a 1972 Chevrolet C10 350?

Question

It runs, but when you're cranking it or while it's running, there is a pooping noise coming from it. My auto tech teacher swears I flattened the cam but I say it's the old timing chain because it constantly needs to be reset. What do you think?

It's probably obvious, but I meant popping instead of pooping.

Answer 1

it probably is a worn camshaft exhaust lobe on one of the cylinders. the easiest way to tell if it is the cam is to run the engine and then, with the engine running, pull each of the spark plug wires off one at a time while keeping the rpm up. As you pull the plug wire off of the plug listen to see if the popping goes away. if it does, the problem is with that cylinder. if the noise doesn't go away, try the next cylinder and the one after that on down the line. if the noise doesn't go away after shorting out each cylinder then its not the camshaft. if the noise goes away on one cylinder then you can remove the valve cover for that bank and look to see if the rocker arm is moving up and down on the exhaust valve for the affected cylinder. if the lobe is worn, it won't press down on the spring to open the valve. when that happens, the exhaust gases for that cylinder are forced back up through the carburetor because they can't get out the exhaust; hence the 'pop' as the combustion charge goes back out the way the new air is coming in.

crossed spark plug wires can cause this condition but the engine will run very rough if that is the case. a worn cam will also cause it to run rough.

a cracked distributor cap can cause a spark to arc to the adjacent cylinder and cause the misfire or pop

a worn timing chain won't cause the popping but a distributor that is set way off can (timing that is way too far advanced will cause the spark to ignite the mixture before the intake valve closes)

a restricted exhaust system such as one with a bent or smashed in pipe or a clogged muffler (very rare on the muffler) can also cause the exhaust to back up through the engine and out through the carb.

it usually is the cam but don't rule out the other possibilities

hope that helps

Answer 2

Engine is definitely worn out.The timing chain probably has more slack in it than my fishing line.As far as the poofing sound, that can be caused by the timing being out far enough to cause intake valve not in time and it is firing before the valve is totally seated.And yes, you could have a worn out cam.Another thing is that the the valves may have carbon buildup,cracks, and or just not seating enough.A wet and dry compression test will tell you how the valves and rings are doing.I myself would replace the engine.It is too old and worn out by now. A 72? Timing? Put a timing light to it and if the timing mark is 'jumping around' it is time for a new one.

Answer 3

If it's a popping noise, it's the cam. While you're replacing it, you can replace the sprockets and timing chain.

You have a flat exhaust lobe that is not opening the exhaust valve enough. There is still compression in the cylinder when the intake valve opens again, so it exhausts through the carb.

Answer 4

could be a hole in your muffler.