Help! Small block 360 has a knocking sound

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How are the water pump and alternator bearing/bushings? Any slop. What does it do when you put it in gear?

On your compression test, was that cold, hot and did you add oil in the cylinder before testing it? Why do you think it had carbon build up?
 
How fresh is the engine? Is it still close to its break in? It sounds to me like diesel knock. That's indicative of high cylinder pressure. Piston slap. Engines with really high cylinder pressure like that one has, will usually exhibit a diesel like knock mostly when cold, but it gets a little quieter as the engine warms. Usually, it's most audible JUST above idle, with the throttle barely cracked. If that's what it turns out to be, ride on brother. It's normal.


The engine was rebuilt prolly about 15-17 years ago, nowhere near fresh. However, I am the only person person to actually put some miles on the thing. I have only been driving it for about two years, and the engine has never made this sound until now.
 
The engine was rebuilt prolly about 15-17 years ago, nowhere near fresh. However, I am the only person person to actually put some miles on the thing. I have only been driving it for about two years, and the engine has never made this sound until now.

Help an old guy out here. My hearing is terrible, plus your audio is too......no offense. lol Is it ONE knock or several? If it's several, it could be exactly what I am referring to.
 
ok, what do you suggest I look for? I have pulled the valve covers and watched it run, and everything is oiled and working just fine. No bent push rods, nothing was loose, all valves are opening and closing just fine.
Those are all things I would have looked for
Stock rockers?
Hydraulic lifters?
No signs of excessive wear on the rocker shafts?
 
How are the water pump and alternator bearing/bushings? Any slop. What does it do when you put it in gear?

On your compression test, was that cold, hot and did you add oil in the cylinder before testing it? Why do you think it had carbon build up?


The water pump and alternator bearings are ok, no slop. When it goes in gear the knock gets slightly quieter at idle, otherwise it stays exactly the same.

As for the compression test, it was hot, and I did not add oil to the cylinder before testing it. The reason for the carbon build up is for multiple reasons. First of all the car wasn't put together by me, it was put together by some Tennessee rednecks, I'm just the lucky one who wound up with it. They put a big cam in it, but it has 2.45:1 gears in the rear end. Plus, it always runs rich, I can't seem to get it to quit running rich. My theory is, the engine never got to any decent rpm's while driving, and with it running rich, its just got carboned up. Every time I pull the spark plugs out, they are solid black. They are dry though, so no oil issues.
 
Help an old guy out here. My hearing is terrible, plus your audio is too......no offense. lol Is it ONE knock or several? If it's several, it could be exactly what I am referring to.

To me it sounds like a single very distinct knock, only towards the back of the engine.
 
Not a rod or a piston, those have very distinct knocks. A stethoscope will help narrow it down. If you suspect an exhaust leak, then listening through a length of heater hose will help narrow down where the noise is coming from.
 
How are the water pump and alternator bearing/bushings? Any slop. What does it do when you put it in gear?

On your compression test, was that cold, hot and did you add oil in the cylinder before testing it? Why do you think it had carbon build up?
I like the question about what does it sound like when you put it in gear. If it gets louder that can indicate an exhaust leak. Do you have any issues with backfiring at all?
I have another question, at what rpm is the engine idling in the video? Because it seems kinda fast to me. What is your manifold vacuum at idle and rpm?
 
I had a similar knock on this 69 340 in the 80's. It knocked at idle and leaving off. But seam to get quieter when under a pull. I drove it hard back and forth to work for about 2 years. I finally pulled the motor and found the piston pin was loose and hammering up and down. no wall damage at all clips were still in place

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Pull the plug wires off one at a time while it's idling. see if the knock goes away (I don't think it will). If it does, then it's wrist pin/rod related. I doubt it will go away. We are all throwing out guesses off of bad audio. time to start trying things.... lol
 
I like the question about what does it sound like when you put it in gear. If it gets louder that can indicate an exhaust leak. Do you have any issues with backfiring at all?
I have another question, at what rpm is the engine idling in the video? Because it seems kinda fast to me. What is your manifold vacuum at idle and rpm?


Nope, no backfiring issues at all. I believe it was idling a bit high, but I don't remember what the tach said. I believe the vacuum at idle was around 20 Inches last time I checked it.
 
Help an old guy out here. My hearing is terrible, plus your audio is too......no offense. lol Is it ONE knock or several? If it's several, it could be exactly what I am referring to.


LOL. I'm in the same boat as you. Even with no other sounds in the background, I can ever hear these video downloads worth a crap. Even if I put my ear buds in, I just can't quite get comfortable saying what I'm hearing.

I usually don't even listen to them. But I did this one and I got nothing. If I was standing there...that would be different. But I can't even venture a decent guess. I will say that the others in this thread have given the OP the proper stuff to check.

The flex plate. Had a buddy that installed a new converter and it developed a knock about 50 miles after the change. Sounded like a Rod, but I told him beforehand to only use RED locktite on the bolts that hold the converter to the flex plate. Of course he didn't, and he had the pan off long before he even checked those bolts. And that's what his issue was.

So the flex plate to crank bolts, flex plate to converter bolts, flex plate cracks or broken pump drive on the converter are all good places to start.

I've heard fuel pumps knock too. I've seen the eccentric come loose and sound like a bottom end issue. Another bolt that demands locktite.

Could be a collapsed piston skirt, or as OMM said, a jacked up wrist pin.

Sounds travel. The OP just needs to pick a spot and start looking stuff over. And getting a stick or similar and using that to maybe help narrow down where the noise is originating from.

Wow...that's bad grammar. But it's early...
 
Its kinda hard to tell because the knock is so loud, but it seems more towards the top of the engine.
take a long handled screw driver, carefully with the engine running, set the tip of the screwdriver on the valve cover and then put your ear to the handle. you'll hear the sound if its in there or not. Just watch out for moving belts and electrical wires
 
As others have suggested, check your torque converter to flex plate bolts. If only one backed out just a little it will make noises like you are hearing. I was stubborn and didn't check mine right away because I was "sure" I had put loctite on those bolts. Evidently I did not because that is exactly what it was. Won't take you very long to check. Check for exhaust leak too.
 
My first thought was flex plate bolt. Its too fast of rhythm for valvetrain . Not loud enough for rod knock.
 
200 psi is way too high for pump fuel, and no way 'carbon build up' will push it up that high. Try another compression gauge first. And an actual 9:1 compression ratio and moderate to big cam won't end up close to 200 psi cranking pressure... maybe 145 psi. So I really suspect your gauge is off, and if so, it may be masking some cylinder pressure variations. You said 'most' of the cylinders ware at 200?

The only other way to get such high cranking pressures is the timing is waaaaay advanced. That would have to have happened during assembly. If the engine has been running OK, then that is not logical (and things won't fail more advanced).

The exhaust note when you went around back is sputtering and fluttering, like the exhaust valves are not closing properly all the time, or some cylinders are misfiring. So if the cylinders' compression are OK (which is still unknown based on those not-logical compression readings IMHO), that points to valve leaks or intake leaks or cam/valve problems. The sound at the end has a distinct miss going up with RPM's so 1-2 cylinders are not firing right at all.

So was this running OK before?
 
200 psi is way too high for pump fuel, and no way 'carbon build up' will push it up that high. Try another compression gauge first. And an actual 9:1 compression ratio and moderate to big cam won't end up close to 200 psi cranking pressure... maybe 145 psi. So I really suspect your gauge is off, and if so, it may be masking some cylinder pressure variations. You said 'most' of the cylinders ware at 200?

The only other way to get such high cranking pressures is the timing is waaaaay advanced. That would have to have happened during assembly. If the engine has been running OK, then that is not logical (and things won't fail more advanced).

The exhaust note when you went around back is sputtering and fluttering, like the exhaust valves are not closing properly all the time, or some cylinders are misfiring. So if the cylinders' compression are OK (which is still unknown based on those not-logical compression readings IMHO), that points to valve leaks or intake leaks or cam/valve problems. The sound at the end has a distinct miss going up with RPM's so 1-2 cylinders are not firing right at all.

So was this running OK before?
Timing chain jump a tooth or two?
 
I want to say a magnum engine was around 180 psi of compression stock. Many current engines run 200 psi or more. Small block chevy vortec seen them at 205 psi stock.
 
Timing chain jump a tooth or two?
Sure might make it run like this.
That would retard the cam if it happened while running and give lower compression numbers.... (But I don't think those numbers are right anyway unless the OP has some biiiig pop-up pistons in there.)
 
Many current engines run 200 psi or more. Small block chevy vortec seen them at 205 psi stock.
Yes but the newer engines are running very different roller cam profiles and some darned high compression ratios, with good spark control to stay out of detonation. A very different animal. Trust me: No 9:1 LA with flat lifter cam is gonna run 200 psi numbers..... unless the cam is way too small and the SCR is up past 11 or 12:1.... or the lifters and/or cam lobes are all screwed up and not lifting the valves like they should.

BTW, a couple of bent pushrods could make this run this way.
 
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Yes but the newer engines are running very different roller cam profiles and some darned high compression ratios, with good spark control to stay out of detonation. A very different animal. Trust me: No 9:1 LA with flat lifter cam is gonna run 200 psi numbers..... unless the cam is way too small and the SCR is up past 11 or 12:1.... or the lifters and/or cam lobes are all screwed up and not lifting the valves like they should.

BTW, a couple of bent pushrods could make this run this way.
Or a wiped/flattened cam lobe(s)?
 
There are only two things I have ever heard make that sound;
1) is a wrist pin, and
2) was a flatted lobe,
But the the lobe was a whole bunch quieter, and was of a slower cadence..

I've never heard of anyone getting away with 200psi, with iron heads ,on the street,which is all I know.

Isolate the cylinder by removing the plug wires one atta time. When you find it, check for rocker arm play with the piston parked at TDC compression. If none then suck the piston down the bore a half inch or so be hand-rotating the crank. Then insert a metal rod thru the plug hole with one end resting near the center of the piston.Then attempt to push the piston down. If the wristpin is loose the piston will drop down a few thou,easily, then stop. Back the crank up a few degrees and repeat to verify.It will be obvious.
 
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