Help! Small block 360 has a knocking sound

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I had a flexplate come loose on the crank and it sounded exactly like a rod knock untill you held it above idle then went away.
 
Its really hard to tell what the exhaust note is in the video. At least for me it is...
 
nm9stheham said:
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?
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Yes, it has always run just fine until now, as for the compression test, i used a pretty much brand new gauge, and I did everything like your supposed to. Held the throttle open while cranking and everything. I'm not sure why it has such high compression ratio, but it does. The exhaust note in the video sucks honestly, because in real life it sounds just fine, but it could still be valve train related, I am just going to have to tear it all apart and find out.
 
When I said most were at 200 PSI, that was just me being lazy. All of them are actually different readings, but all are close to about 200. The lowest reading I had was like 190, and the highest was about 205 PSI.
 
Use a stethoscope and poke around on the different engine components while it is running and see which area is the loudest of the knock.

Even check the transmission areas too while running, that sound travels through everything.

Distributor, intake, valve covers independently, timing chain cover, fuel pump, oil filter area, block, oil pan.

Infra red heat temp gun can check the exhaust temps for each cylinder at the header tubes once the engine warms up. If you have a cold cylinder that could lead you to your problem.

Especially if one of your cam lobes started going flat. Need to use the Zinc additives for the high lift hydraulic lifter cams of this era. Today's oils don't have the Zinc, and cams can go flat, especially in a higher performance setup.
 
CheeseRules01! said:
When I said most were at 200 PSI, that was just me being lazy. All of them are actually different readings, but all are close to about 200. The lowest reading I had was like 190, and the highest was about 205 PSI.
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OK, that is all OK and very consistent. BTW, having a new gauge does not mean it is a good gauge. That is why I suggest trying another gauge as a check. For you to truly have those high compression readings, you would need MUCH higher compression ratio, OR the intake valves lifting very differently than they are supposed to (like all the intake pushrods bent or all of the intake lifters collapsed or all of the intake lobes wrecked), or the cam timing advanced a couple of teeth. None of that matches well with the symptoms.

I am keying in mostly on the exhaust note, which really sounds like a couple of cylinders missing when you rev the engine a bit at the end.

One other easy thing to try: If you have a voltmeter, place it on 'ohms' and measure the resistance of each spark plug wire end to end; for standard resistance wires, they all should be between 3,000 and 10,000 ohms. Sometimes they can get hot and fail and since you had one burn out, the rest are suspect.

Did you observe anything when you looked at the plugs?
 
OK, headphone on this time before i give my opinion.
#1 it sound like its coming from the back of the motor. Flex plate bolts to tq or flex plate bolts to flywheel.
It sounds like the tin shield that cover the TQ(If its still on there) is rubbing. could be a loose bolt there that's causing the noise.
Windage tray in side motor..........Get a piece of vacuum line, 10-12 feet long. pull the dipstick tube and start sliding it into the tube. you wont need to put it in there far if the noise in in there................oh yeah, put the other end of the vacuum line in your ear:poke::D

If its not there then i'm going with carbon knock. if it is really 9.1f compression and it is truly 200 psi compression. carbon is the only answer. Us water down the carb at 2000 rpm and slowly trick it in. If your in a more farming area then i would go with ATF. Caution, it will make one hell of a Smoke screen.

Altho a flat cam is a possibility, i think it would show up as a low hole in a compression check.

This is what i would do first! if you have a shop broom, and it has a wood handle, remove it from the brush and us it as your stethoscope. or go to the lumber yard and buy you a Wood Dowel, 1/2 diameter,4-6 foot long and us that as your stethoscope.

Now probe every thing you can probe. Water pump, alt, A/C compressor. then move your way back on each valve covers and to the back of the block. The loudest noise is where you start. then go up and down, and back and forth from the loudies point.
Now it's time to get some wrenches and go to work.

My money is on the flex plate or cover.
 
nm9stheham said:
OK, that is all OK and very consistent. BTW, having a new gauge does not mean it is a good gauge. That is why I suggest trying another gauge as a check. For you to truly have those high compression readings, you would need MUCH higher compression ratio, OR the intake valves lifting very differently than they are supposed to (like all the intake pushrods bent or all of the intake lifters collapsed or all of the intake lobes wrecked), or the cam timing advanced a couple of teeth. None of that matches well with the symptoms.

I am keying in mostly on the exhaust note, which really sounds like a couple of cylinders missing when you rev the engine a bit at the end.

One other easy thing to try: If you have a voltmeter, place it on 'ohms' and measure the resistance of each spark plug wire end to end; for standard resistance wires, they all should be between 3,000 and 10,000 ohms. Sometimes they can get hot and fail and since you had one burn out, the rest are suspect.

Did you observe anything when you looked at the plugs?
Click to expand...

Once i found that i had a burnt plug wire, I replaced all 8 of them, checked the resistance on the new ones and they are all good. when I pulled the plugs the only I noticed was that they all were black, she is running a bit rich.
 
George Jets said:
Use a stethoscope and poke around on the different engine components while it is running and see which area is the loudest of the knock.

Even check the transmission areas too while running, that sound travels through everything.

Distributor, intake, valve covers independently, timing chain cover, fuel pump, oil filter area, block, oil pan.

Infra red heat temp gun can check the exhaust temps for each cylinder at the header tubes once the engine warms up. If you have a cold cylinder that could lead you to your problem.

Especially if one of your cam lobes started going flat. Need to use the Zinc additives for the high lift hydraulic lifter cams of this era. Today's oils don't have the Zinc, and cams can go flat, especially in a higher performance setup.
Click to expand...


Next time I fire it up i will go around with a stethoscope of sort and try all those things. BTW, I indeed use zinc additives, always have so I don't know why the cam would go flat, but it is still a possibility i suppose.
 
Ok guys, I just fired it up and got temperature readings off of all the cylinders, and cylinder 5 was a bit lower than the others. with the engine running, cylinder 5 was at about 300 to 350 degrees, while the other 7 cylinders were at about 400 to 450. I don't think number 5 is a dead cylinder, but something is definitely up with it.
 
Cudafever said:
This is what i would do first! if you have a shop broom, and it has a wood handle, remove it from the brush and us it as your stethoscope. or go to the lumber yard and buy you a Wood Dowel, 1/2 diameter,4-6 foot long and us that as your stethoscope.
Click to expand...
Yep, I use a big screwdriver or a 3' wooden dowel... both make great stethoscopes.

That lower temp on #5 is interesting, OP.
 
CheeseRules01! said:
Ok guys, I just fired it up and got temperature readings off of all the cylinders, and cylinder 5 was a bit lower than the others. with the engine running, cylinder 5 was at about 300 to 350 degrees, while the other 7 cylinders were at about 400 to 450. I don't think number 5 is a dead cylinder, but something is definitely up with it.
Click to expand...
How was #7?
 
diymirage said:
Wouldn't be the first time, it's an easy mistake to make
I dont know if it would cause the knocking, but who knows
Click to expand...

I checked the firing order, they are in their correct locations. The temp on #7 was like the others, between 400 to 450 degrees. #5 was the only one I noticed with a lower temp.
 
Have you pulled the inspection cover and checked the
torque converter and flex plate yet?
 
Have not heard anyone talk about what kind of oil pressure you are running at now, at startup and after warmed up. 5 psi oil pressure at idle is not enough although better than Zero. Sounds like a lot of valve train noise in the video, that is the first thing that shows up when you are experiencing low oil pressure.

What does the oil look like when you pull the dipstick and wipe it on a white paper towel. Black and Grainy or clear like brand new oil ??? Next pull the oil filter and cut it open, you can zip around the base of the oil filter 1" up from the bottom and let the can fall off. Have a drain pan there to catch everything that comes out of it, then you can see what it has trapped out of the system before it sends the oil though the engine again. If that filter starts plugging off it will reduce your oil pressure.

Also take a magnet to the paper filter from the inside of the filter to see if it picks up any steel from parts wearing out. Seeing steel slivers in there is not a good thing, and there will be some black sludge in there too.

Can drop the engine oil out too and see what comes out of the pan.

Put fresh oil and a new oil filter and fire it up again and see if things quiet down a bit. If all checks out OK so far but still making noise, you can add 1/2 pint of Lucus Engine Oil Treatment to the oil and try again (the thick stuff like Honey . . like the STP) this should quite things down a bit as a test. Will help you determine if it is internal engine bearings or valve train, or an external item like a cracked flex plate at your torque converter.

Still have not heard that you have checked out that mechanical fuel plump yet, they will still pump fuel with the arm going loose inside sending the noise and rattle all the way down the camshaft and up through the valve train. Just think about the "Beat" of your knock, it is not like a sound that all 8 rods are slapping at the same time. It's is more like a single "Beat" of the Eccentric on the cam hammering the loose Plunger Arm on the fuel pump sending the noise down through the cam and into your block.

Can also pull the distributor cap off and see how much left to right turning distance you have on the distributor rotor. More than stock distance travel when turning left to right tells you things are getting wore out down below there, all the way down to the oil pump and distributor drive gear and bronze bushing in the block.
 
With the Distributor cap off with the rotor on, you can put a socket with a ratchet on the big bolt on the end of the crank at the pullies. See how many degrees you have to rotate the crankshaft before the rotor on the distributor starts to turn. Clockwise, counter clockwise, see how many degrees. If excessive can help zero you in on your problem.

Also what does the transmission fluid look like when you wipe the stick on a white paper towel, nice and cherry red or dark brown and burnt smelling ?? Could be issues at the front pump of the trans just behind the torque converter, things getting wore out . . . So yeah someone asked what does it sound like when you put it in gear, better or worse ???
 
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Yet another vote for checking convertor bolts if you haven't yet. It's been 25 years ago, but I think that's about what my dad's Challenger sounded like with two bolts loose between flexplate and convertor. I was sure engine was near death but it took dad all of 5 minutes to diagnose real problem.
 
George Jets said:
Have not heard anyone talk about what kind of oil pressure you are running at now, at startup and after warmed up. 5 psi oil pressure at idle is not enough although better than Zero. Sounds like a lot of valve train noise in the video, that is the first thing that shows up when you are experiencing low oil pressure.

What does the oil look like when you pull the dipstick and wipe it on a white paper towel. Black and Grainy or clear like brand new oil ??? Next pull the oil filter and cut it open, you can zip around the base of the oil filter 1" up from the bottom and let the can fall off. Have a drain pan there to catch everything that comes out of it, then you can see what it has trapped out of the system before it sends the oil though the engine again. If that filter starts plugging off it will reduce your oil pressure.

Also take a magnet to the paper filter from the inside of the filter to see if it picks up any steel from parts wearing out. Seeing steel slivers in there is not a good thing, and there will be some black sludge in there too.

Can drop the engine oil out too and see what comes out of the pan.

Put fresh oil and a new oil filter and fire it up again and see if things quiet down a bit. If all checks out OK so far but still making noise, you can add 1/2 pint of Lucus Engine Oil Treatment to the oil and try again (the thick stuff like Honey . . like the STP) this should quite things down a bit as a test. Will help you determine if it is internal engine bearings or valve train, or an external item like a cracked flex plate at your torque converter.

Still have not heard that you have checked out that mechanical fuel plump yet, they will still pump fuel with the arm going loose inside sending the noise and rattle all the way down the camshaft and up through the valve train. Just think about the "Beat" of your knock, it is not like a sound that all 8 rods are slapping at the same time. It's is more like a single "Beat" of the Eccentric on the cam hammering the loose Plunger Arm on the fuel pump sending the noise down through the cam and into your block.

Can also pull the distributor cap off and see how much left to right turning distance you have on the distributor rotor. More than stock distance travel when turning left to right tells you things are getting wore out down below there, all the way down to the oil pump and distributor drive gear and bronze bushing in the block.
Click to expand...



I changed the oil about two days before the knocking sound started, so it has nice new oil in it. I also already put the STP stuff in it, and that didn't help. Have not cut the filter open yet, I have been having some nasty weather here lately, cant go outside to do much. As far as I can tell, the torque convertor bolts are all in, and I didn't see any cracks on the flexplate. I does have a bit of a low oil pressure issue at idle, its about 5 to 10 PSI, which explains the extra noise in the valve train. Next time I have some decent weather i'll go out and check the distributor for play, as well as use a stethoscope while its running and see if I can pinpoint the noise somehow.
 
George Jets said:
With the Distributor cap off with the rotor on, you can put a socket with a ratchet on the big bolt on the end of the crank at the pullies. See how many degrees you have to rotate the crankshaft before the rotor on the distributor starts to turn. Clockwise, counter clockwise, see how many degrees. If excessive can help zero you in on your problem.

Also what does the transmission fluid look like when you wipe the stick on a white paper towel, nice and cherry red or dark brown and burnt smelling ?? Could be issues at the front pump of the trans just behind the torque converter, things getting wore out . . . So yeah someone asked what does it sound like when you put it in gear, better or worse ???
Click to expand...

The tranny fluid looks fine, nice and cherry red like you mentioned. When its in gear, the only difference is that it gets slightly quieter idling, which is probably just because the RPMs go down slightly as you put in gear as well.
 
I can tell you my car sounded like it had a rod knocking too. Looked at converter bolts and did not look like any were loose and did not see where it looked like they were hitting the dust shield but I did not put a wrench on them. Took it to a shop and $200 later they told me the converter bolts were loose. I would put a wrench on all of them.
 
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