SBC Mystery Knock - Team Camaro Tech
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post #1 of 28 (permalink) Old Sep 27th, 14, 12:16 PM Thread Starter
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SBC Mystery Knock

Hi guys. Can't seem to understand this one. I still have a random noise that sounds like large marbles bouncing around somewhere in the engine bay. It goes up and down with acceleration. The noise is not present 85% of the time, but when it does come around, it will do it cold or hot, and I can hear it from inside the car if I'm close to a wall like at a drive thru.

Car starts right up, oil pressure is good running and at idle, and throttle esponse is great. I swapped out the PCV, which I thought was the culprit, but the noise came back. Almost sounds like its coming from the valve covers, but I pulled the covers, adjusted the valves, and I don't hear it when I use my broom stick stethoscope.

I will say that the last time that I heard it at idle when hot, I 'thought' that I felt it choking the idle very slightly. I was thinking of changing the oil and adding some of the mystery oil to it.

Any thoughts? Thanks!

67 Black RS Coupe, 383, M21 & 10 Bolt Posi. Edelbrock E-Tech 170 Heads, 2204 Roller Cam, Air Gap Intake.
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post #2 of 28 (permalink) Old Sep 27th, 14, 01:36 PM
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Re: SBC Mystery Knock

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Originally Posted by cv2065 View Post
Hi guys. Can't seem to understand this one. I still have a random noise that sounds like large marbles bouncing around somewhere in the engine bay. It goes up and down with acceleration. The noise is not present 85% of the time, but when it does come around, it will do it cold or hot, and I can hear it from inside the car if I'm close to a wall like at a drive thru.

Car starts right up, oil pressure is good running and at idle, and throttle esponse is great. I swapped out the PCV, which I thought was the culprit, but the noise came back. Almost sounds like its coming from the valve covers, but I pulled the covers, adjusted the valves, and I don't hear it when I use my broom stick stethoscope.

I will say that the last time that I heard it at idle when hot, I 'thought' that I felt it choking the idle very slightly. I was thinking of changing the oil and adding some of the mystery oil to it.

Any thoughts? Thanks!
Is your ignition timing possibly over advanced causing your knock?

69 Camaro Z/28 RS, original Azure Turquoise, M21 & 3.73 12-bolt posi. NOM 406ci, AFR 210 heads, Straub hyd. roller cam & Dynatech 1-3/4" > 1-7/8" headers, QuickFuel 750 Annular. Photos at:
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post #3 of 28 (permalink) Old Sep 27th, 14, 01:57 PM Thread Starter
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Re: SBC Mystery Knock

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Originally Posted by NH69Z28RS View Post
Is your ignition timing possibly over advanced causing your knock?
I don't think so. I'm currently at 10 degrees BTDC, and the car starts right up and shuts down with no issues. Temp is 185 all day long.

Would rod knock be constant or could it be random? I thought perhaps as the engine reached operating temps, the oil thins out, then one would hear the knock, but the knock is random, even with a warm engine.

67 Black RS Coupe, 383, M21 & 10 Bolt Posi. Edelbrock E-Tech 170 Heads, 2204 Roller Cam, Air Gap Intake.
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post #4 of 28 (permalink) Old Sep 27th, 14, 05:26 PM
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Re: SBC Mystery Knock

Quote:
Originally Posted by cv2065 View Post
Hi guys. Can't seem to understand this one. I still have a random noise that sounds like large marbles bouncing around somewhere in the engine bay. It goes up and down with acceleration. The noise is not present 85% of the time, but when it does come around, it will do it cold or hot, and I can hear it from inside the car if I'm close to a wall like at a drive thru.

Car starts right up, oil pressure is good running and at idle, and throttle esponse is great. I swapped out the PCV, which I thought was the culprit, but the noise came back. Almost sounds like its coming from the valve covers, but I pulled the covers, adjusted the valves, and I don't hear it when I use my broom stick stethoscope.

I will say that the last time that I heard it at idle when hot, I 'thought' that I felt it choking the idle very slightly. I was thinking of changing the oil and adding some of the mystery oil to it.

Any thoughts? Thanks!
You should not have to think about changing oil, its cheap, Change it and filter and look at oil for any heavy metal, If you can , cut open the oil filter and look at the paper wrap.

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #5 of 28 (permalink) Old Sep 27th, 14, 09:01 PM Thread Starter
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Re: SBC Mystery Knock

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Originally Posted by zdld17 View Post
You should not have to think about changing oil, its cheap, Change it and filter and look at oil for any heavy metal, If you can , cut open the oil filter and look at the paper wrap.
Yes, changing the oil is cheap. I pulled the plug tonight and there was a small amount of sludge on the magnetic tip with a few hair like pieces that disintegrated between the fingers. Not uncommon. I changed it about 500 miles ago, so I'll use a little mystery oil to see if it cleans it up a bit.

My question was in regard to rod knock. I would assume that rod knock would be a constant if that were the issue, but the noise is random.

67 Black RS Coupe, 383, M21 & 10 Bolt Posi. Edelbrock E-Tech 170 Heads, 2204 Roller Cam, Air Gap Intake.
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post #6 of 28 (permalink) Old Sep 28th, 14, 07:17 AM
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Re: SBC Mystery Knock

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Originally Posted by cv2065 View Post
Yes, changing the oil is cheap. I pulled the plug tonight and there was a small amount of sludge on the magnetic tip with a few hair like pieces that disintegrated between the fingers. Not uncommon. I changed it about 500 miles ago, so I'll use a little mystery oil to see if it cleans it up a bit.

My question was in regard to rod knock. I would assume that rod knock would be a constant if that were the issue, but the noise is random.
You can do an old school test , if the noise is present at the time, remove one spark plug feed at a time , what you will be looking for is a change in sound. The absence of the spark that causing the combustion "load" to that rod may tell you what you are thinking. If its bad, it will show up .
What kind of sound is this? Deep? Light? metalliac knock or tap?
Do this with the vac advance hose disconnected if you suspect a spark knock. Actually you should not have any mechanical advance until 1500 rpm or so. You will have some advance at idle if hose is connected . If your vac hose is connected to ported vac, you wont have any until throttle plates is opened. Just disconnect the dist advance and go from there to eliminate the spark knock. You can run 10 on the crank.

When you had the valve covers off, did you look for any broken springs?

If you suspect its carbon on top of piston, pour a little LoneStar beer down the carb while the motor is running at fast idle. A little , not enuff to lock up motor. In Texas, this normally will knock off the carbon off the heads.

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #7 of 28 (permalink) Old Sep 28th, 14, 07:24 AM
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Re: SBC Mystery Knock

Do you have an oil pan windage tray? If it's a rod knock the next time it knocks, rev it up and see if when you let off the gas the knock stops.

Mark 70 Z28 M22 3.73 Z21 Z87 - Lunati 20120121 Roller Cam

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post #8 of 28 (permalink) Old Sep 28th, 14, 08:13 AM
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Re: SBC Mystery Knock

Much as I would like to help, I think you need to post a clip with good audio before anyone can do more than venture a guess.

QUOTE: In Texas, this normally will knock off the carbon off the heads.

Don, what if he is not in Texas?

Lynn
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post #9 of 28 (permalink) Old Sep 28th, 14, 08:59 AM
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Re: SBC Mystery Knock

Are you running a stroker ? 383 ?

The crank has tight clearances at the oil pan and between camshaft/rods.

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post #10 of 28 (permalink) Old Sep 28th, 14, 09:31 AM Thread Starter
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Re: SBC Mystery Knock

Thanks for the responses guys. I will definitely take a quick video the next time that it does it, but its just hard to pin down. I took it out all day yesterday, and it happened once for about a minute, then quieted down again. The sound sounds like something is knocking against the inside of a valve cover, hollow, but not too deep. Nothing looked amiss when I took the covers off (i.e. no broken springs, bent rods, etc.).

Just your typical, mild cam 350 Lawrence..nothing crazy. Although, January may be time to build my first 383...

Not sure about the beer Don...how about a bottle of YingLing or a strong Mai Tai?

67 Black RS Coupe, 383, M21 & 10 Bolt Posi. Edelbrock E-Tech 170 Heads, 2204 Roller Cam, Air Gap Intake.
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post #11 of 28 (permalink) Old Sep 28th, 14, 10:14 AM
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Re: SBC Mystery Knock

Timing chain possibly getting a little bit of play and contacting timing cover? If too much play the chain can ride up gear teeth a bit causing contact. Just an uneducated guess on my part.
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post #12 of 28 (permalink) Old Sep 28th, 14, 12:55 PM
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Re: SBC Mystery Knock

Quote:
Originally Posted by bilodeaulynn View Post
Much as I would like to help, I think you need to post a clip with good audio before anyone can do more than venture a guess.

QUOTE: In Texas, this normally will knock off the carbon off the heads.

Don, what if he is not in Texas?
Milwaukee best? Buckhorn or Pabst? That other stuff he mentioned, never heard of it. Definitely not from Texas.

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #13 of 28 (permalink) Old Sep 28th, 14, 02:48 PM
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Re: SBC Mystery Knock

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Originally Posted by zdld17 View Post
.....pour a little LoneStar beer down the carb.....
That's alcohol abuse!

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post #14 of 28 (permalink) Old Sep 28th, 14, 03:48 PM Thread Starter
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Re: SBC Mystery Knock

Ok guys. I was able to capture a couple of videos today with the knocking. The first video is from the engine bay, and I don't think that you can hear anything except the wind in the iPhone. This is when the knocking was slight, after the car was warmed up a bit.

http://s30.photobucket.com/user/cv20...e836d.mp4.html

This second video, from under the car. Sound seems to be louder when cold, but seems to always be there in some form.

http://s30.photobucket.com/user/cv20...8.mp4.html?o=0

And here's a video from the other side underneath.

http://s30.photobucket.com/user/cv20...e.mp4.html?o=0

I still can't find the noise anywhere with my homemade stethescope. You would think that it would be easy to find?

Watcha guys think?

67 Black RS Coupe, 383, M21 & 10 Bolt Posi. Edelbrock E-Tech 170 Heads, 2204 Roller Cam, Air Gap Intake.
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post #15 of 28 (permalink) Old Sep 28th, 14, 04:22 PM
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Don
 
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Re: SBC Mystery Knock

You are correct about the wind. Hard to hear, oil pump? Fuel pump? Any chance the rocker arm hitting the center bolt hold down on the valve covers?

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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