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Old 07-19-2007, 09:58 AM
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Knocking then Whistling

Well my SBC 350 is making a knocking noise. I believe it is coming from the motor but if you put your ear on the fender you can hear like a rattle.

I tried adjusting the timing and when advancing the knocking would go w/ the RPM's and then it would soon turn into a whistling noise until I retarded it, then it would go back to knocking.

I do not know what this could be be, any help would be appreciated

Thanks

51 Chevy Deluxe 350/350

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Old 07-19-2007, 07:59 PM
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whistling sounds like vaccume leak............ maybe your advance is busted and your getting detonation.
Shane
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Old 07-27-2007, 11:39 PM
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Ok well I tried the starting fluid method and it did nothing and I also hooked a vacuum guage up to the manifold and am getting readings around 12 and it moves like it is scenario 11 on this web page http://www.secondchancegarage.com/public/186.cfm but from 12 to 11 to 13 I tried adjusting the timing but it still does it. Also its got an HEI ignition

I believe my readings should be around 15, also how can I tell if the advance is busted
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Old 07-28-2007, 09:13 AM
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Ok well I've got it narrowed down to it only starts to knock after the car has warmed up, during the warm up when it is cold, no knocking noise???
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Old 07-28-2007, 11:11 AM
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Try this remove ALL vacuum lines and plug them. See if your problem clears up. if not then warm the motor up and remove one spark plug wire at a time.....change wire while the motor isnt running or with hi voltage pliers if your brave. if when you remove a plug wire that cylinder has the knock. If it cant be narrowed down that way.......post back......you may have troubles more than I have ever delt with.


BTW my F150 4.2 truck blew a head gasket and bent a rod.....its been knocking for about 3 years.
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Old 07-28-2007, 11:50 AM
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ok plugged vacuum lines and nothing and did the plug check but none of them stopped the knocking, it still knocked w/ each one off???

I'm stumped and open to all suggestions at this point
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Old 07-28-2007, 12:05 PM
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Ok well its wierd, I just did another check by putting the car in gear and it seems as if the knocking goes away. I also had the car revved up to about 13-1400 RPM's while in gear and holding the brakes and it didn't come back, but as soon as it was put back into park, the knocking came back
I am stumped
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Old 07-28-2007, 12:09 PM
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Remove the valve covers and make sure all the valves are opening and none of your pushrods are bent........

If all thats ok......take all the belts off and make sure it isnt a watter pump or alt.
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Old 07-28-2007, 12:22 PM
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Ok well before removing valve covers, I decided to give the belt a try , so I pulled it off and the noise seemed to not appear, can an alternator make this kind of knocking noise???
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Old 07-28-2007, 12:22 PM
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Id just about garrantee it.....you've got a cracked flexplate or a tq converter thats about to come apart.
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Old 07-28-2007, 12:24 PM
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well.....I realy dont know....sense i'm not standing over the motor....hand spin your WP and Alt and see if theres any clicking or hard places in them.
If when you put it in gear and it stops....sounds like a flexplate issue.
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Old 07-28-2007, 12:47 PM
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Ok well I took it off, started it no noise, put it back on, knocking, took it off again, no noise, put it back on, knocking.

I tried free spinning by hand and it doesn't feel like its binding anywhere , but if I shake it back and forth like to and from the alternator i can get a clicking noise, water pump makes no noise and I just replaced that not too long ago
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Old 07-28-2007, 02:08 PM
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well.....dang....thats a tough one...is the alt and WP the only accessories on the motor? If so it might pay to try another alt if you have one lieing around or go get one from your local NAPA (or other auto part store). I'v heard of alts doing this before. but you can useuly feel the place thats making noise in them.


also see if you can move the alt shaft up and down.
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Old 07-28-2007, 02:18 PM
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knocking then whistling

have you checked the lifters
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Old 07-28-2007, 07:35 PM
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Quote:
Originally Posted by Holder350
Id just about garrantee it.....you've got a cracked flexplate or a tq converter thats about to come apart.

Ok just came out from under the car and the bolts are tight and the plate and converter have no play in them. From what I can see I can't see any cracks unless their small or I missed them.

My next question is isn't there a certain way the converter is supposed to be mounted to the flexplate?

If that was wrong could it cause this noise??
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