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Old 09-15-2010, 01:15 PM
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LOUD knocking sound

I took my 65 Chevelle out for some driving around today to get some break in miles on the engine. I know it has some kind of vacuum leak that I am trying to track down. When I was almost home it stated making a LOUD knocking sound in the engine. It is a rebuilt 350.



What should I look at first? Remove the valve covers and check the rockers etc? Check torque, losness?

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Old 09-15-2010, 02:25 PM
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Check your torque converter bolts and see if they have come loose. A bolt that backs out sounds like a bad rod knock.
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Old 09-15-2010, 02:31 PM
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What is the frequency of the knock... one per revolution, one per two revolutions, or irregular?

Is it really a knock, or is it more of a tick or a tap?

Can you tell if it is nearer the top or bottom of the motor?

Do you have access to a stethoscope?
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Old 09-15-2010, 06:47 PM
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Check to make sure the flexplate and torque converter bolts are all tight. Like sqzbox said, it will sound like it's got a knock.
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Old 09-15-2010, 06:53 PM
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I am not sure about the revolution count but it not a fast multi tap sound.

It can be plainly heard on under the driver side valve cover, on the second cylander back. almost like it is hitting the cover or something there. Very prominent in that area.

I don't have an oil pressure guage on this car. The fluid level is good. I guess I need to remove the valve cover and start there.
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Old 09-15-2010, 06:59 PM
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It shouldn't be knocking under the valve cover, it should be more of a tapping or ticking sound unless a rocker is hitting the cover. Pull the valve cover, adjust the valve lash, and then start the engine with the cover of and let it run for a few seconds and see if the sound is still there.
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Old 09-15-2010, 07:03 PM
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Look close at the flexplate near the crank bolts for hairline cracks.My monte broke three of them everytime it sounded like a rod knock.
Two stockers,one after only a week.Then it broke evan an sfi B&M one but that took about 2yrs.Mine was due to using an old drag cars tranny for a daily driver every shift would throw your head over the headrest.
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Old 09-15-2010, 07:25 PM
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This is what is sounds like.

http://www.youtube.com/watch?v=DfJIp...eature=related
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Old 09-15-2010, 07:52 PM
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1. cracked flexplate
2. loose header
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Old 09-15-2010, 08:55 PM
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Sounds like something tapping against the valve cover. Irregular tap. Rocker arm has come loose?
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Old 09-16-2010, 01:34 PM
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Can the valves getting loud of tapping? At lunch I removed the valve cover and non were lose by feel but a couple were off center of the spring. I removed each one, checked the rods, rockers, etc. and all looked good. I tightened them back down and started the engine just to here and now there are a couple doing the same sound so I shut it off. My guess is that the lash, etc. was not correct on one and now needs to be done for each.

What is the process for setting the rockers? They heads were rebuilt but I am not sure what was done by the guy who put it together. Is there a certain torque that you use?
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Old 09-16-2010, 02:38 PM
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If your oil pressure is read normal. Then most likely you have a connecting rod split in two. That's what happen to my 305 and a friend with his 283.
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Old 09-16-2010, 02:45 PM
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Small block chevies don`t torque down, they are adjustable. I adjust them with the engine running. With the valve cover off and the engine at idle, if the rocker is ticking, tighten it down until it just stops to tick, then slowly back off until the ticking comes back, then slowly tighten it until the ticking stops, then give it a half turn. When a engine is new and the heads have been redone it`s not uncommon for the rockers to come out of adjustment as new parts seat up.
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Old 09-16-2010, 04:22 PM
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I readjusted the valve lash correctly and the sound it still there. I listened from all side of the engine and underneath and I swear it sounds like it is the carb. If I stand dead center over the engine I hear it straight down. If I move my head to the right the sound is still at the carb and vise versa.

What in the carb could do this?
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Old 09-16-2010, 04:48 PM
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Make sure you go though and check all your valve lash again. I missed one on my 350 a few weeks ago when i got my cam swap done and when I started it the very first time I heard this loud knocking noise and I listened around and it sound like it was hitting my valve cover and I went through my rocker arms and the one was loose. I did the valve lash on it again and it went away. Also check to make sure your headers or exhaust manifolds are tight to as they can also make a loud ticking noise.
Eric
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