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Discussion Starter · #1 ·
I have a knock and for the life of me I can't figure out where it is coming from. I have replaced the alternator, ps pump and water pump, but it's still knocking. I will try to describe it... It is not constant, but it has been getting more frequent. It happens ever time I drive now, but it will go away for brief periods of time. The knock doesn't change as rpm's change, it stays consistent. It is most noticeable at adle and is quite loud. Pretty sure it is coming from the front of the engine. The knock goes away when there are no belts on the car and I briefly start it.
Today seemed real bad and the car was acting like it wanted to die on me and was running a bit warmer than normal (maybe unrelated) it also felt like the car was shuddering every once in awhile. I'm thinking maybe harmonica balancer is bad??? But I'm tired or throwing money at it without really knowing what is causing it. Any ideas or things I can do to narrow down what it is? Heeeeelp!!
 

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If harmonic balancer were bad, I would think taking belts off engine wouldn't stop the noise. But, still, maybe the load of the belts are causing the problem.

I'd start with a cold engine, with belts off. Let engine run a little while, keeping your eye on the water temp, Run to temp gets to normal operating temp and shut engine down. Any noise happen? Also watch balancer to see if there's any wobble.

Also watch balancer with belts on and see if it wobbles. Use a stethoscope to listen to each accessory while noise is happening.
 

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']['exXxas']['itan
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Mechanical fuel pump?
 

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It would seem to me that most noises would increase with RPM if it were something tied to the front of the engine and when no belts are on some of those items no longer turn so it would seem that one of those items no longer turning would be the problem since the noise stops when no belts are on? I am grasping here and I am not trying to insult your intelligence, but you did and still have a divider plate between your water pump and timing chain cover when you replaced your water pump? And if so, you can verify that the impellers of the pump are not contacting the divider plate? if no divider plate maybe the impellers are contacting those inserts that get put into the timing chain cover?
 

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']['exXxas']['itan
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Im reaching here, but thinking under rpm the timing chain would stay tight, but under no load like idle condition it could "ratchet" if worn heavily...maybe enough to smack the fuel pump level? haven worked on a P motor in forever so cant remember how it all mounts up ect for the pump eccentric.
 

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Mechanical fuel pump?
Yes it is
It would seem to me that most noises would increase with RPM if it were something tied to the front of the engine and when no belts are on some of those items no longer turn so it would seem that one of those items no longer turning would be the problem since the noise stops when no belts are on? I am grasping here and I am not trying to insult your intelligence, but you did and still have a divider plate between your water pump and timing chain cover when you replaced your water pump? And if so, you can verify that the impellers of the pump are not contacting the divider plate? if no divider plate maybe the impellers are contacting those inserts that get put into the timing chain cover?
Yes the divider plate is still there and no it's not contacting. The sound was there before I replaced the water pump.
Another realization and thought. It seems like the sound it only really there when I am not on the gas. It seems like under load it goes away. Making me lean towards maybe the engine mounts being bad and the mount rattling or hitting something. That may explain the metal on metal sound. I was told to try and press down on the motor and see if the sound stops. Gonna try that when I get time and take a look at the mounts. Any other thoughts?
 

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Knowing how hard it is to tell exactly where a sound is coming from on an engine this might be a portential and a reach at the same time. Check your flex plate for cracks. They tend to give off a knocking type noise if there are cracks around the bolts that mount it to the crank and that noise can travel towards the front of the crank. You'll need to pull the TC cover off so you can see the flexplate and use a good flash light to shine up inside and put it in neutral and have someone spin the engine slowly. Would really be interested in finding out what it is.
 

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1968 Convertible 400, 200 4R, 1971 Formula 400 M-22 Rock Crusher, 1984 Trans Am...........
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Since it doesn't change rpm's I question that it's engine internal related. Maybe motor mount or some body bushing or bolt is loose. Something in the engine bay not bolted down tight.
 

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Discussion Starter · #13 ·
So upon further inspection I believe the harmonic balancer may be bad. It does have somewhat of a wobble to it when rotating and it looks like there is a mark on it where it keeps hitting the marker arrows. Any way to further test that it is indeed th problem?
 

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']['exXxas']['itan
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If its wobbling, I'd swap it out regardless.
 

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Exhaust will often knock when mounts are bad, and body mounts can be erratic noises too. Im betting the wobbly balancer is just a different problem
 

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So I never followed up with this. Pretty embarrassed to tell the story, but here it goes. After not being able to find the knock I took it to my friends shop so we could pull the motor (needed to be pulled anyway to replace the main seals). Before pulling we both checked everything we could think of again with belts on and belts off. Even used a stethoscope several times. No findings so we yank the motor. After we got it out we flipped it over to pull the pan and inspect things. Pulled main bearings, all looked new. Inspected the visible side of the crank, no issues. Put the wrench on the crank to turn it and inspect the other side and knock knock...take the wrench off and grab the pulley...sure enough the pulley has about a 1/4 inch play in either direction. Not sure how all 4 bolts could come loose, but they were. Guess that explains why you could really hear it under load; the belt is tight then and pulling it in one direction. Threw the motor back in and guess what, no knock. Lmao

Anyway, while the motor was out we cleaned and painted the whole thing. Threw on new timing cover, timing gears, harmonic, oil pan, and topped it off with a billet serpentine system from CVS Racing (great set up!). Also gave me a chance to detail the engine bay, paint the headers, etc... Anyway, on with some pics..

9d88bea6b00ddfac799fee4d9e5744d3_zpsirfi

bae7d2422322c0253c0d2f5055994c68_zpskn9u

fe5bafa443b0680a3de5e894674ab20a_zpszhav

7be5bfa20b28bebb67f8d2f61e06c11f_zpswl3s

41876dcef32bf4d2f2fc97b011c9ad13_zpsv0zu

64d009f2162be13cc9f59ee7e7c4d4df_zpsdpsa

d6406e5f79e87793aa14933e2cc56112_zps9svk

00cee75496a4fbfb6831fe4d38b25dc4_zpsa6mo
 

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Cool thanks for the follow up on that
 

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Glad to hear you figured it out!!
 

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']['exXxas']['itan
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Dang that motor setup looks CLEANNNNNNNNN! Deffo diggin the layout and your choice of "bling" on it.
 
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