Engine Knocking Noise
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
Engine Knocking Noise
I am getting a really loud knocking noise coming from (what sounds like) the front of the engine when it is 1)warmed up after running on the interstate and 2) at idle. This sound comes and goes..sometimes when I shut the engine off, wait a couple of minutes and restart, the knocking noise disappears. I have replaced the water pump, harmonic balancer, checked the clearance between the the water pump and pulleys AND checked the clearance between the crank shaft pulley and water pump pulley....all check out OK and the noise is still there..... 
Oil Pressure: 30-40lbs. Could it be rockers??? HELP!!!!
Oil Pressure: 30-40lbs. Could it be rockers??? HELP!!!!
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
About a month ago. That's when I saw the harmonic balancer was coming apart...replaced that. The noise still came and went. Replaced the water pump thinking the pulleys were hitting the pump....realized that the waterpump was for a regular 350 and not a Corvette 350 (difference was the flange)....
I thought it could be the rockers....but the noise really sounds like it is coming from the pulleys area....
I thought it could be the rockers....but the noise really sounds like it is coming from the pulleys area....
Burning Brakes
Joined: Nov 2005
Posts: 1,143
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From: Leander Texas
Do you have a mechanical fuel pump or not? I have had fuel pumps fail in the past, and it has sounded like a rod bearing failure. You may want to do a cylinder cut out test to check, and see if you have a wrist pin or rod bearing failing. Do you see any metal on the dip stick?
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
I have a mechanical fuel pump...it's a little over 1 year old. I change the oil every 3000 miles & check it a couple of times a week. Everything seems normal in that area....clean oil.
That's interesting about the fuel pump....how can you check to see if that's it?
That's interesting about the fuel pump....how can you check to see if that's it?
Drifting
Joined: Mar 2003
Posts: 1,608
Likes: 3
From: Canberra AUSTRALIA
St. Jude Donor '05-'06
I just had very similar simptoms. Turned out to be my conrod bearings.
First remove all the accessory belts, the fan clucth and fan. Start car. Is the noise gone? Then it is one of the accessories (water pump, alternator, PS pump, fan clutch?, AC compressor?)
Is it still noisey? Then it is internal. With insulated gloves/pliers pull one spark plug wire at a time and see if the noise changes. This takes the load of each cylinder. May indicate which cylinder is bad.
Another check is to pull the rocker covers and check all your rockers etc are tight and nothing is broken.
Good luck. Mine is still in the shop. Hopefully back this week.
First remove all the accessory belts, the fan clucth and fan. Start car. Is the noise gone? Then it is one of the accessories (water pump, alternator, PS pump, fan clutch?, AC compressor?)
Is it still noisey? Then it is internal. With insulated gloves/pliers pull one spark plug wire at a time and see if the noise changes. This takes the load of each cylinder. May indicate which cylinder is bad.
Another check is to pull the rocker covers and check all your rockers etc are tight and nothing is broken.
Good luck. Mine is still in the shop. Hopefully back this week.
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Drifting
Joined: Nov 2005
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Originally Posted by DR.Jay
Do you have a mechanical fuel pump or not? I have had fuel pumps fail in the past,
and it was the fuel pump knocking. i was able to use a long tube funnel
to isolate the problem each time just put the end of the funnel down
on the pump give a listen.
good luck
Thread Starter
Melting Slicks
Joined: Jan 2003
Posts: 2,713
Likes: 31
From: Shreveport LA
LA Events Coordinator
the knocking was the fuel pump! Stethescoped it and found it!!!! Have a new Holley 80gph overnighted from Jegs....will get it Friday and installing it the same day! Wish me luck....is there a trick to installing it?
Racer
Joined: Oct 2005
Posts: 343
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From: Rye TX
Originally Posted by vetteguy75
the knocking was the fuel pump! Stethescoped it and found it!!!! Have a new Holley 80gph overnighted from Jegs....will get it Friday and installing it the same day! Wish me luck....is there a trick to installing it?
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
Originally Posted by vetteguy75
the knocking was the fuel pump! Stethescoped it and found it!!!! Have a new Holley 80gph overnighted from Jegs....will get it Friday and installing it the same day! Wish me luck....is there a trick to installing it?
watch the fuel pressure
Melting Slicks
Joined: Aug 2003
Posts: 2,135
Likes: 2
From: Dayton Oh
Originally Posted by DR.Jay
Do you have a mechanical fuel pump or not? I have had fuel pumps fail in the past, and it has sounded like a rod bearing failure. ?
Just got thru putting on head gaskets on a friends 76, started the darn thing up and thought that I'd done something terribly wrong until I looked underneath the car and saw a small puddle of oil dripping from the fuel pump. Replaced the pump and now no oil and no sound. It was an easy 15 min job + 
Race Director
Joined: Oct 2002
Posts: 12,065
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From: Smalltownville Michigan
Cruise-In 5, 6 & 10 Veteran
St. Jude Donor '09
as for tricks, i use a long thin screwdriver inserted in one of the front mount bolt holes to hold the dowel up. i tried the longer bolt method and i had slipping problems.
Burning Brakes
Joined: Jun 2002
Posts: 837
Likes: 3
From: Texas
I think as long as the diaphram in the pump is intact it will pump. What you're hearing I believe is the action of the pump arm......some are just noisy at the end of the stroke...at least that's the conclusion I came to when mine did this. The arm on my old pump was somewhat "coined" (not sure if that made any difference) and when I tested it (just pushing the arm up and down) on a work bench the noise from the action was a spot on match for what I was hearing with the engine at idle. I didn't replace it with anything special......just an plain old AC Delco.....so far it's been quiet for 3 years.
For me replacment was a bit of a chore. I have a bad back and the thing is hard to reach from either the top or the bottom. I hear that some folks reach it through the fender well, but that wasn't much help in my case.
For me replacment was a bit of a chore. I have a bad back and the thing is hard to reach from either the top or the bottom. I hear that some folks reach it through the fender well, but that wasn't much help in my case.
Burning Brakes
Joined: Sep 2005
Posts: 1,078
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From: Santee CA
Originally Posted by AlCherry
A lot of shady mechanics sold customers motors that knocked knowing that it was the fuel pump. Chevy's were bad about it.
He told the guy that it was part of the "racing rockers, lifters, and cam" that had been installed. He should just "turn up the radio" to drown it out.
A week later the engine blew up and the guy came back to my grandfather wanting money for the car; my grandfather told him, "Hey, caveat emptor."
I'm ashamed to admit that I'm related to the man.
