396, 4 speed Muncie. The sound started after I flushed the coolant system and started the motor. I shut it off and restarted it and the knocking sound almost went completely away. It sounds like it’s coming from the distributor area. Any help is appreciated.
Knocking Noise
Mcmasso1
1 - 20 of 26 Posts
396, 4 speed Muncie. The sound started after I flushed the coolant system and started the motor. I shut it off and restarted it and the knocking sound almost went completely away. It sounds like it’s coming from the distributor area. Any help is appreciated.
Joined
·
2,503 Posts
I'd start with removing both valve covers. Maybe a broken rocker arm stud if you are lucky.
Rick
Rick
It didn’t before I flushed it. Now the sound is very very subtle.
As Rick said in post #2, remove the valve covers to see if you find anything obvious. Look close with a bright light at the edges and corners of the rocker arms to check for metal to metal signs and nicks, and also make sure that none of the rocker arm nuts are loose. Then look close a the inside of the valve covers for contact marks.
NEXT: (if you've rules out the rocker arms and valve covers) fire up the engine, and get it to the rpm it makes the noise( if it doesn't do it at idle rpm) which might require you to get a hand from a buddy. While the engine is making that noise, pull one spark plug boot off to see if the knocking noise stops. If it doesn't, then replace the boot, and pull the next boot off. Keep doing that one at a time. If the noise stops with any one of the plug boots being pulled off, with the engine running, and it returns as soon as the boot is replaced back onto the spark plug, then the corresponding cylinder is in question, and one of the likely possibilities for the noise in that case would be a worn connecting rod bearing that needs replacement.
What about the oil pan? Have you recently replaced it?
NEXT: (if you've rules out the rocker arms and valve covers) fire up the engine, and get it to the rpm it makes the noise( if it doesn't do it at idle rpm) which might require you to get a hand from a buddy. While the engine is making that noise, pull one spark plug boot off to see if the knocking noise stops. If it doesn't, then replace the boot, and pull the next boot off. Keep doing that one at a time. If the noise stops with any one of the plug boots being pulled off, with the engine running, and it returns as soon as the boot is replaced back onto the spark plug, then the corresponding cylinder is in question, and one of the likely possibilities for the noise in that case would be a worn connecting rod bearing that needs replacement.
What about the oil pan? Have you recently replaced it?
Joined
·
18,738 Posts
Check that rotor. What catches my ear is that it is NOT entirely RPM related, so I am thinking distributor weights and something way unsat under the cap. It slows down after the rpms do. ( and maybe that negates the distributor as the culprit?) It'll be obvious once you pull the cap. Look for traces on the inside.
If not, then pull the valve covers.
PS my "trick" mechanics stethoscope is a 3' length of fuel line. It WILL isolate the noise.
If not, then pull the valve covers.
PS my "trick" mechanics stethoscope is a 3' length of fuel line. It WILL isolate the noise.
Motor doesn't sound like it has a miss. I would first make sure you didn't advertently push on dist cap which is easy to knock cap off alignment, I have done that a few times myself with the hei cap.
Joined
·
277 Posts
How does your oil filter look? Have you been making metal?
Pull all the spark plugs and check for crud. Perhaps borescope the cylinders to rule out a bad piston ring.
In truth it kinda sounds like really bad piston slap assuming you aren't making metal, otherwise I'd say you have a bearing issue somewhere.
Pull all the spark plugs and check for crud. Perhaps borescope the cylinders to rule out a bad piston ring.
In truth it kinda sounds like really bad piston slap assuming you aren't making metal, otherwise I'd say you have a bearing issue somewhere.
Joined
·
238 Posts
Use a short piece of garden hose as a stethoscope to help isolate the noise.
Joined
·
277 Posts
I forgot to mention.... there is a possibility of a bad throw out bearing as well.
Joined
·
6,021 Posts
That sounds unusual just from a coolant change. All advice above is free which is good, but time consuming and has to be done. Make a check off list so nothing gets left out.
I would add, as you remove the valve covers look for witness marks on the inside of the covers.
I use a stethoscope all the time. Even just listening to valve train during routine maintenance. You can also move it along the side of the block but make sure you have arm and hand protection from heat.
Almost forgot. I had a distributor rotor come loose once. It was hitting the inside of the cap.
Rick
I would add, as you remove the valve covers look for witness marks on the inside of the covers.
I use a stethoscope all the time. Even just listening to valve train during routine maintenance. You can also move it along the side of the block but make sure you have arm and hand protection from heat.
Almost forgot. I had a distributor rotor come loose once. It was hitting the inside of the cap.
Rick
1968 Malibu Sport Coupe, 489c.i. 590hp 600tq, TCI 200r4 Freakshow 3,600 stall, 3.73 12 bolt posi
Joined
·
15,653 Posts
If inside the BH start the car in neutral, listen for the noise then slowly press on the clutch pedal to see if the noise goes away, if it does time to check clutch, pres plate, throw out bearing, could be a bad throw out bearing, check pilot bearing and bolts that hold flywheel and flywheel cond, also check the starter if it came loose, sounds like somethings loose
No noise change when pressing in the clutch.
1 - 20 of 26 Posts
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
-
?
