[C1] Knocking Noise
Thread Starter
Racer
Joined: Aug 2013
Posts: 345
Likes: 29
From: Starkville Mississippi
Knocking Noise
i didn’t start my car for two months. When I came home and cranked it, the knock began. Sounds like someone is tapping inside the engine with a small hammer. I understand the difficulty in diagnosing from audio/video but I don’t have much experience in this type issue and was hoping someone would have an idea about the knocks origin. I have listened to every spot on the motor valve covers, intake, block, heads, water and fuel pumps, timing cover, etc., and only hear normal mechanical sounds with my stethoscope. I assumed it might be a crank bearing but thought I should have been able to hear evidence. Any thoughts appreciated. Jim
Race Director
Joined: Mar 2018
Posts: 10,697
Likes: 2,166
From: Golden Colorado
i didn’t start my car for two months. When I came home and cranked it, the knock began. Sounds like someone is tapping inside the engine with a small hammer. I understand the difficulty in diagnosing from audio/video but I don’t have much experience in this type issue and was hoping someone would have an idea about the knocks origin. I have listened to every spot on the motor valve covers, intake, block, heads, water and fuel pumps, timing cover, etc., and only hear normal mechanical sounds with my stethoscope. I assumed it might be a crank bearing but thought I should have been able to hear evidence. Any thoughts appreciated. Jim
Thread Starter
Racer
Joined: Aug 2013
Posts: 345
Likes: 29
From: Starkville Mississippi
Thanks, I failed to mention I had pulled the wires at the distributor. No change. I also see my video didn’t load.
Last edited by Jhemp3; Jan 14, 2019 at 07:16 PM.
Race Director
Joined: Aug 2004
Posts: 15,304
Likes: 2,263
From: NorCal
Could it be a hydraulic lifter that drained down while it sat for an extended period ? Did you actually get it to start up, or just crank it over ? If it started up how long did you let it run?
Sometimes a weak lifter will drain down when it sits for an extended period of time and then pump
back up after running. It will be noisy until it pumps back up.
Sometimes a weak lifter will drain down when it sits for an extended period of time and then pump
back up after running. It will be noisy until it pumps back up.
Le Mans Master
Joined: Feb 2014
Posts: 8,911
Likes: 5,458
From: Richardson Texas
Read these two current threads. One has the answer to the other...just another area to check.
https://www.corvetteforum.com/forums...e-problem.html
https://www.corvetteforum.com/forums...blem-post.html
https://www.corvetteforum.com/forums...e-problem.html
https://www.corvetteforum.com/forums...blem-post.html
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,146
Army
Without hearing the video I'm gonna say a wrist pin or bearing. Rod knock is pretty distinctive from a collapsed lifter. A lifter is more of a clacking higher in the engine... Anyway - this is a solid lifter car. I'd still pop the valve covers off and do a physical inspection. A member here recently found a cracked-in-half rocker in his mill...
Thread Starter
Racer
Joined: Aug 2013
Posts: 345
Likes: 29
From: Starkville Mississippi
Thanks all. Can’t get video to load also having trouble posting. I’m sure my problem and not forum. My next move will be to check valves and maybe drain and check out oil for filings. This a four speed car. Oil pressure is good. ZR-1 Valvolene. (20-50) car stays in 68* garage. Will be out of town on business for a week. I’ll check back when return. Appreciate the current posts. Thanks again, Jim
Race Director
Joined: Mar 2009
Posts: 19,777
Likes: 4,592
From: Canada's capital
2020 Corvette of the Year Finalist (appearance mods)
C1 of Year Finalist (appearance mods) 2019
Just for interest when you're under the car put your ear/stethoscope to the area of the rear main and clutch cover. Mine started making a racket when the inspection cover started making contact with the rear of the crank......after I changed the starter a few weeks earlier. 
Burning Brakes
Joined: Aug 2013
Posts: 1,071
Likes: 322
From: palm springs ca
Had a few hard to find knocks in my day. 1 was a broken fuel pump spring, another was a loose pulley on the harmonic, and another was a cracked pulley.
Just a few found before a tear down. had a tinny one that was the clutch dust cover hitting thecrank.
Dom
Just a few found before a tear down. had a tinny one that was the clutch dust cover hitting thecrank.
Dom
Pro
Joined: Mar 2007
Posts: 569
Likes: 176
From: Allentown PA
BTW - it was also quite a surprise when I found out what those babies cost for the HP 327, but much better than a rebuild
edit: just saw the thread on Lars fix for warrenmj with same issue. Check that one out also
Last edited by bbxlr8; Jan 15, 2019 at 02:20 PM.
Thread Starter
Racer
Joined: Aug 2013
Posts: 345
Likes: 29
From: Starkville Mississippi
Race Director
Joined: Oct 2008
Posts: 19,212
Likes: 1,671
From: Long Island
It sounds strange on my computer, would like to know what others think. I have an opinion based on the spacing of the knock ,, not sure though..
I would do the easy first - pull the valve covers and check springs and rockers..
I would do the easy first - pull the valve covers and check springs and rockers..
Drifting
Joined: Jan 2013
Posts: 1,772
Likes: 196
From: Asheville NC
I am referring to the occasional "Hard Knock" during the video. It sounds really solid and random
Does it change with the clutch pushed in?
Does it change under load (if you put it in 3rd gear and slowly let out the clutch)
Does it change with all the belts removed
Phil
Does it change with the clutch pushed in?
Does it change under load (if you put it in 3rd gear and slowly let out the clutch)
Does it change with all the belts removed
Phil
Le Mans Master
Joined: Dec 2004
Posts: 5,394
Likes: 2,768
From: Pittsburgh
2024 C2 of the Year Finalist - Modified
2023 C2 of the Year Finalist - Modified
2022 C2 of the Year Finalist - Unmodified
2019 C1 of Year Finalist (appearance mods)
Not consistent or timed.....Sounds like the "little fella" in there hammering with a rubber mallet. Prior to the video, I was going to mention fuel pump (Post #14) if on the right engine side.
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,146
Army
That is random and does not sound like wrist pin or bearing knock to me....doesn't have the tinny sound of an inspection cover or timing chain cover "hit" either...
Its almost like something occasionally hitting a valve cover maybe and it seems louder near the dipstick to me. I'd absolutely be removing the valve covers for a look-see...
I would also do the spark plug wire "pull while running" test...you should get about 50-100RPM drop in idle speed (just to eliminate a plain old "miss" as the issue) and if the noise abates then I'd say its a bearing - a wrist pin often has a sort of a double knock. Again, I don't think its either of those though.
This is a long, long shot but I'd check that fuel pump pin in the actuator arm to see if its "walking out"...
Its almost like something occasionally hitting a valve cover maybe and it seems louder near the dipstick to me. I'd absolutely be removing the valve covers for a look-see...
I would also do the spark plug wire "pull while running" test...you should get about 50-100RPM drop in idle speed (just to eliminate a plain old "miss" as the issue) and if the noise abates then I'd say its a bearing - a wrist pin often has a sort of a double knock. Again, I don't think its either of those though.
This is a long, long shot but I'd check that fuel pump pin in the actuator arm to see if its "walking out"...
Last edited by Frankie the Fink; Jan 16, 2019 at 08:32 AM.