[C1] Knocking Noise
01-14-2019, 06:51 PM
#1
Racer
Thread Starter
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
01-14-2019, 06:54 PM
#2
Le Mans Master
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
01-14-2019, 07:15 PM
#3
Racer
Thread Starter
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; 01-14-2019 at 07:16 PM.
01-14-2019, 07:27 PM
#4
Race Director
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.
01-14-2019, 10:15 PM
#7
Le Mans Master
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
01-15-2019, 06:35 AM
#10
Team Owner
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...
01-15-2019, 11:10 AM
#11
Racer
Thread Starter
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
01-15-2019, 11:20 AM
#12
Race Director
Member Since: Mar 2009
Location: Canada's capital
Posts: 19,777
Received 4,583 Likes
on
2,157 Posts
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. 
01-15-2019, 12:34 PM
#13
Team Owner
I upload my videos to YouTube. Publish them in Public mode then provide a link to them in my forum post. It’s never failed.
01-15-2019, 12:53 PM
#14
Burning Brakes
Member Since: Aug 2013
Location: palm springs ca
Posts: 1,063
Likes: 0
Received 314 Likes
on
178 Posts
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
01-15-2019, 02:07 PM
#15
Racer
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; 01-15-2019 at 02:20 PM.
01-15-2019, 09:35 PM
#16
Racer
Thread Starter
01-15-2019, 10:18 PM
#17
Race Director
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..
01-16-2019, 12:24 AM
#18
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
01-16-2019, 07:12 AM
#19
Tether Man
Member Since: Dec 2004
Location: Pittsburgh, South Hills
Posts: 4,536
Received 2,014 Likes
on
1,039 Posts
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.
01-16-2019, 07:19 AM
#20
Team Owner
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; 01-16-2019 at 08:32 AM.