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[C1] Knocking Noise

 
Old 01-14-2019, 07:51 PM
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Jhemp3
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Default Knocking Noise

i didnít 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 donít 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
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Old 01-14-2019, 07:54 PM
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Originally Posted by Jhemp3 View Post
i didnít 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 donít 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
1st thing to do is warm up engine and then pull off plug wires one at a time while running and see if it quits. This will isolate it to one cylinder. Possible rod bearing or wrist pin if this happens. Good luck.
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Old 01-14-2019, 08:15 PM
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Originally Posted by Vette5311 View Post

1st thing to do is warm up engine and then pull off plug wires one at a time while running and see if it quits. This will isolate it to one cylinder. Possible rod bearing or wrist pin if this happens. Good luck.
Thanks, I failed to mention I had pulled the wires at the distributor. No change. I also see my video didnít load.

Last edited by Jhemp3; 01-14-2019 at 08:16 PM.
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Old 01-14-2019, 08:27 PM
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tuxnharley
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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.
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Old 01-14-2019, 10:16 PM
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Thanks, Tux. This is a solid lifter car. Let it run until it warmed up. No difference in knock.
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Old 01-14-2019, 10:46 PM
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Stick or automatic? I had a cracked flex plate once that sounded just like a rod knock.
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Old 01-14-2019, 11:15 PM
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leif.anderson93
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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
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Old 01-15-2019, 02:58 AM
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Westlotorn
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As mentioned pulling plug wires can make a spun rod bearing quiet down. What is your oil pressure reading? Is it normal for your engine?
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Old 01-15-2019, 04:33 AM
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Randy G.
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Mine had a knock when I bought it for a steep discount. Turned out to be a bent fuel pump arm.
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Old 01-15-2019, 07:35 AM
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Frankie the Fink
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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...
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Old 01-15-2019, 12:10 PM
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Thanks all. Canít get video to load also having trouble posting. Iím 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. Iíll check back when return. Appreciate the current posts. Thanks again, Jim
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Old 01-15-2019, 12:20 PM
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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.
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Old 01-15-2019, 01:34 PM
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Frankie the Fink
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I upload my videos to YouTube. Publish them in Public mode then provide a link to them in my forum post. Itís never failed.
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Old 01-15-2019, 01:53 PM
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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
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Old 01-15-2019, 03:07 PM
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Originally Posted by domenic tallarita View Post
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
My knock that gave me an oh sh*t period took me a while to find on my L79. Turned out to be slipping/failing harmonic balancer ring hitting. It really, really, REALLY sounded like it was coming from the crank / bottom end (...close and very hard to isolate esp. w/ sidepipes).

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 03:20 PM.
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Old 01-15-2019, 10:35 PM
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Thanks to Frankieís suggestion, I have been able to upload my engine knock video to YouTube. To listen, click on the link above. Just for the record Iíve pretty much tried all the suggested diagnostic suggestions. I certainly could have miss assessed some of the tests but at witts end. Iíve listened to most every available spot with my stethoscope and no luck. Maybe the video/audio will provide some clue. Jim
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Old 01-15-2019, 11:18 PM
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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..
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Old 01-16-2019, 01:24 AM
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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
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Old 01-16-2019, 08:12 AM
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dcamick
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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.
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Old 01-16-2019, 08:19 AM
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Frankie the Fink
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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"...

Last edited by Frankie the Fink; 01-16-2019 at 09:32 AM.
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