Strange unidentified knock from engine - Corvette Forum : DigitalCorvettes.com Corvette Forums
 
 
Go Back   Corvette Forum : DigitalCorvettes.com Corvette Forums > C3 Corvette Forums > C3 Corvette
Register Forums Garage Garage Mark Forums Read Auto EscrowInsurance

Notices

C3 Corvette
C3 Corvette General | Technical | Performance | Aftermarket | Discussions

Other sections:
Corvettes Classifieds
Corvette Detailing & Car Care
Corvette Audio/Video/Radar
General Automotive/Shop/Tools
Corvette Performance Driving/Racing

( Sponsored by: Zip Corvette Parts )

Shops/Tuners
Custom Image Corvettes
A&A Corvette
Corvette tuner

Interior
Corvette aftermarket products

Insurance

Parts & Products
Race Ramps
Edelbrock
ATI/Procharger
Corvetteguys.com
Melrose Motorsports
Parts Taxi
Airaid
Mid America Motorworks
Pfadt Racing
Madvette Motorsports
Hi-tech Custom Concepts
Corvette aftermarket products
Corvette Garage
Corvette Parts and Accessories
Corvette Car Care Products
Corvette HID
Mid America Motoroworks

Tracks/Schools
Bob Bondurant School of High Performance Driving
Corvette driving school

Wheels/Tires
Cray Wheels

Services
BADWERKS.com
Reply
 
Thread Tools
Old 09-04-2012, 06:43 PM   #1
AirbornSilva
DC Crew
 
Posts: 246
Member #119623
Member since: Sep 2012

Thanks: 7
Thanked 3 Times in 3 Posts
Strange unidentified knock from engine

my engine has developed a knock, I did a trick that an old timer taught me a long time ago to see if it was a rod, which is to take off one plug wire at a time from the distributor cap and if the knock goes away it's a rod and it's that cylinder, well it didn't stop. Also, this knock has been happening for I'd say a good 400 miles.

I then thought that maybe it's a sticky lifter so I put some seafoam in the engine which did quiet it down. my friend and I listened around the engine in various spots with a stethoscope but couldn't pinpoint anything.

Today I got home from work and decided to see how it sounds, well after startup it really wasn't better than before, maybe a little, but after it warmed up it did quiet down again quite a bit but was still there.

Any ideas, wrist pin maybe?
AirbornSilva is online now   Reply w/quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 09-04-2012, 08:40 PM   #2
iburke
Sir Dude
 
iburke's Avatar
 
Posts: 17,397
Member #6081
Member since: Dec 2003
Location: St Joseph MO.

My Corvette(s)
1971 T-Top

Thanks: 38
Thanked 57 Times in 44 Posts
Can you make a video file so we can hear it?
iburke is offline   Reply w/quote Quick reply to this message
I can't tell if I'm dealing well with life these days or I just don't give a shit any more.
Old 09-05-2012, 02:56 AM   #3
AirbornSilva
DC Crew
 
Posts: 246
Member #119623
Member since: Sep 2012

Thanks: 7
Thanked 3 Times in 3 Posts
Yes, I'll get that up as soon as i can. Thank you for the reply!
AirbornSilva is online now   Reply w/quote Quick reply to this message
Old 09-05-2012, 06:46 AM   #4
Texdentist
 
Texdentist's Avatar
 
Posts: 18,386
Member #76657
Member since: Oct 2008
Location: Crowley, TX

My Corvette(s)
2013 Coupe, 2009 Coupe - traded, '74 Coupe totalled, '77 Coupe sold

Thanks: 43
Thanked 516 Times in 372 Posts
If it's an automatic, consider a cracked flexplate. Those things make a hard knocking sound that sometimes gets better at higher RPM, and they are hard to localize the sound on.
Texdentist is online now   Reply w/quote Quick reply to this message
Old 09-05-2012, 06:57 AM   #5
Altered
DC Crew
 
Altered's Avatar
 
Posts: 2,309
Member #67645
Member since: Dec 2007
Location: Texas

My Corvette(s)
1976 Stingray L48 4spd

Thanks: 54
Thanked 64 Times in 55 Posts
Garage
I have seen a screw that holds the choke in place fall out and stick in the top of a piston once. Might take a look at the choke and make sure all the screws are still in place.
Altered is offline   Reply w/quote Quick reply to this message
Quote:
Originally Posted by MR BRNS C6 View Post
Living in California is sort of like surfing the internet. When you think you've seen the worst shit ever and nothing could possibly top it, something comes along and tops it.
Old 09-05-2012, 07:38 AM   #6
AirbornSilva
DC Crew
 
Posts: 246
Member #119623
Member since: Sep 2012

Thanks: 7
Thanked 3 Times in 3 Posts
It's a 4 speed... I will check for missing screws on the carb to see if there may be any possible MIA screws.

Thanks guys!
AirbornSilva is online now   Reply w/quote Quick reply to this message
Old 09-05-2012, 11:27 AM   #7
graphicjunki
DC Crew
 
graphicjunki's Avatar
 
Posts: 463
Member #118654
Member since: Apr 2012
Location: CO, USA!

My Corvette(s)
75 Stingray

Thanks: 15
Thanked 15 Times in 15 Posts
Garage
Could be a crapped out lifter - How's that for tech terms?

Take off the valve covers. If you don't have one, get a cheap-o mechanic's stethoscope from Harbor Freight. Start the engine and put the stethoscope on one rocker center post at a time. If it's a collapsed lifter, you will hear it.

Couple that with what's been said about the spark plug wires and that will narrow it down to top or bottom end pretty much.
graphicjunki is online now   Reply w/quote Quick reply to this message
WillyB - 1975
L48 Bore'd and cam'd - vortec - Dougs headers and side pipes - 200R4 - e-fan - quicksilver

**Coming!**
Spirals
406

http://photobucket.com/Willys75Stingray
Old 09-05-2012, 11:40 AM   #8
gkull
DC Crew
 
gkull's Avatar
 
Posts: 588
Member #44069
Member since: Mar 2006
Location: Nevada

My Corvette(s)
1979 Highly Modded

Thanks: 0
Thanked 1 Time in 1 Post
Is this a modified motor? Like rebuilt with kb hypereutectic pistons?

I saddly found out years ago that they have a heat and Feet Per Second limitation. I was driving it hard at higher rpm for a period of time (going fast) when I let off the gas i had what you would think was rod knock, but the odd thing is it had good oil pressure. If you have bearing failure the oil pressure goes very low or even to zero.

I had friends listen to it and upon tear down the piston had smeared the aluminum. Locking the rings tight in the piston. So it had a bad case of piston slap.

A drag strip a fellow racer in the pits had N20 150 hp spray bar and he had bad detonation going down the track. When he came in it sounded like my piston slap. But detonation had actually broken the outer piston crown away and broke the rings
gkull is offline   Reply w/quote Quick reply to this message
Old 09-05-2012, 11:59 AM   #9
AirbornSilva
DC Crew
 
Posts: 246
Member #119623
Member since: Sep 2012

Thanks: 7
Thanked 3 Times in 3 Posts
Quote:
Originally Posted by gkull View Post
Is this a modified motor? Like rebuilt with kb hypereutectic pistons?

I saddly found out years ago that they have a heat and Feet Per Second limitation. I was driving it hard at higher rpm for a period of time (going fast) when I let off the gas i had what you would think was rod knock, but the odd thing is it had good oil pressure. If you have bearing failure the oil pressure goes very low or even to zero.

I had friends listen to it and upon tear down the piston had smeared the aluminum. Locking the rings tight in the piston. So it had a bad case of piston slap.

A drag strip a fellow racer in the pits had N20 150 hp spray bar and he had bad detonation going down the track. When he came in it sounded like my piston slap. But detonation had actually broken the outer piston crown away and broke the rings
I just bought this so I can't say what if anything has been done to the engine but it is doubtful anything has.

It has great oil pressure, 40lbs at operating temp and RPM's, and after adding seafoam it quiets down once warm, I am at a loss and appreciate all sugestions..
AirbornSilva is online now   Reply w/quote Quick reply to this message
Old 09-05-2012, 12:24 PM   #10
1963SS
DC Crew
 
1963SS's Avatar
 
Posts: 2,121
Member #96709
Member since: Dec 2009
Location: Eastern, KY

My Corvette(s)
1995 C4

Thanks: 48
Thanked 255 Times in 149 Posts
I'm certain that some of the folks on this forum will know what the "knocking" noise is once it can be heard. You really need to give us a video or a sound clip because there are a gazillion knocking sounds that can come from the engine. Some are dull knock, ringing knock, sharp knock, etc and they all sound different.

What kind of oil pressure when hot and cold whilst idling? The Seafoam and the warm idling thingy is a bit curious though. Need a video......badly, otherwise we're just shooting in the dark.
1963SS is online now   Reply w/quote Quick reply to this message

I can only dream of a world where a chicken can cross the road without having his morals questioned.

Old 09-05-2012, 12:46 PM   #11
AirbornSilva
DC Crew
 
Posts: 246
Member #119623
Member since: Sep 2012

Thanks: 7
Thanked 3 Times in 3 Posts
Quote:
Originally Posted by 1963SS View Post
I'm certain that some of the folks on this forum will know what the "knocking" noise is once it can be heard. You really need to give us a video or a sound clip because there are a gazillion knocking sounds that can come from the engine. Some are dull knock, ringing knock, sharp knock, etc and they all sound different.

What kind of oil pressure when hot and cold whilst idling? The Seafoam and the warm idling thingy is a bit curious though. Need a video......badly, otherwise we're just shooting in the dark.
Roger that, will try to get a video tonight
AirbornSilva is online now   Reply w/quote Quick reply to this message
Old 09-05-2012, 03:25 PM   #12
iburke
Sir Dude
 
iburke's Avatar
 
Posts: 17,397
Member #6081
Member since: Dec 2003
Location: St Joseph MO.

My Corvette(s)
1971 T-Top

Thanks: 38
Thanked 57 Times in 44 Posts
make a good compression test on all cylinders...
iburke is offline   Reply w/quote Quick reply to this message
I can't tell if I'm dealing well with life these days or I just don't give a shit any more.
Old 09-05-2012, 05:47 PM   #13
AirbornSilva
DC Crew
 
Posts: 246
Member #119623
Member since: Sep 2012

Thanks: 7
Thanked 3 Times in 3 Posts
Here's the videos, not sure in what order but I tell you in the video. I don't think the video shows a lot of difference though but you can really tell a difference in person.... CAUTION you need a high speed connection




AirbornSilva is online now   Reply w/quote Quick reply to this message
Old 09-05-2012, 10:10 PM   #14
TMTNET
DC Crew
 
TMTNET's Avatar
 
Posts: 61
Member #59214
Member since: Apr 2007
Location: Ohio

My Corvette(s)
1978

Thanks: 0
Thanked 0 Times in 0 Posts
FWIW It sure sounds like a valve train noise to me.
TMTNET is offline   Reply w/quote Quick reply to this message
Old 09-06-2012, 12:14 PM   #15
7TRoadster
DC Crew
 
7TRoadster's Avatar
 
Posts: 1,031
Member #106320
Member since: May 2010
Location: Kennewick, WA

My Corvette(s)
1970 Roadster, Mast Motorsports LS7, TKO 600, SS Frame, C4 suspension

Thanks: 15
Thanked 43 Times in 41 Posts
I had an engine once that developed a knock like this one. It turned out to be excess slag on the side of one of the cam lobes hitting a lifter.

Ugly problem took forever to discover the cause.
7TRoadster is online now   Reply w/quote Quick reply to this message
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Corvette Forum : DigitalCorvettes.com Corvette Forums forums, you must first register.
Please enter your desired user name (12 CHARACTERS MAXIMUM), your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Powered by vBadvanced CMPS v3.2.2

All times are GMT -6. The time now is 11:02 AM.




Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.
2003-2011, DigitalCorvettes.com - All Rights Reserved