• Welcome to SVTPerformance!

99 With a "Knock" "Tap"

Discussion in 'New Edge Cobras' started by Lawman67, Aug 6, 2019.

  1. Lawman67

    Lawman67 New Member

    Messages:
    6
    Joined:
    Aug 4, 2019
    Location:
    Iowa
    I've read quite few posts that let me know I'm not alone on a deal I stepped into, so here's the short version:
    I picked up a 1999 Cobra Convertible 5-SPD (Black/Black) with 75K on it and new tires for 2500. Bought it off a friend that had it since new to get it out of his barn after his son brought it home one night with a very clear knock. It starts and runs, shows normal oil pressure...but it has an issue needing dealt with that I'd describe as a knock...some would say it's more of a heavy tap.... Not certain what that issue is, or what my plan is, but bought it figuring worst case scenario (motor gone) as a possible step in my recovery process from selling my 1969 Mach 1 30 years ago to buy an S-10 for college...darn.
    I am mechanically inclined enough to do quite a bit but time challenged. I'd like to figure out what I'm likely dealing with to get a version of a plan working. Not building something for the track and not a daily driver, just something to bring back to life with better internals and likely working into a super charger and still able to keep the same transmission, rear end etc...

    Here's a video sound clip...if it helps for those who have been here before.
     
  2. PaxtonShelby

    PaxtonShelby TKSDABOD Established Member

    Messages:
    5,430
    Joined:
    Nov 16, 2010
    Location:
    Pittsburgh, PA
    Does it get quieter and lower-pitched once the engine reaches operating temperature? And does it return when you rev the motor?

    My guess is rod knock. Sounds like my ‘05 Aviator that I sold yesterday.
     
  3. slo984now

    slo984now AKA 01yellerCobra Established Member

    Messages:
    14,901
    Joined:
    Oct 5, 2005
    Location:
    San Diego
    I can't watch the video as I'm at work, but the first thing I would do is drain the oil and look for glitter.
     
  4. wkornf

    wkornf Member Established Member

    Messages:
    89
    Joined:
    Mar 10, 2016
    Location:
    PBG
    I've never heard a rod knock like that. maybe a follower popped off or something. or timing chain is loose.


    Sent from my SM-G930V using Tapatalk
     
  5. Lawman67

    Lawman67 New Member

    Messages:
    6
    Joined:
    Aug 4, 2019
    Location:
    Iowa
    I haven't ran it up to temp. Just long enough to trailer and un-trailer. Didn't want to stay running at first from a cold start. It was hard to keep running while loading it on the trailer, but once it has ran for a few minutes, it would hold idle, but the noise didn't seem to lessen or change other than going faster if the RPM's go up of course.
     
  6. Lawman67

    Lawman67 New Member

    Messages:
    6
    Joined:
    Aug 4, 2019
    Location:
    Iowa
    Hmmm, worth pulling a valve cover or what would a guy look for?
     
  7. tharv71

    tharv71 New Member Established Member

    Messages:
    13
    Joined:
    Jul 13, 2019
    Location:
    Tallmadge, OH
    Sounds kind of odd for a rod knock. Really loud and tinny. Draining the oil seems like a good & easy check. If there's flakes, it needs to come apart no matter what....

    Does the noise change if you "kill a cylinder"? i.e. disconnect a coil?

    Any different while driving? Or with the clutch in or out?
     
  8. decipha

    decipha EFI Dyno Tuning Established Member

    Messages:
    633
    Joined:
    Jul 12, 2008
    Location:
    New Orleans, LA
    the most common tap noise that plagues the 4v engines is a failed timing chain tensioner which is caused when someone doesn't run a motorcraft oil filter

    never heard one sound like that before though.

    Best option is to yank the engine and pull the timing cover off to inspect.
     
  9. decipha

    decipha EFI Dyno Tuning Established Member

    Messages:
    633
    Joined:
    Jul 12, 2008
    Location:
    New Orleans, LA
    the most common tap noise that plagues the 4v engines is a failed timing chain tensioner which is caused when someone doesn't run a motorcraft oil filter

    never heard one sound like that before though.

    Best option is to yank the engine and pull the timing cover off to inspect.
     
  10. bigja01cobra

    bigja01cobra Active Member Established Member

    Messages:
    249
    Joined:
    Aug 17, 2009
    Location:
    Jackson, TN
    get an automotive stethoscope and probe while it is running it should help with narrowing down where the noise is coming from.
     
    Lawman67 likes this.
  11. wkornf

    wkornf Member Established Member

    Messages:
    89
    Joined:
    Mar 10, 2016
    Location:
    PBG
    is it clutch or flywheel related. try adjusting tension and listen for changes related to pedal travel

    Sent from my SM-G930V using Tapatalk
     
  12. Lawman67

    Lawman67 New Member

    Messages:
    6
    Joined:
    Aug 4, 2019
    Location:
    Iowa
    I will give this a try tomorrow...The battery was too low to crank it over tonight. It's stored at an airport, so it would be easy to pull the filter and pull the paper to see what's in it.

    I can sure check it but I don't recall noticing anything at all when clutching and moving the vehicle around
    I don't notice any change at all in pitch or noise level whether the clutch is in or out or even partially in or out
     
  13. Lawman67

    Lawman67 New Member

    Messages:
    6
    Joined:
    Aug 4, 2019
    Location:
    Iowa
    Well after a couple of trips back-and-forth to the cobra... I wasn't having much luck shutting down cylinders or using a stethoscope so I started pulling a coil boots and found a small amount of oil at the top of the boot on the number 8 cylinder. No more than a 1/2 a teaspoon but best I can tell it got in there from the top side of the head/valve cover. Decided to buy a Harbor freight borescope camera. When I pulled the spark plug the piston is still in there and definitely full of fresh tiny pockmarks so guessing pretty firmly number 8 cylinder piston to valve.
     
  14. Lawman67

    Lawman67 New Member

    Messages:
    6
    Joined:
    Aug 4, 2019
    Location:
    Iowa
    Tried the stethoscope but seemed to make the same noise no matter which side, angle or point i tried. It was worth a try and a lot less than the camera route.
     

Share This Page