99 With a "Knock" "Tap"

[Lawman67]

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.

 

[PaxtonShelby]

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.

 

[01yellercobra]

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.

 

[wkornf]

I've never heard a rod knock like that. maybe a follower popped off or something. or timing chain is loose.


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[Lawman67]

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.

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.

 

[Lawman67]

I've never heard a rod knock like that. maybe a follower popped off or something. or timing chain is loose.


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Hmmm, worth pulling a valve cover or what would a guy look for?

 

[tharv71]

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?

 

[decipha]

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.

 

[decipha]

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.

 

[bigja01cobra]

get an automotive stethoscope and probe while it is running it should help with narrowing down where the noise is coming from.

 

[wkornf]

is it clutch or flywheel related. try adjusting tension and listen for changes related to pedal travel

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[Lawman67]

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?

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.

is it clutch or flywheel related. try adjusting tension and listen for changes related to pedal travel

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is it clutch or flywheel related. try adjusting tension and listen for changes related to pedal travel

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I can sure check it but I don't recall noticing anything at all when clutching and moving the vehicle around

is it clutch or flywheel related. try adjusting tension and listen for changes related to pedal travel

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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

 

[Lawman67]

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.

 

[Lawman67]

get an automotive stethoscope and probe while it is running it should help with narrowing down where the noise is coming from.

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.