Can you tell what's causing this engine noise? I'm puzzled.

[Mike681]

Update in Post Below: Hey guys, I posted on here a month or so ago needing some help diagnosing a noise that I thought was coming from my KB 2.2L. After having KB rebuild the supercharger, the noise is still there and obviously coming from my engine. My car has been at the shop for over a month now, and the guys "aren't 100% sure it's rod knock" and that it could be piston slap, neither of which are good, but they feel it is coming from lower engine. Today they are doing leakdown and compression tests, so hopefully that will tell us something.

That said, with listening to this video, what do you think is causing the sound? Of the dozens of rod knock and piston slap videos I have watched, my noise sounds like NONE of them. Notice that the noise comes and goes and is not constant. Also, turning the volume down on the video some helps clear out some of the surrounding engine noise.

My Cobra has custom fit Diamond pistons, Manley rods, and is bored .30 over.

Now for the video (sorry for the poor visibility as I was in my apartment's garage):

Cobra Noise - YouTube

 

[03mustang92]

Take belt of sc and see if it still makes that same noise, if it doesn't, its the s/c yet if it does...well we got more diagnosing

 

[Mike681]

Sorry, I forgot to mention that the shop did run the engine without the belt and the noise is still there. What gives.

Such a difference between my noise and this cobra's rod knock, for example:

03 cobra knocking - YouTube

 

[Mike681]

Just heard back from the shop, here are the results of the compression and leak down tests. The back two cylinders don't have the best leak down results but overall compression was good. Hmm


1: 180psi 12%
2: 180psi 15%
3: 180psi 20%
4: 165psi 30%
5: 165psi 15%
6: 170psi 20%
7: 170psi 15%
8: 175psi 30%

 

[Jefe]

The intermittent tapping sound? Weird. Anything hitting the fan blades?

Have you pinpointed the location of the sound in the motor? What area? Heads? Up front? Driver side, etc?

 

[Mike681]

The fan is clear of any obstacles, and the shop first thought it was in the lower engine, but now feel it could be some of the pistons, prob 4 and 8. They are going to attempt further diag on Monday. Based on my research it seems like it could be a valve guide, not sure tho. Everyone's sound is constant that has it, not intermittent...maybe my noise was caught early?

 

[SNK-BITE]

Pull the valve covers!!! Thats not a rod knock. There been two threads in the last month on people having rockers poping off. You might have one laying in there hitting/binding with another one.

 

[Mike681]

Yeah I believe I've read those, and that totally makes sense! I'd rather have that problem than rod knock.

This is probably a dumb question, but could that in any way have an effect on the leak down? In looking at my percentages, I'll prob have to have the thing rebuilt/refreshed anyway, right? :shrug:

 

[SNK-BITE]

It would affect it if said rocker caused a valve to hang open but that would be obvious on compression check.

 

[Mike681]

Haha damn, true. This'll be another fun month of my car being in the shop. From a visit that initially was going to be for a tune is likely to turn into a rebuild. It's been in the shop longer than I got to drive it lol.

 

[Mike681]

So my shop emailed me today with this news and remedy to the situation:

"Hey Mike we got to a quiet area to listen to the 2 main cylinders that are low. It’s below past the rings into the crankcase. It’s definite the pistons are loose by the noise it’s making. You do have decent compression so the car is driveable, but it’s not the best way to keep it. Since the car is already bored .030 over or more since it was redone, my guess would be it wasn’t done correctly or it was beaten hard to do this. I would suggest a fresh block because of the issue."

So my big questions are:

1. Do you guys feel that I could and/or should continue driving this car the way it is? I don't exactly have a ton of money sitting around.
2. Should I spend another several thousand dollars for a new block? I've already spent quite a bit so far with everything else I've had done.
3. What are my other choices, if any? (aside from selling the thing)

I've already got 30% leakdown on two of my cylinders, so might it be better to bite the bullet and have everything redone? As opposed to risking it and having everything blow up down the road.

Thanks in advance.

 

[VNMUS03]

Idk... I've heard piston slap is fairly common with forged motors.