Engine Noise

[VAroute66]

I have a ZZ502 that was broken in but has never been in a car. I am able to run it in on a test stand. There is a rapping noise that comes from cylinder number 8 best I can tell from the the head. Its hard to tell if its coming from the upper head or the noise is being transmitted from the piston through the cylinder.

- The noise is not present at idle
- It does not change with temperature (Pretty sure not piston slap)
- most prevalent during rapid changes in RPM. If I bring it up slowly, it will not make the noise. Quickly, it will. Backing off can hear but then sounds more like a lifter noise.
- Next test will be to remove coil from that cylinder to see if noise changes and check valve adjustments.

Is rod knock always present at idle even in its early stages.


Any thoughts/advice/condolensces before I start tearing it apart? Thanks for your thoughts.

Route66

 

[Tom Bryant]

That is strange with a new crate motor. Rod knock is usually louder when you run the rpm up and then back of the throttle. The loudest noise will be on the down side. Bad rod knock can be heard at idle too. Rod knock and loose wrist pins sound alot alike. Have you checked for a loose rocker arm yet? Is it still under warranty? Don't do any major disassembly if it's still under warranty.

Tom

 

[tmkassin]

Try running a compression check. If it's low on that cylinder then think cracked piston or dropped valve.

 

[VAroute66]

Tom, tmkassin,

Thanks for the reply. A new shortblock should not have these issues. This one was owned by someone else for about 10 years so warranty resolution is probably not a possibility. I am in the process of checking the valve train and cylinder compression. Thanks again.

Regards
VAroute66