Hey guys I need your help. I was ta the dyno shop today getting the car tuned. It was running well for about 2.5 hours and then it started making a tapping sound from the left/drivers side bank. It was a metalic sound and was pretty fast. It didn't do it at all rpms and didn't do it until it ran for a couple of hours. When I went to trailer the car up after 30 min the sound definietly wasn't as loud. My engine is pretty much stock but with mild cams (about 8.5mm valve lift) and mild head porting. But I need to figure out what this could be so this is what I ask of you.

1) Possible causes that would be making this sound. (The guy at the shop said it may be a valve or rocker or something.)

2) Methods to figure out what is making the sound? Like what should I take apart and what I should look for?

A little history: My car actually had this tapping sound before and eventually that cylinder lost compression so it ran like crap. I sent the car to the factory and this is what the guy had to say. (Keep in mind that this place does really crappy work although he does sound like he knows what he is talking about.) So hopefuly this will help you answer my question. This is what the guy had to say:

The cams run on a hardened steel shim
which is contained within a bucket which also pushes down on the valve. The
bucket is made from aluminium and the shims come in different thicknesses so
you can adjust your clearance correctly.
What had happened was that the shim got a little bit of surface rust on it,
like the brakes did, which meant that what is normally a polished surface
that the cam runs on was now higher in friction. This meant that the cam
grabbed it each time it went by, slowly hammering the side out of the bucket
and eventually spat it out of the bucket. On the way out the shim damaged
the bucket which meant that although the cam pushed it partway down the bore
it runs in, the valve spring wasn't strong enough to push it back up. Hence
that cylinder had no compression as the valve was permanently open. The rest
of the shims showed no signs of any rust. I greased all these before the
engine left to try & prevent this occuring, but it did anyway! This problem
also accounts for the tapping sound the engine had. there are 32 of these
items.

Thanks,

Adam

 

sounds like the injectors doing there job. If you have a 400, it is noticeable.