Originally Posted by Diseasel300

Unless you have serious chain stretch from extreme lack of maintenance, IP timing and base engine timing are the least likely to be your issue here. 60x engines just don't eat chains like the 61x engines do and there's no offset keys to adjust cam timing either. I've serviced 603's with 300-400K on them and the original chain with 1-2˚ of stretch and left them well enough alone.

I would have hoped that my previous reply about the delivery valve leaking would have been heeded, but nobody ever listens to someone with experience, so why am I not surprised? There's a reason I rarely contribute to this forum anymore. The injector isn't the issue, it's delayed or improper combustion. I've dealt with many 60x engines with this noise and DV's generally improve or eliminate the issue. Newly rebuilt injectors shimmed to the correct pop pressure always seem to exacerbate a leaking DV compared to an older worn/weak injector. The older engines with the "vertical" injection prechambers are far noisier and always have a certain degree of a metallic "cackle" at idle. Some degree of knock is to be expected and has to be tolerated.

In this case, you have a combustion problem, likely a leaky DV or worn DV seat. Air in the return lines is normal. You don't normally see it with the black/grey rubber ones and it takes a LONG time for it to work its way out. The leakage through the return/leak ports in a well-lapped injector is very small, so the flow through those lines is minuscule.