Intermittent, non rhythmic, non directly 1:1 rpm related like a rod (mostly). Seems to be coming from the valve cover, but stethoscope denies and visual inspection showed nothing.
No glitter in oil. But oil was super thin and dark when drai ed tonight.
Im stumped. Can find no external source, can't pinpoint with stethoscope. Unhooked all accessories but alternator and water pump.
Tried a video....
Have you disabled the cylinders one at a time when running?
In reply to Noddaz :
No.
Hadn't thought of that, as it didn't sound cylinder dependent.
And to be clear, the tap sounds in person like a ratchet handle smacking the valve cover. Hopefully its clear enough on video.
Bump for the morning crowd
Its in the belt drive. Removing alternator/waterpump belt it goes away. No smoking gun for why, but i know its not internal.
I meant to reply this morning but had one hell of a busy day.
I was going to suggest alternator so I was sorta kinda in the right realm. The alternator on my NA is olllllldddd and it makes a similar racket at idle sometimes.
If there are any idler pullies, check them first.
I had a horrible knock/gronk sound that sounded for all the world like the rearend was coming apart on my first RX-7. It was the A/C idler pulley!
For whatever reason, idler bearings fail fastest. Maybe they are cheaper in construction, maybe it's because they spin a lot faster.
Check the crank dampener and make sure the crank bolt didn't back out or come loose.
Ok, in the belt drive. You had the belt off, spin the alternator and idler by hand and see what is not turning smoothly.
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