Here's a thought I had about the chains... The rear chain (secondary) seems to have stretched slightly since new, unless this is normal: Without the tensioner in place, the timing marks line up perfectly. With the tensioner in place, they're slightly off. If I line up one mark so that it's even with an imaginary centerline across the two cams, the other cam isn't quite right. I don't have to rotate it a lot, but if I line up either cam, the other one has to be turned slightly to line up (less than a half a tooth, but close). Assuming the front chain is fine (and those timing marks are perfect with the tensioner in place), this would mean that the rear cam is timed perfectly with crankshaft rotation, but the front isn't. I really don't think there is any valve contact, as I don't hear anything through an open spark plug hole. I'm not really sure how, but I wonder whether a slightly mis-timed front cam could result in the sound I'm hearing, which definitely comes from somewhere behind the cam plate (unless there is a SERIOUS aural trick going on...).

Yes, the cams are basically pressed into the front bearings, although each one is located/secured a little bit differently. The front is pressed in and located with a retaining clip, the rear is sandwiched between a little spacer on the inside, and a spacer behind the chain sprocket on the front. I suppose I could try replacing the outer bearing, at least on the front cam, but it really looks correct...

 

I THINK I'VE SOLVED IT!!!!

I kind of ran out of steam for a week or so and got super busy at work, so I stepped away for a little. I did try replacing my unknown-brand pushrods with a set of S&S adjustables (not quickees), on the remote theory that MAYBE the non-spherical ends were causing some slight interference with the rockers that was somehow manifesting itself down at the bottom, but that wasn't it.

So I started thinking again about the fact that my new rear tensioner is already wearing faster than the front, and this had also been the case with the old spring tensioners... What parts are still in common that haven't been replaced? The cam chains. I ordered two new silent chains from Boardtracker.

Last night I took my cam plate back to work to use the hydraulic press, and popped out the cams and outer bearings. I put it all back together with new bearings and the fresh chains. Just spinning the cams in the plate with the inner chain installed, I could feel a difference right away... They spun really smoothly with little noticeable resistance. That wasn't true before. You could easily turn them by hand, but it felt chunky the whole way around. I just mocked it all up in the cam chest with everything just past hand tight, dropped in the front lifters, adjusted the front pushrods, and turned the engine.

No more clicking sound!!! Also, the outer chain now has consistent tension the whole way around and the tensioner no longer pops out suddenly as it did in one of the videos earlier in this thread. Maybe the secondary chain had some tight spots that somehow affected the rotation of the front cam when it was under the most tension, at the high point of each lobe. Somehow this must have caused the lifter to come down the ramp more aggressively than intended, causing a sound as it did so? I dunno... All of the surfaces look fine.

Everything seems to spin freely and quietly now. I just hope that nothing was damaged before I was aware of a problem, as I'm sure it was developing before I realized it. I don't see anything wrong, but...

Now I just have to take it all out again, make sure there's no old dried threadlocker anywhere, put it all back together properly torqued, and reinstall the pipe.

But of course nothing is smooth... In all of the taking things out over and over again, the number one hole for the cam plate bolts seems to have stripped... I have some 1/4-20 helicoils, so I guess that's the first order of business now...

But at least I can see the path to starting it up again!

 

Yay!!

 

Hoping for a continued feeling of relief

 

Nice. Glad to see you got that figured out.