immediately after an unnecessary and unmatched downshift on track (but probably not an over-rev technically speaking - judging by a video which doesn't show revs going above 8500) i got extremely loud ticking which is synchronized with engine speed. i pulled over and shut the engine off. had the car towed home. no check-engine light. car is drivable and idles fine (based on another minute of running i was able to bear).
the ticking sounded valve related, especially remembering all the stories about broken rockers and warn camshafts (a related link listed here), so i took the valve cover off the other day.
as these 5 pictures here show (the remaining 3 look similar), everything looks good under there to me: no wear on camshafts that i can see, all the rocker arms are in one piece.
i was able to rotate the engine to take a look on all sides of the camshaft, by turning one of the rear wheels (spark plugs out, trans in first). a slightly strange thing was that difficulty in turning was not smooth - i would struggle, than there would be a burst of easy motion, than struggle again, and so on. maybe that makes sense with the different pumping resistance from the engine at different parts of the cycle; maybe.
but then the truly strange thing was that after some point i could not turn the engine anymore this way, no matter how hard i tried. it seemed like something was blocking it at that point.
my theory is that i have one or more bent valves which are not moving properly anymore and are hitting the piston. this would be creating the ticking noise. and in my turning by hand i might have reached this interference point so that i can't turn it by hand anymore.
based on that, i should take the head off and inspect the valves and tops of pistons.
my questions are:
- any better theories?
- is what i have described worth the pain of removing the head to see what is actually going on?
- if so, could somebody point me to any discussions related to that work that would be a good supplement to the toyota engine manual?
- anything else i should be looking into here to diagnose this?