Topic: Catastrophic noise, Help diagnose

[boogiedude]

So I've been trying to diagnose a lean condition on one cylinder and general poor running which I think is related to it, and while I was doing a test run this noise showed up at the top end of the rpm range, and decided to stick around. 

I put a screw driver "stethoscope" on the engine, and it sounds like its in the top end. The cylinder head cover seems to be concealing it. It's pretty clearly a single TACK with each revolution of the motor. My first fear was a spun bearing, but that seems unlikely since it appears to be in the top end(fingers crossed). My other two guesses are a broken valve, or blown exhaust gasket. The noise stays constant all the way up and down even though the video couldn't pick it up when the motor was revved up. It is LOUD.

I can't seem to get it to embed, so heres the direct link while I upload it to youtube

http://www.flickr.com/photos/60875923@N05/8598761095/#secret55a0392fa1




Why me....

[phil71]

Sounds a lot like air escaping. Have you taken compression?

[boogiedude]

not yet, I don't have a compression tester so I'll have to borrow one tomorrow as part of the diagnosis trial. Keep in mind, the noise is much quieter in the video than in person. My phone was being overwhelmed by the exhaust note and sacrificed the tack volume. Also, it is very crisp and defined. It's a bit fuzzy on here... I'll try and get a better sample

[phil71]

I get that, but it doesn't sound metallic. Besides, if you did break something up there, you'll have a discrepancy in compression. Did you pull the tappet covers?

[boogiedude]

Well, good news! It appears the intake valve on cyl #4 backed out, which caused the god awful noise. Dodged a bullet this time...

[nancy]

Is this a 750???
Assuming so,...can't whip off the head cover - but if it were my problem - I'd want to see/hear better and I'll lift the cover up as best I could - maybe prop it open with careful wood wedges...remove tacho drive from cover..I did this to mine when I was trying to solve an oil leak..managed to prise the cover up enough to see a bit in there. Tank off of course.
Use a good light to illuminate the innards...and run engine to see and hear better - duck under the oil spray. Non-metallic type noise had me wondering about camchain rollers/guide...maybe getting beaten to hell after falling apart? Or tacho drive collapse? I'm only guessing. Maybe a valve though....u could turn the motor over manually and try to observe valve operation through the tappet holes?
Mark

[nancy]

Oops - beaten to it..good one Boogie..