strange engine noise cylinder # 6, help !

[jmrc]

Hi Everyone
I having a frustrating issue with my 911SC, (1978) there is a strange noise coming from cylinder # 6
I have to mention that this engine starts and fires normally and idles good there is no blue smoke coming from the tail pipe / exhaust,
I dropped the engine to check on the valve springs I thought that one was probably broken, but after removing the rocker arms, valve springs and inspecting both intake and exhaust I did not find any broken parts and also I remove the chain cover and everything seems to be normal
This is the point where I don’t have any more ideas of what can be causing this noise / problem
Did anyone here had this engine problem before? any comments or advise ?
Video of engine running: https://www.youtube.com/watch?v=XvU51eXJhiE
Thanks
JM

[Flojo]

strange indeed...
maybe a broken air duct tin?
if it does not sit tight in place anymore it might wiggle free and "rattle" when rev is more up giving it the vibration(?)

[Bill Douglas]

An easy thing to check; does the engine have the air pump to the exhaust ports piping still. Has this any holes. And if it has been removed are the plugs (studs) screwed in securely. I ask this because my '79 engine had some bad sounds and was relieved to find it was an easy fix.

Most of all good luck.

[proporsche]

Hi..as Bill said the plugs is loose or you have an exhaust gasket leak...looks like a simple fix

Ivan
you might have a different kind

[Flojo]

oh, I haven't seen these drilled plugs yet. cool detail.

[jmrc]

thanks for all the comments guys

this engine does not have an air pump, I did checked the cylinder head plugs and they are sealed no exhaust leak for what I can see.,

I will check the air duct tin, This afternoon

[jmrc]

BTW, I did check the cylinder head studs and they are Ok

[Bob Kontak]

Just thinking out loud...Make sure spark plug is tight.

[T77911S]

check the oil spray bar for blockage.
had one sound like what I think I am hearing. same cylinder. also sounded funny with all plugs out and engine turning over. (compression test). eventually the bar for #6 intake plugged and scored the cam and rocker. maybe coincidence but after I did not hear that noise.

check exhaust bolts.

engine sounds really good. nice exhaust. maybe noted very slight miss, but I am very sensitive to that stuff.