I'm starting to think this is not the problem
 

Wear on the front of the starter ring gear, at first I thought this was an obvious sign. Now I'm thinking it's just normal wear from the starter engaging.



Wear on the bellhousing, the only significant area of it. Or is it from me fumbling to get the gearbox on last time and this area was scratched up against the dowel that's fitted next to it.


The area where that wear is located


A continuous area of shiny metal right on the very lip of the bellhousing itself. It's hard to make out and I'm starting to think that I'm poking at shadows.


I'm starting to have doubts about this being the cause of the noise. If it is making contact around the full circumference of the flywheel then I suppose it might be capable of being that loud. The area scratched up near the starter motor housing is so shallow it can barely be felt running a feeler gauge over it. Yet the noise seems to be located primarily in that exact area of the bellhousing.

I'd love to have a smoking gun of metal shavings inside the bellhousing, if there is it's so finely ground it's blended into the clutch dust.

Where to from here?
 
The original plan was to refit the trans without the clutch and run the engine to see if the noise is still there. That'll narrow down the causes.
 
But if it is the flywheel expanding and rubbing against the bellhousing, this is the only cause that fits perfectly with the symptoms, then I'll file down the bellhousing and chuck it back in.
 
The problem is I'm not totally convinced by the evidence I've seen of the flywheel rubbing.
 
I wish I could figure a way to start the engine without refitting the trans!

Jst a quick note, the flywheel has that beveled edge on it as standard, to help teh starter motor engage cleanly and to prevent it binding. I'm still all for putting the box on with only the flywheel installed to see if it's something to do with that pressure plate.

Yeah that's what it's looking like it's going to be

Any change when you ran it without starter motor? Is there any change in sound when you depress the pedal and does the sound speed up in time with increase in revs?

No change without starter
 
A very slight change of pitch when the clutch is depressed
 
Yes it does

Well I can rule out the clutch
 
Damnit!
 
Looks like I need to hunt down something internal to the engine. In which case I have to question the condition of the rest of the internals...
 
Time to rebuild.
 
****it

Damn, only 100k on that engine too?

So I was told

Hrrmmmm...
so it begins again.