[penniesonthedollar]

The noise: Video

I've looked here and elsewhere and havent heard anyone else with this noise. I'm hoping has heard it and determined a cause. It occurs in neutral and appears clutch dependent. It also appears to occur in 1st and only 1st gear.

The engine made this noise occassionaly preceding a rebuild. Engine was rebuilt due to low oil pressure problem. It went down on power and would give low oil pressure warning when hot and ridden hard. There was no obvious cause of the oil pressure problem internally so I replaced both pumps, the over pressure components, seals and gaskets, rings, and other bits, and decked the head and valve cover surfaces to flat.

Motor internals are stock, motorex oil after every track weekend and oem filter every other. It is a track bike so there are a lot of other mods but just not where the noise is coming from, the bottom end of the engine.

-clutch has been checked and rechecked for proper assembly according to ktm repair manual

-pressure plate release bearing has been replaced

-it was unclear if the pressure plate/outermost friction disc should be offset one tooth from the rest of the clutch plates so I've tried both and no difference

-ive found no obvious signs of rubbing or grinding components or worn parts after a thorough inspection of the entire engine.

 

[atinc]

first time i hear duke 390 engine rebuild cause of low oil warning.you sure it wasnt dead oil pressure sensor.
its hard to determine the origin of the noise from da video.could be anything.there are some gears,spinning rotors that are connected,some of them would be stuck.maybe have checked flywheel gear

 

[DukeofSeven]

Interesting. Ok, maybe think about it like this:

If the problem (er, noise) actually occurs when the clutch is engaged and driving the mainshaft, but not when tension is placed on the clutch cable, it is most likely not related to the release bearing, it is more likely a mainshaft bearing/race problem.

It is most notable to me that the problem [completely disappears] as soon as you place just a modicum of tension on the clutch cable...
And the funny thing about that is, the clutch release bearing actually pulls outward on the mainshaft when the cable is tensioned...
So is it possible it is nothing more than the bearing that supports the mainshaft directly behind the clutch, or on the opposite end of that shaft (meaning the left end)?

The reason I favor that at the moment is because you did not actually disengage the clutch, you barely tensioned the cable (meaning you pulled the mainshaft toward the right side of the engine, possibly moving the balls in a worn bearing away from the side of the race that is damaged).

Of course, you're in charge of the stethoscope on this one, I can't really reach it from here. 😁

Please keep us all up to speed on what you find out.

There is one other possibility, however, I need to go back and refresh my memory on something. If it looks like it is something viable, I will post back again.

 

[DukeofSeven]

Nah.. the other thing i was thinking about doesn't actually pan out, on reinspection.

Here are two pics of the right half of the case -- one from directly behind the clutch assembly (if it was removed from the shaft), and one from inside of the right case half (also showing the bearing is retained from within via side plate):

Hopefully it will make more sense now, at least in representation of what I was suggesting before (as a possibility).

Of course, if the noise actually did isolate to that shaft, it could also be emanating from the left-side mainshaft case bearing.
Quite frankly, with all the parts spinning around in such a locality, I never believe I've actually identified the problem until i hold the smoking gun in my hand, away/apart from everything else it meshes with.

 

[penniesonthedollar]

Alright, I like the way you're thinking Duke. Good analysis. My suspicion with the pressure plate bearing was that it was dancing/shaking around and then quieted when the clutch rod made contact. Nonetheless, it's been replaced and the noise persists.

I tried running the bike listening specifically with the mainshaft bearings in mind. But, the bike wouldn't make the noise and this bike is too loud to run in my garage all day having neighbors. I'll try again each day until I can get it to make noise.