Noise when rotating blades by hand

[seneca2e]

Okay here's another question. When rotating my rotor blades by hand I hear a very clear noise like a ratchet wrench. It does this in both directions but sounds somewhat different when the sprag clutch engages when I spin it backwards. I used a mechanics stethoscope and it sounds a bit louder when I put it on the transmission housing just in front of where the tail rotor drive shaft goes into the tranny. Does anyone else have a noise when rotating their main rotor blades by hand? I'm not sure but it does not sound like it is in the main clutch or sprag clutch or rotor brake-with the stethoscope I "listened" to these as best I could. Could the noise be gear mesh in the main transmission or tail rotor gear box noise(Bill speculated on this one)?

[bryancobb]

Man!

If you can eliminate the main clutch, Formsprag, rotor brake, rag-coupling and banjos, and forward Morflex (as you seem to have done), then it sounds like it is probably gear teeth.
It is not normal though.

Some ratchets have staccato "clicks" as the handle is turned and some have dull little clunks. I would say the dull type would be what the gear teeth would make if they were badly worn or loose in their engagement, etc.
A clicking could be something as simple as the tip of the rotor brake cable hitting the 3/16 nuts around the perimeter of the big clutch?

When you flip the prop on a piston airplane, the noise from the magnetos is what I mean by clicking.

I don't think I'd fly it until you nailed down the source?

[seneca2e]

Yes I've got to figure this out before flying it. I'm thinking it's gear noise but no way to tell for sure without further troubleshooting. It had a transmission output seal replaced on one of the last annuals.

[seneca2e]

Here are some short clips with audio of the noise. If anyone has heard this noise please chime in or even if you haven't chime in anyway lol. Note two of them are in the normal direction of rotation and one backwards(you can see sprag clutch grease nipple spin by thru access hole in dust cover of main clutch.



http://s135.photobucket.com/albums/q143 ... ynoise.mp4

http://s135.photobucket.com/albums/q143 ... noise2.mp4

http://s135.photobucket.com/albums/q143 ... noise3.mp4

[bryancobb]

That is definitely gear teeth noise. I could be wrong but here's my thoughts.
* Too low in pitch to be the T/R gear meshing with the sun gear UNLESS SHIMMED IN WAY TOO DEEP WITH NO LASH.
* Too rapid to be planets meshing with the outer ring.
* Just about perfect speed for the sun gear meshing with the planets.
* Just about perfect speed for the T/R gear meshing with the sun.
* Constant noise doesn't indicate broken teeth.

There's no way to adjust ANY gear lash in the MRGB except the tail rotor drive gear.
I think THAT is going to be your culprit. I think the shims have came apart that set the T/R drive gear to sun lash.
The tips of 80deg +/- beveled gear teeth on that shaft are hitting the bottom troughs of the beveled T/R drive
portion of the sun gear. It COULD be the planets I suppose if the needle bearings are in bad shape? I can't remember
if the T/R gear lash can be adjusted from the outside or if you must separate the case? If you do, it is pretty simple because
the outer ring gear acts as a locator to align the case halves and there's no way to mess up any adjustments. The only worry
is a little rope seal that wraps around and keeps a leak from happening.

Laminated peel-away aluminum shims are used there if I remember right. I had a hard drive crash 10 yrs ago and I lost the CAD drawing, but here's the only print I have of that drawing. Maybe it has enough detail you can see. I mic'd everything when mine was apart. Picture coming soon. Please be patient.

[seneca2e]

I just pulled the parts book to study what you said Bryan. Very plausible explanation. Plus it just seems to be emanating from that area. Thanks for your input as always!

[bryancobb]

Here's the picture.

[seneca2e]

Bryan that picture is awesome. Nothing in the parts manual even close to the clarity of that! Was that from a transmission overhaul manual(which I've never seen) or did you make it?

[bryancobb]

Thanks for the kind words. Drawing is my "real job."

That was MY AutoCAD creation. Everything I ever disassembled on my helicopter was mic'd and drawn ( I had more time then LOL). This drawing was not taken from any book. I had each part in my hand as I drew them.
I hate it that my hard drive crashed and that file wasn't backed up anywhere. That 1 sheet that I printed is the ONLY one that exists in the world. It was printed to show Ron Froberg how to reassemble my gearbox when he did the 1200hr. I had punch-marked the parts so they went back in the same exact place.

[9121u]

HI ED maybe call BILL M. I think he has a new MR gear box like 100 hrs on it tt .might be better than trying to repair yours if its got a lot of hours on it...just a thought... I no that noise is not normal...

[seneca2e]

Okay Tom good idea actually been talking to Bill and he's really been helpful-actually offered to let me swap the gear boxes to trouble shoot the noise. Just a pretty lengthy trip up there. The transmission was overhauled less than 75 hours ago and I'm pretty sure it's those bevel gears as Bryan surmised.

Bryan that was a shame you lost that info. It would have been an unbelievably helpful supplement to the Brantly manuals! Again great job on the drawings!

[bryancobb]

Thanks again for the kind words Ed,

That gearbox that Mr. Mott has was in this ship when it was rolled over. If you go that route, it would need a "sudden stoppage" inspection.

[bryancobb]

Here's the type shims that Doyle sent me when I overhauled mine. These were placed between the outer races and the case on the two pinion shaft bearings, to set the proper lash. If these aluminum shims have squeezed out the the bevel gears can mesh too deeply!

[seneca2e]

Did you use the 1100 aluminum shims or the stainless?

[bryancobb]

I actually ordered mine fro Brantly. Doyle had them in stock and I wanted a Brantly receipt with them listed, but they were aluminum.