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OS rear main bearing failure symptom?

flyboy907

Veteran

woodstock, ga

Hey guys need some quick help diagnosing a tail twitch on my 600n.
I have a os50 hyper in it running carbsmart at the 110c setting. I have recently developed a strange tail twitch accompanied by metallic buzzing sound of sorts. It is not as noticable in normal mode but highly noticable in idle 2 which is 2100rpm with atg gov. I am trying to figure out if this may be a rear bearing issue in the motor or if I need to look elswhere. looking directly at the tail in hover in idle 2 the tail will quickly just twitch back and forth with a short little buzzing type noise at the same time as the twitch. lol sound like morse code. I cant figure it out any help or sugestions would be great.

01-30-2009 Over year old.
HOMEPAGE  
Duckster

Senior Heliman

Brunei

One of my friend experiance this thing too but it was happend after a crash, and we found out one of the roller inside the one way bearing inside the clutch worn out (try changing them), and may also cause the clutch to break, and the tail twitching thing u may check the main shaft bearing if it is after crash it may cause it to worn too, and cause a vibration to the whole body and may effect the gyro, its hardly effect the bearing inside the engine(but just check them) in my case , i only change the bearing if the crash is really bad on engine area and about the engine bearing try find and replace a bearing that come with seal cover, u may check by pulling the bearing and and test it with something that u can hold and turn the bearing and if u find the bearing making rattle feel that mean u need to replace it, for one way bearing just check the roller inside the bearing or else just replace it with the new one just cost u few BUCKS and grease it before use. Just an Opinion to make ur bird fly better

Trex 600,700 AND 450, GY611, GY401, OS5H, OS91HZ, MGP, HS65HB, Scorpion 2221-8,

01-30-2009 Over year old.
HOMEPAGE  
dkshema

rrMaster

Cedar Rapids, IA

If you're concerned about the rear bearing being bad, just start the motor and listen to it at idle. With nothing but the motor turning, you shouldn't hear all sorts of odd rattling, clanking, or other noises, just the motor running.

Twitching as you described it might be a slipping one-way clutch, or it could just be a sign that at the rpm you're hovering when you see it, the motor is just a bit on the rich side.

A second common symptom of imminent rear bearing failure is the tendency of your motor to just plain quit suddenly. You re-light it, and as soon as you remove the battery from the plug, it quits. Or it will run up till about 1/4 - 1/3 throttle, then stop dead cold. Replacing the plug may fix this for a flight or two, then it happens again. This is from bits of the bearing actually flaking off and reaching your glow plug which kills the fire instantly.

The metallic buzzing noise doesn't sound promising at all. Might be time to go over the clutch assembly, check out the one-way clutch, and the motor too. A few hour's worth of preventative maintenance may save you a costly and time-consuming rebuild.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

01-31-2009 Over year old.
flyboy907

Veteran

woodstock, ga

thanks for the responses guys, When you say one way are you refering to the one in the main gear? My motor sound good at idle so I guess it probally isnt the rear bearing. I think I will take out the motor and look at the clutch and what not

01-31-2009 Over year old.
HOMEPAGE  
Duckster

Senior Heliman

Brunei

nope the bearing at the clutch

Trex 600,700 AND 450, GY611, GY401, OS5H, OS91HZ, MGP, HS65HB, Scorpion 2221-8,

01-31-2009 Over year old.
HOMEPAGE  
dkshema

rrMaster

Cedar Rapids, IA

The one-way clutch I'm referring to is the one in the main gear that allows the MR shaft to freewheel during autos.

-----
Dave

* Making the World Better -- One Helicopter at a time! *

Team Heliproz

01-31-2009 Over year old.
kcass518

Veteran

Manhasset, NY - USA

How do you test for a 'slipping one-way' main bearing? I took my main gear out, put the jesus bolt back in the bottom hole and am turning the gear forwards and then back and it doesn't seem to slip at all. But when I'm in the air, everything is fine until I lower my collective to come in for a low approach. The engine seems to disconnect from the drive train, and at the bottom of the approach, it clicks back in. It sounds like I'm shifting gears, but the engine keeps its rpms all the time, limited by the gov. I would suspect the oneway, but my testing tells me it's alright. And it can't be the clutch or it would show symptoms when starting out.

07-10-2009 Over year old.
Duckster

Senior Heliman

Brunei

my experience on one way bearing problem on the main shaft is, firstly where i try to spin the main gear it was abit sticky, and secondly when i flew my heli and landed i try to check the main gear the main gear stuck (i turn the main gear both way my blade are spinning) i check out on the one way it should be one of the bearing sticking out or not balance no more and i blew it with air compressor one of the bearing flew out from its position supposed to be what i mean hear is the bearing in cylindrical shape in where i dont know the name i use to call it rod bearing hehehe ...

anyway just try change a new bearing it wont cost u much, just imagine if u need a force landing ie: engine flame out and need an auto rotation on a high altitude u wold loose ur head speed due to drag between ur main gear and tail drive gear and ur heli will fall down like a rock instead it supposed to float in the air b4 it meet the ground and u will spend much rather then rplacing just a broken skid

anyway a good fly and skill is u land ur heli in 1 piece

Trex 600,700 AND 450, GY611, GY401, OS5H, OS91HZ, MGP, HS65HB, Scorpion 2221-8,

07-11-2009 Over year old.
HOMEPAGE  
kcass518

Veteran

Manhasset, NY - USA

Thank you. I switched to another one-way, and that's not my problem. I'll keep looking. OAO

07-11-2009 Over year old.
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OS rear main bearing failure symptom?

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