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HelicopterEngines Plugs Mufflers Fuel › C-Spec Mystery... Any Ideas?
09-02-2003 01:34 AM  14 years agoPost 1
Zapped

rrNovice

Pensacola, Florida

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I have an OS91 C-Spec with an MPII muffler. The engine has a header tank and runs on muffler pressure. It has run like a champ until today and has over five gallons thru it. It has never been run anywhere close to lean.

Today from close to the ground I did a hover to full throttle climb out with a roll in the middle. At the top of the climb out, the motor went crazy. It sounded as if throttle was going up and down rapidly. I immediately suspected GV-1 had thrown magnet or broken sensor. Brought the heli down in one piece.

First check GV-1. Everything was fine. Magnets alright sensor picking up signal fine. Then checked all obvious fuel line problems. Couldn't find anything in the field.

I changed the plug and fired it up. It idles fine. When powered up past half throttle, with or without governor, the power comes and goes.

Anyone have any ideas? I will replace all fuel lines and filters to see if that helps.

Phil

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09-02-2003 02:05 AM  14 years agoPost 2
Govanator

rrApprentice

Dickinson, Texas

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C-Spec

Do you have a perry pump installed. If so cheeck your line that goes to the crank case and make sure it has not cracked. Also check your fuel filter and make sure its not plugged. Last thing is bypass the GV-1.

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09-02-2003 02:08 AM  14 years agoPost 3
Zapped

rrNovice

Pensacola, Florida

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No pump. I wished I had thought of bypassing GV-1 module at field.

Thanks

Phil

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09-02-2003 02:25 AM  14 years agoPost 4
irq

rrKey Veteran

San Diego, CA

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Which helicopter do you have this engine in? Check your auto bearing.

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09-02-2003 02:31 AM  14 years agoPost 5
DOKEY

rrProfessor

Northamptonshire UK

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Not sure about the combination you are running but i had simular problems with a Throttle Jockey combined with a 8700g servo.

Seems the 8700g wasnt compatable, just went crazy, changed to a 591 servo and problem solved.


Ryan.

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09-02-2003 02:43 AM  14 years agoPost 6
Zapped

rrNovice

Pensacola, Florida

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irq

Funny you should mention auto bearing. The one way bearing that releases the main gear and clutch bell from driven tail has been sticking for the last two gallons.

Do you think the main shaft is not being driven? Do you think the full power climb out may have further damaged the autobearing? Please give me your thoughts.

I did turn off GV-1 at field. The problem was still there. The servo is a 9202 and has worked flawlessly.

The heicopter is a Predator.

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09-02-2003 02:46 AM  14 years agoPost 7
irq

rrKey Veteran

San Diego, CA

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I am completely unfamiliar with the Predetor design but I know there are one way bearings in the drivetrain somewhere, and this problem sounds exactly like a one-way bearing problem. If I were you, I would not continue to fly this ship at all until you check those bearings and replace them. Really, the best way to find out if they are bad is to replace them and see if the problem goes away, as they can be damaged in non-obvious ways. All you need is for that bearing to give out completely....

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09-02-2003 03:54 AM  14 years agoPost 8
Zapped

rrNovice

Pensacola, Florida

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Nothing like a surprise auto, huh?

It is safe to say that this ship will not leave the ground until the problem is found and solved.

The predator is a great machine so far with super inexpensive parts supply. That auto hub is, however, $125.00.

Phil

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09-02-2003 03:57 AM  14 years agoPost 9
irq

rrKey Veteran

San Diego, CA

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Well hopefully you don't need to replace the auto hub, just the bearing... but again I'm not familiar with this ship so I don't know if that's possible. I'm sure MG/Lift/someone else will chime in.

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09-02-2003 04:12 AM  14 years agoPost 10
Zapped

rrNovice

Pensacola, Florida

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I am not sure how the auto hub goes together, but I will be tearing it down tommorrow to find out. The instructions are pretty weak on the auto hub as it comes assembled. I went back and looked at parts list and it implies there are two parts to the drive. It does not show them, however.

Phil

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09-03-2003 05:19 AM  14 years agoPost 11
jkelly

rrVeteran

Bedford, PA

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...sure does sound like the 1-way bearing. When mine went in my Freya it did something similar to what you described. My bearing case cracked and it would allow the rollers to spread apart too far allowing the shaft to slip causing the engine to rev. It was difficult to tell by just rotating it by hand as the hub holds it tight but under torque it can slip. If that's not it, make sure your plumbing is good. I had a crack that was difficult to see in my pressure line at the muffler nipple once. That was causing it to lean out at random.

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09-03-2003 08:21 PM  14 years agoPost 12
Zapped

rrNovice

Pensacola, Florida

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You guys are good. I disassenbled the drive train and the autohub is clearly broken as it will turn the wrong way under large force.

I cannot get the unit apart so I cannot say for sure what failed.

Got a new one on the way.

Phil

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HelicopterEngines Plugs Mufflers Fuel › C-Spec Mystery... Any Ideas?
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