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407 Oil Cooler Shaft Bearings

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Well here's the results...they changed the hydraulic pump...I ran it up and with my fellow pilot sitting as passenger we went for a short test flight...had no noise or vibs so I land..he gets out and I am heading to YSJ...I do a right pedal clearing turn and the noise is back with a vengeance...and then I remembered this same noise from last year when I was spraying and how I got rid of it was wiggling the pedals back and forth for a second..so I did and noise and vibe decreased a bit..got back to the hangar and keep it running while I had one of our engineers go and stand with hand on airframe back were the servo is...vibration from ****...shut it down and the noise was so loud on coast down that I was sure the engine had not shut off...hit the hydraulic off switch and NO noise...switched it back on...NO noise...they put a portable hydraulic unit on it this morning and I was wiggling pedals with nothing happening until I got back there and had a look...grabbed the push pull linkage and you could get all kinds of slop happening in the servo...then the chief engineer got in and gave it a wrap...well I will tell you it went into a rapid buzz that sounded like someone with a rivet gun going at stainless steel rivets...to stop it he just put his fingers on the pivet bolt linkage...we need a new tailrotor servo...they hauled it out after the bell rep got to hear what it sounded like..will be passing the info up the food chain... :rolleyes:

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Good to hear you found the snag. Your explanation of the snag is almost word for word the same as the guys here described.

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It's great to see questions asked, talked about, and solved. What a novel use for a forum! The maintenance thread is the only thread worth it's megabytes in my opinion. Not like the gigantic episode of Degrassi Junior High that General Helicopter Ops is.

 

Thanks for posting some great helpful info for everyone.

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Hey all,

worked on 407's for 6 - 7 yrs and have only changed t/r short shaft bearings when it was required due to asb and ad's. The one thing bell states is not to overgrease the bearing as it can lead to overheating so I stuck to that premise, also as others have said balance is def important. In my experience it was worth while to use a acid brush and clean out the excess grease to prevent it from being sucked into blower weight assy, where dirt can build up etc. Although the front bearing is a bugger to get at (put a small bend near the end) and try to swab out the excess between the lock ring as well as the shield.

 

Also if you take your time when installing the shaft ,ensure you have centered the bearings as you are torquing the links to prevent any axial loading that can lead to overheating and premature wear. However the machine had no a/c, so I would guess that belt must put a additional side load onto the bearing/shaft.

 

I saw one person had said that he had changed the shaft twice due to corrosion and in my experience the one thing i tried was painting the shaft with a very thin coat of clear. I had no probs with balancing afterwards and corrosion never was a problem.

 

Lastly installing the bearings I have found to be a process you dont want to rush. If you take your time and use dry ice and isopropyl alcohol it makes it super easy to install the bearings onto the shaft, without inducing any stress during the install process. In fact I saw one time once the mixture was poured into the shaft with the bearing just supported in a press, the shaft shrunk so fast that it slipped out of the bearing by itself and fell on to the floor!.... Luckily the foam/rubber that always lives under the press for this very reason saved the day!

There is a large tolerance on these bearings and it seemed to me that even when the bearings are new they feel like they are worn out.... I was told by bell that this excess looseness is built in to prevent overheating.

 

I had heard before about the servo issue people talked about, I never encountered it but thanks for info, much appreciated. Its funny hows it OC isnt it? Its not like its in a place where it gets looked at everyday..... :P

 

Glad to read a post without BS on Vertical as this is the first time I have come on in over a year!

Cheers!

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