Front transmission noisy

[MadBird]

Hey guys I have a rattly front transmission on the N7 when the heli unloads after a collective input. ie If I input collective and climb straight up and then go to neutral collective it will be noisy until the drive train loads up again.

I haven't taken the transmission out yet to check whats going on as I will putting in a few flights tomorrow however I thought I would put up a quick post in here to see if anyone has had a similar experience and see what their diagnosis was.

I have had a quick play on the bench and it is definitely the front transmission. The grub screw and lock nut are both very snug also.

Thanks, Matt   

[Ross Lawton]

Hi Matt,

Check the front bevel gears for any wear, if the gears have excessive wear on them this could lead to a slight amount of gear chatter.

Can you see how far the boom assembly is installed into the main boom clamps of the main mechanics? The end of the boom should be flush with the front edge of the front boom clamp. This will allow correct distance and also make sure that no pressure is exerted onto the torque tube, what i have seen happen in cases where the boom has been pushed past the front boom clamp during assembly is that the pressure excerted on the bevel gear can push it forward slightly so that it effectivly tighten's the mesh and causes a noisy gear train which will in turn cause excessive wear on the gears.

It is something i have noticed and may be worth checking, if you do find that the boom is not flush with the front boom clamp edge then i would reset it and replace both the front bevel gears.

Hope this helps, let me know how you go and if i can be of any more help just give me a shout. 
Cheers,
Ross

[MadBird]

Hi Matt,

Check the front bevel gears for any wear, if the gears have excessive wear on them this could lead to a slight amount of gear chatter.

Can you see how far the boom assembly is installed into the main boom clamps of the main mechanics? The end of the boom should be flush with the front edge of the front boom clamp. This will allow correct distance and also make sure that no pressure is exerted onto the torque tube, what i have seen happen in cases where the boom has been pushed past the front boom clamp during assembly is that the pressure excerted on the bevel gear can push it forward slightly so that it effectivly tighten's the mesh and causes a noisy gear train which will in turn cause excessive wear on the gears.

It is something i have noticed and may be worth checking, if you do find that the boom is not flush with the front boom clamp edge then i would reset it and replace both the front bevel gears.

Hope this helps, let me know how you go and if i can be of any more help just give me a shout. 
Cheers,
Ross

Hey Ross thanks for the reply mate. I have just replaced the front bevel gears due to a tail blade vs terra firma incident and the boom is indeed mounted flush with the front boom clamp, so there shouldn't be any issues there. The the old bevel gears weren't worn at all with only 45 or so flights on them and the new ones displayed the same symptoms right off the bat.

After some investigation I think that I may have found the source of the noise however I need to do some more testing to be sure. It looks as though the torque tube bearings are a little notchy and when the load comes of the tail it causes the rattling noise to reverberate through the boom/tt and into the transmission. Seems weird I know, but that's what I'm seeing so far.

My next move is to quickly swap the boom off my E7se and spin the drive train by hand and see what I can here. If the rattle disappears then I'll be on the right track and will be confident that replacing the bearings on the N7 torque tube will do the job.

I'll let you know how I go.

Thanks again, Matt

[Drew Robinson]

Nice part about having e7/n7 combo I have swapped heads to rule out issues before!