View Full Version : Loose pinion grub screws

10-19-2011, 07:23 PM
Just a heads up to X5 owners to check out your pinion for loose grub screws. I had loctited (loctite 243 blue) the grub screws in the pinion during the initial build, and after 30 -50 flights (dont really know the true number) I noticed some red dust from the main gear. Further inspection revealed that the pinion grub screws had loosened (most likley from the motor heat - expansion/contraction), causing the pinion to rock back and forawards on the shaft keys. Yyou can tell if you have this problem by holding the motor in one hand and rocking the main gear with the other whilst watching the pinion. The pinion should not move relative to the motor.

solution : applied permatex bearing mount adhesive to the shaft and pinion and then used loctite 243 on the grub screws again. 20-30 flights later, the pinion is still rock solid. :thumbup:

10-19-2011, 07:30 PM
The main gear should not rock back and fourth either.

Mine doesn't, but my original kits was bad, and empire replaced it.

10-19-2011, 07:38 PM
You should have some freeplay in the main gear to pinion (mesh), otherwise the mesh is too tight and your laterally loading the main shaft and motor bearings, which will cause them to become "rough" quickly. You can't eliminate all play as the main gear is not a perfect circle and there will always be tight spots.

OR do you mean the main gear rocking in the one way beaing hub?

12-15-2014, 05:06 AM

I found this thread and it's exactly what it happened to me yesterday when I was flying my X5 for the 5th time during INVERTED FLIGHT !!

Take-off in normal mode (ESC governor 0-100% throttle curve), then switched to Idle1 (ESC governor, 70% flat throttle curve), doing some translations, loops, all was OK.
I decided to switch to idle 2 (ESC governor, 80% flat throttle curve), I heard motor speed increasing to the new throttle value.
Then I started a loop at 15 meters height, at the top of the loop (helicopter in inverted flight), all the helicopter wagged suddently and the rotor speed decreased.
Immediately I switched to throttle hold, turned over the helicopter and performed a "good" autorotation without any damage, aoutch!!! :peace
At first I thought my BEC has failure and didn't want suply servos but on the ground I noticed some red dust from the main gear and the upper part of the main gear was stripped.
As you can see in the photo, the motor pinion grub screws had loosened causing the pinion moving up closed to the motor.
Does this issue happened to someone and how did you fix it?
I have never seen that, the two M3 pinion screws were well tightened with loctite.
IMO it's due to a lot of motor torque during acceleration from normal to idle1 mode and mostly from idle1 (70% throttle) to idle2 mode (80% throttle).

Thank's for your help.

12-17-2014, 04:22 AM
I took the pinion off and I noticed that the grub screws were not well tightned or lost due to vibration.
Loctite did not worked as I expected, maybe I didn't clean enought the threads, I don't know.

I also have a question about the pinion position, How do you place your pinion (vertical position) relatively to the main gear?
The pinion is not as thick as the main gear so I placed my pinion in contact of the upper part of the main gear teeth, not centered on the gear teeth. Is it a problem?

Thank's guys

12-17-2014, 11:34 AM
My pinion came loose a month ago and luckily I noticed it before flying. It was slipping up and down but would still rotate with the motor. I took the motor mount off and used a new set screw with red loctite and really tightened it down.

As far as pinion position with the main gear, I have my pinion seated as far down on my stock scorpion motor shaft as it will allow. This puts the top of the pinion aligned with the bottom of the main gear.

My main gear has been wobbly for a couple months. My OWB is pretty new and I even added an extra shim between the main gear and auto gear. It is flying just fine so I gave up on getting rid of the wobble. Maybe I'll get a new OWB this winter.

12-17-2014, 11:39 AM
I haven't inspected mine since I built the heli about a year ago, so I guess it's about time to do that. Thanks for the reminder.

12-17-2014, 02:29 PM
As far as pinion position with the main gear, I have my pinion seated as far down on my stock scorpion motor shaft as it will allow. This puts the top of the pinion aligned with the bottom of the main gear.

Why do you place your pinion as far as possible from the motor?
If I understand you placed your pinion aligned with the bottom of the gear?

I would place the pinion centered with the main gear.


12-17-2014, 06:41 PM
I can't remember why I mounted the pinion flush with the bottom of the main gear. Maybe I read it in a build thread or that's what I do with my other heli that has a helical main gear and pinion.

I don't think it really matters to tell you the truth except for maybe the motor shaft won't flex as much.

Here's a pic.