Cant keep pinion gear on the motor shaft

[D-DUB]

Kraton 6S BLX.

From the factory the pinion came loose, the grub screw backed out, and chewed up my motor mount a little. No threadlock on the grub screw that I could see. I noticed it after breaking a diff cup. The C clip kept the gear on the shaft luckily.

I've since gone through the entire thing, replaced with EXB diffs, silicone earplugs in the center diff. M2C towers and shock mounts, etc.

I took it out for the first run, and the pinion gear came off again, within the first 10 minutes of running across a grassy field... Not only did the grub screw back out (with blue loctite), but it also sheared off the C clip, welded the aluminum to the grub screw and royally chewed up my motor mount.

What can I do to keep this from happening again? Red loctite the grub screw?

I have a heatsink and fans on my motor.

Any ideas are appreciated.

 

[TexAg09]

How long did you let the loctite cure?

 

[D-DUB]

How long did you let the loctite cure?

Its been about a week. I even made sure to clean it really well before I Loctite it. Brand new tube of Loctite, used brake clean on the new grub screw, and gear before I Loctite it. I have had to take a few things apart that I've used this tube of Loctite on, and its working fine for everything else.
I was really surprised to see this time that it sheared off the C clip, there was still a sliver of it in the motor shaft when I inspected it...

Ill use a snap ring to replace it, since it should provide more surface if this happens again.

Any recommendations on what size pinion tooth count to replace this with? Its a basher.

 

[TexAg09]

Its been about a week. I even made sure to clean it really well before I Loctite it. Brand new tube of Loctite, used brake clean on the new grub screw, and gear before I Loctite it. I have had to take a few things apart that I've used this tube of Loctite on, and its working fine for everything else.
I was really surprised to see this time that it sheared off the C clip, there was still a sliver of it in the motor shaft when I inspected it...

Ill use a snap ring to replace it, since it should provide more surface if this happens again.

Any recommendations on what size pinion tooth count to replace this with? Its a basher.

Oh wow. Think the motor got hot enough to cause the loctite to fail? As far as pinion goes, I'm not sure as I'm running a 24T on an 8S system in my K6S.

 

[D-DUB]

That is the only thing I can think as well, but I just put a heatsink and fans on, its 40F outside, and I was running in wet grass for less than 10min set at 50% throttle on the remote.

I don't have plans to swap around pinions, so ill just use red loctite this time, and if I need to, I can always pull the motor easy enough and heat it with my iron to get it out. I see they also sell some pinions with two set screws. Maybe ill do that.

Just baffles me that this happened two times in a row. Maybe the pinion grub screw threads were cut too big?

 

[Prowler666]

If you keep having this problem look into getting some "Bearing fit" it's a little like TL but you put it on the shaft rather than the thread, It works on rotational forces really well but can still be pulled off when required to change pinion etc.
https://www.bearings-online.co.uk/i...9zA8fmui2mbwmAY_WlUwrxuc-eRS6hOUaAjlwEALw_wcB

 

[Monster Dork]

I do like to use some of the other anaerobic sealants off-label.

It is possible that the threaded hole in your pinion is out of tolerance. Try another grub screw to see if you can obtain a better fit.

You could also try dragging a hand file once or twice over the contact tip of the grub screw to give the metal a better profile for grip against the flat on the shaft.

Another technique is called "staking". After installing the grub screw, back up the pinion on a block. Then use a punch and hammer to dimple the metal surrounding the grub screw. Look it up to see photographic examples. Pretty easy to do.

 

[D-DUB]

If you keep having this problem look into getting some "Bearing fit" it's a little like TL but you put it on the shaft rather than the thread, It works on rotational forces really well but can still be pulled off when required to change pinion etc.
https://www.bearings-online.co.uk/i...9zA8fmui2mbwmAY_WlUwrxuc-eRS6hOUaAjlwEALw_wcB
View attachment 144136

Thanks. Its really loose on the shaft. I'm going to buy a few different pinions to try out.

I do like to use some of the other anaerobic sealants off-label.

It is possible that the threaded hole in your pinion is out of tolerance. Try another grub screw to see if you can obtain a better fit.

You could also try dragging a hand file once or twice over the contact tip of the grub screw to give the metal a better profile for grip against the flat on the shaft.

Another technique is called "staking". After installing the grub screw, back up the pinion on a block. Then use a punch and hammer to dimple the metal surrounding the grub screw. Look it up to see photographic examples. Pretty easy to do.

All great ideas! Thanks.

I think with a better fitting gear, I shouldn't have as much worry of it coming loose. As it sits, my gear without grub screw has about 1/4" of play on the shaft where i believe there should be less than 1/8 to no play.

I actually think that's the cause of my previous issue with this thing, as the screw came loose and the backward and forward slop on the pinion hammered things and caused the diff output to shear off.