Getting the Pinion to stay on the motor shaft? - RC-Monster Forums

Thirdgen89GTA · **Getting the Pinion to stay on the motor shaft? -** 01.09.2012, 09:14 PM

Anyone have any advice on this "fun" problem? Running 3S or 4S its not a problem. However put 6S on the truck and after about 2-3 minutes of running the pinion will walk itself off the shaft. Thankfully I've been lucky in that each time its done it, it hasn't stripped a spur or pinion. no real wear/tear honestly. Also, my battery tray keeps the pinion mostly on the shaft so it doesn't get lost. An unintended benefit of the way I built the conversion.

I've used globs of blue loctite. Waited 24hrs before it cured. I've replaced the set screw thinking maybe the old one just just not holding.

I've tried with the pinion in both directions.

If I had any red loctite I'd be using that now, but I'll be buying some tomorrow simply because i'm tired of only being able to run 2-3 minutes before having to "fix" the truck.

I had even considering marking where the set screw sits and cutting a tiny indentation in the shaft so the set screw can sit "in" the depression. But I don't want to cut shaft if I don't have to.

If I thought I'd never have to take this motor out of the car ever again I might even JB Weld that thing on there. I just want to play with my new toy, not fix it constantly.

brian015 · 01.09.2012, 09:33 PM

The only time I had trouble with a pinion coming off like that was when my motor mount was misaligned, so the pinion was meshing at a slight angle with the spur. This produced a force on the pinion that pushed it outward toward the end of the motor shaft and it came off regularly, until I fixed the misalignment.

Thirdgen89GTA · 01.09.2012, 09:39 PM

Quote:

Originally Posted by brian015

The only time I had trouble with a pinion coming off like that was when my motor mount was misaligned, so the pinion was meshing at a slight angle with the spur. This produced a force on the pinion that pushed it outward toward the end of the motor shaft and it came off regularly, until I fixed the misalignment.

I'll have to look at that. It didn't look crooked, but i also didn't consider the possibility that it could be crooked. I figured when the motor was tightened down it would flatten itself out as long as something wasn't between the motor and the mount.

brian015 · 01.09.2012, 09:40 PM

Quote:

Originally Posted by Thirdgen89GTA

I'll have to look at that. It didn't look crooked, but i also didn't consider the possibility that it could be crooked. I figured when the motor was tightened down it would flatten itself out as long as something wasn't between the motor and the mount.

In my case, it was the motor mount itself that was misaligned, not the motor to the mount - if that makes sense.

Thirdgen89GTA · 01.09.2012, 09:43 PM

Quote:

Originally Posted by brian015

In my case, it was the motor mount itself that was misaligned, not the motor to the mount - if that makes sense.

I don't think that will be the case for me then. I'm using the factory drilled differential holes. All I did was switch the direction of the diff. So it should be fine.

coolhandcountry · 01.09.2012, 09:54 PM

If you look in your other thread about the build of this truck.
You can see the diff is not lined up with the motor mount end of it.
This could be your problem.

coolhandcountry · 01.09.2012, 09:55 PM

Here is the pic I was refering to
http://gallery.me.com/thirdgen89gta/...13257464680001

Chainsaw10 · 10:05 PM

What I did with my MT4-g3 is dremel a small divot in the motor shaft where the set screw contacts it.... This let's the set screw sit a tad deeper. Red loctite should also work. There are also pinions with two set screws that will do the trick..

Here's one
http://www.ebay.com/itm/NEW-Tekno-R-...6#ht_626wt_698

Thirdgen89GTA · 10:06 PM

That was the test fit with the spacers underneath the differential. Those are gone now because the chassis was clearanced so the spur didn't bottom out.

Here are two new pics from that. It looks like the pinion slipped a bit before I tightened it down in the opposite orientation to the way I had it before. Thats as far back as it will go with the set screw tight. I'll swap it again.

George16 · 10:12 PM

Just grind the set screw flat so it will have a bigger surface area to "grab" into the shaft. I do this on all my set screws and no problems so far.

Thirdgen89GTA · 10:10 PM

Quote:

Originally Posted by George16

Just grind the set screw flat so it will a bigger surface are to "grab" into the shaft. I do this on all my set screws and no problems so far.

I'll try that now before get into doing anything to the shaft. I have plenty of set screws that fit. :)

BTW, the diff looks straight in the 2nd two pics I posted. Can anyone else see any angle?

bruce750i · 01.10.2012, 04:55 AM

The top of the spur appears to be slightly leaning away from the motor mount. Is it me or has your pinion been losing some weight?

brian015 · 08:14 AM

Quote:

Originally Posted by bruce750i

The top of the spur appears to be slightly leaning away from the motor mount.

+1
Your spur does not appear to be exactly vertical - this means your mesh will not be perfectly aligned - and your pinion will be forced toward the end of the motor shaft and eventually come loose.

bumsnogger · 01.10.2012, 09:20 AM

Hi.I had the same thing with my MMM'd summit.I cut a dent in the shaft with a dremel.Hasn't happened since :)

brian015 · 09:27 AM

I guess the point some of us are trying to make is that pinions should not come off like this if they are properly tightened. The OP has already tried blue loctite with no success. It sure sounds like there's another problem and that simply getting the set screw tightened down on the shaft better is not the real solution. The misalignment of the gears appears to be the real problem.

Again, my experience with many different setups is that I've never needed to do anything special to keep a pinion on - except in the one case that I know my gears were misaligned - when I fixed my motor mount alignment, my pinion problem went away.