Kraton Kraton pinion won't stay put

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chrisexv6

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Arrma RC's
  1. Kraton 6s
Recently purchased a pretty well modded Kraton 6S. The only real issue we've been having is the pinion moving on the shaft.

Yesterday afternoon I reinstalled the pinion with red loctite on the grub screw (nothing on the shaft). Basically 24 hours later we use the truck and the pinion slid.

BUT it seemed to have happened right after using reverse. When I tried to take the pinion off, the grub screw would not budge....had to heat it up to loosen it, so it looks like the red loctite did its job.

Any other suggestions to keep it from sliding? Is it a common issue for it to work fine in forward but slide on the shaft in reverse?

Thanks.

-Chris
 
The grub screw could be really worn at the tip? And are you sure it's the pinion sliding and not the shaft? Grab some pliers and pull back and forth on the shaft... is there any slop?
 
Its definitely the pinion....I basically set it roughly flush with the end of the motor shaft, after a few runs its back from flush and hitting the motor mount plate.

Just to be sure I did pull the motor and try to slide the shaft but there is no movement.

Grub screw looks OK, Im wondering if maybe the motor was on an angle compared to the spur gear. Its hard to tell since its pretty blocked with the ESC, looking down on the truck the motor doesn't look straight, but it could be because of the angles of the chassis (perfectly straight points of reference are hard to come by)

Looking across the pinion to the spur it looks better now (we redid the pinion loctite along with realigning the motor).

Just frustrating because we haven't been able to get a full pack out of it yet, because the darn pinion keeps moving.
 
I use knurled grub screws for my pinions and when I can, I run 2 screws and blue loctite. I have a lot of issues but never an issue with that since I started doing it this way. Overkill? Probably but I had that issue with my typhon and it infuriated me.
 
You can try removing the motor mount and checking it on a straight surface...

The only other reasons for it I can think of is the thread lock you're using isn't up for it, or the pinion threads might not be clean and has dirt, grease or cutting oil residue and is preventing the thread lock from curing

Do you have any birds eye view pictures of the motor/centre diff? Of the pinion?
 
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Thanks for the replies! I will try to answer them here :)

The last time the pinion moved, it was clear the red loctite was tight...I needed to heat up the gear a bit just to turn the grub screw. Im not sure if maybe that just means the screw itself didnt "screw in" tight enough to the shaft. But all seemed well until we tried to use reverse, after that we got the clicking we're used to hearing when the pinion slides.

We are going to try and run it again today, if it moves I will tear it all down (again) and be sure to clean everything with alcohol - motor shaft, pinion, grub screw and threads. I don't have a brand new pinion (yet...we have one on the way) so Im trying to work with what we have. The knurled grub screw is a great idea....Im honestly surprised they don't come that way already, unless its possibly going to cause damage to the motor shaft?

Something I did notice - with the pinion off, if I try to screw thee grub screw in, it doesn't go all the way through. It screws in enough to make the round hole look like a "D" so I *think* thats all that is necessary, but I wonder if the threads are preventing it from really tightening down on the motor shaft. Should the screw be able to go all the way through the threaded hole?

I am using Wera 2.5mm hex "blade" in a System 4 handle. Its a tool set that has held up for 10+ years, so I can get plenty of torque on the screw. For poops and giggles I might order an MIP set, but I don't think the tools are the issue (maybe the USER of the tools :) )

Attached are a few pics....its hard to see inside of everything when its assembled. The pinion is a little worn, its all I have right now. The mesh should be good. The gears look to be in the same plane as each other (i.e. pinion is parallel to spur), etc. Ill try to see if I can get better pics if that will help.

Thanks again.

IMG_20200617_090308.jpg

IMG_20200617_090321.jpg

IMG_20200617_090345.jpg
 
Thanks for the replies! I will try to answer them here :)

The last time the pinion moved, it was clear the red loctite was tight...I needed to heat up the gear a bit just to turn the grub screw. Im not sure if maybe that just means the screw itself didnt "screw in" tight enough to the shaft. But all seemed well until we tried to use reverse, after that we got the clicking we're used to hearing when the pinion slides.

We are going to try and run it again today, if it moves I will tear it all down (again) and be sure to clean everything with alcohol - motor shaft, pinion, grub screw and threads. I don't have a brand new pinion (yet...we have one on the way) so Im trying to work with what we have. The knurled grub screw is a great idea....Im honestly surprised they don't come that way already, unless its possibly going to cause damage to the motor shaft?

Something I did notice - with the pinion off, if I try to screw thee grub screw in, it doesn't go all the way through. It screws in enough to make the round hole look like a "D" so I *think* thats all that is necessary, but I wonder if the threads are preventing it from really tightening down on the motor shaft. Should the screw be able to go all the way through the threaded hole?

I am using Wera 2.5mm hex "blade" in a System 4 handle. Its a tool set that has held up for 10+ years, so I can get plenty of torque on the screw. For poops and giggles I might order an MIP set, but I don't think the tools are the issue (maybe the USER of the tools :) )

Attached are a few pics....its hard to see inside of everything when its assembled. The pinion is a little worn, its all I have right now. The mesh should be good. The gears look to be in the same plane as each other (i.e. pinion is parallel to spur), etc. Ill try to see if I can get better pics if that will help.

Thanks again.

View attachment 85967
View attachment 85968
View attachment 85969
Try an old ball from a bearing before the pinion grub
 
One issue I've seen, old loctite prevents the screw from bottoming out. Easy way to check, screw it in all the way with the pinion in your hand, if it gets stuck you have to clean it out. I use a threading tool for cleaning but anything will work.
This is not a common issue and there are no big secrets. Pinion thread and screw must be clean, no oil or dirt, I use blue loctite on screw alone, no issues. There definitely should not be any issues with red, it must cure for 24h and don't fiddle with it after 20 min or it will not bond correctly i.e. set the mesh but don't spin it up etc.
Ball would help even in this 'blocked' condition i.e. that is a solution as well.

Pointing out the obvious, the screw must engage the shaft on the larger 'flat' portion of the shaft, will not hold on the rounded section. There are 2 flat sections, use the larger for the main screw, the smaller is for a secondary that some pinions provide. Looks like you did that though.
 
Thanks....and yeah the grub screw did not go all the way through the pinion, so it probably needs cleaning out. Will try the ball bearing idea, if I can find a ball that fits. New pinion on the way and should arrive Friday or Saturday, so I might just go that route and keep the existing ones as backup.

I did not see 2 flats on the motor shaft, its not a stock motor though. I am wondering - who makes pinion gears with 2 set screws? The most recommended ones (RRP, Tekno) don't seem to have 2 screws, I haven't found any other brand that does, either.
 
No idea who makes them with dual screws, I use Tekno and stock Arrma types. They serve me well enough.
I do have some with 2 screws but they were cheapos from Amazon and they are not recommended, they lasted maybe 10 sessions and then the teeth are gone. Stay far away from no-name pinions.

Might be cheaper to buy a thread tap, standard for pinion is M4. A set is cheaper than a pinion and lasts forever.
I usually put them into a very low rpm drill or just but a handle to go with it. Threading is to be done very slow i.e. 1 rpm ;)
You could just burn it off with a flame or mini torch.

Tap set example:
https://www.amazon.com/M3-M4-M5-M6-...thread+tap&qid=1592428390&s=industrial&sr=1-4
 
No idea who makes them with dual screws, I use Tekno and stock Arrma types. They serve me well enough.
I do have some with 2 screws but they were cheapos from Amazon and they are not recommended, they lasted maybe 10 sessions and then the teeth are gone. Stay far away from no-name pinions.

Might be cheaper to buy a thread tap, standard for pinion is M4. A set is cheaper than a pinion and lasts forever.
I usually put them into a very low rpm drill or just but a handle to go with it. Threading is to be done very slow i.e. 1 rpm ;)
You could just burn it off with a flame or mini torch.

Tap set example:
https://www.amazon.com/M3-M4-M5-M6-...thread+tap&qid=1592428390&s=industrial&sr=1-4

Hot Racing makes the output shaft cup and had 2 grub screws, for the Kraton
 
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