4200 XL shear pin repair

[Jack3M]

Have read many posts about the track system in the 4200XL. One broke the other day on me and I got inside to figure it out.

Seems there is just a shear pin in there, the rest is all metal and heavy duty. Of course this does nothing to change the speed, but if you are in a locale where parts are not readily available, this thread should be of assistance.

I have never done Picassa before, so have patience.

Turns out that 3 screws were loose in the gearbox to the motor also, these got locktite.

You do not need to take off any more than the track, do not remove the part that holds the motor and sprocket.

There are 4 set screws, two on top, two on front that hold the motor assembly in place. Loosen them. (No photos of this) Remove the cap over the motor (inside part).
https://picasaweb.google.com/1064737...85097387688866



Well don't seem to be able to figure out and cannot find the thread on how to!

[Jack3M]

So for now, until someone fixes this for me, you will have to click on the links.

The two little set screws on the outer cap that are 180 degrees from each other need to be removed completely, both of them


Mark positive pole on the motor and unsolder the wires to make this much easier.


Remove the cap. If it hangs, there may be broken pieces of the shear pin that interfere, this should just lift off easily. Then the motor comes right out.

[Jack3M]

Now you can remove the sprocket assembly from the motor, do not loose the O-ring. Also this is opportunity to grease the bearing with good waterproof grease. Picture shows the sprocket off. BUT if you look closely, there is an Allen wrench going through the very center of the unit.


This connects the motor output shaft to the drive sprocket. In many cases this will be enough to resolve the issue, I assume, lining up the hole and assembly I will describe a bit later as there is one not of importance.

[Jack3M]

You can see the hole in the output shaft in this photo.


But I noticed the gearbox was loose and decided to try to fix it. I had to remove 3 sets of gears to allow me to get to the 3 screws that hold the case and motor together. These screws got locktite.





https://picasaweb.google.com/1064737...85071549820722

https://picasaweb.google.com/1064737...85957591941298

[Jack3M]

Of note, I made a new shear pin out of a piece of mild steel I had. Not sure how hard it should be, not hard to fix this really. If just the shear, you don't even need to remove the motor actually.

But to line it up was difficult, and I learned that by loosening the 4 set screws for holding the motor and pulling the motor out toward the cap a bit, made it much easier to get the new pin lined up and in place. Put the keeper set screws back in. Then push down hard toward the O-Ring so that it seals the whole unit from the environment.

So, my benefit from all this is I saved a bunch of cash after having just gotten this. Also, that unit is not a bad piece of work, all the gears are metal. I just increased the amount of grease on stuff. Albeit slow, these units are pretty sneaky smart.

[TheBennyB]

You can also use a drill bit of 5/64" for a shear pin if your in a pinch.

[TheBennyB]

If you start to have failures or want a bit more speed/smoothness check out Soyland's upgrade.

http://www.rctruckandconstruction.co...ad.php?t=11276

[Stefan]

Originally Posted by Jack3M

Seems there is just a shear pin in there, the rest is all metal and heavy duty.

If what you wrote means that the shear pin is not metal then I´d be very reluctant to replace it with a metal pin, let alone a steel one, unless of course the next time you prefer the gears or the track to break rather than the shear pin

[Jack3M]

Stephan, the original is metal. If I want softer metal I could use aluminum welding rod.

[johnny88]

I will attempt to upload some photos of the entire process of replacing the 'shear pin'. I might call those pins the ' drive sprocket output shaft engagement pin'. The very first photo shows dirt piled up around the drive sprocket. You drive in conditions like this you will either snap the shear pin or break one of your tracks. I have done both.............the 4200XL is well made but you need to drive it with care. I will now try to upload a series of photos. (I have never posted on a forum)

[johnny88]

Here are the next 5 photos.........when you remove the 2 set screws from the drive sprocket cover, clean out the dirt from the hole to get access to the set screw. They are in about 3/16". If you don't have a nice Hex precision driver set I highly recommend Wiha #26390 for metric. Get their phillips driver set also -they will make you happy.













CLEANING THE THREADED HOLE WITH SET SCREW BURIED INSIDE

[johnny88]

The pin size is 2mm. The length is not critical as long as you are in the range of about 29mm - 37mm. I highly recommend purchasing at least a foot of this wire. I have broken 3 - 4 of these pins. The good news about the pin breaking is that as the weakest link, you are not breaking your track or your gearbox
I use the following from McMaster Carr.
2mm Softened (Annealed) Precision Ground 36"long 88625K61 $2.49

[johnny88]

one more set of fotos and then I am done with my first forum posting.........

[johnny88]

Last set of photos. As you can see to fix the shear pin you don't have to remove the track or the motor. If you grind a bevel on the end of the pin it will help with insertion alignment into the gearbox output shaft.

[sparkycuda]

Nice explanation and pics of the process! I haven't experienced this failure (yet?) but appreciate the time and effort you expended to cover the repair.

Thanks!

Ken

[johnny88]

thanks.