Advice on changing a starter on a 125

[ultracajun]

I am trying to change the starter on my son's 125. It has the 3 main bolts with the phillps head scews next to them.

In trying to get the old stater off I noticed that it was held on by a internal chain instad of gear teeth. I was afraid of this chain falling down into the motor so I remounted the old starter until the new one comes in.

Any advice on how to take off and reinstall this type of starter without problems?

Thanks.