Tighten a loose freewheel on the trail

 I have had bicycle freewheels come loose while riding, many times and on multiple bikes.  Here is a video showing it.

You start to hear and feel a knock, worse in some gears that others.  As it progresses, it may struggle when changing gears.  If you let is continue, it will come apart and leave your stranded.  

Maybe I am the only one that seems to have this problem but I doubt it.  The first time this happened I was out in the desert up a long hill.  I felt it happening but did not stop to check into it.  It finally got so bad the freewheel came apart and locked so there was no ratchet action anymore and the pedals just followed the wheel.  It made for a long trip home.  My bike was under warranty so I got a whole new rear wheel assembly.  The new one did the same thing.  This time I caught it early.  Normally you need to take the wheel off and use a special spanner for this.  I only had some basic tools I carry on the bike.  I finally used a Philips screwdriver and some ingenuity to tighten it back up without taking anything apart.    

Here is a photo showing the freewheel off the bike so you can see how to place the screwdriver.

There are small holes for the spanner. Push the Philips screwdriver into that hole at a bit of an angle. Since the bike will be assembled on the trail, there are only a few areas where you can even see this part of the freewheel.  Generally in the slot where the axle bolts to the frame.  While pushing in hard on the screwdriver, rotate the wheel in the forward travel direction.  This will cause the whole freewheel to move with the wheel but since you are holding the freewheel nut with the screwdriver it will stop against the frame and tighten the nut.  Since you have the leverage of the whole wheel diameter, the weak point of this is keeping that screwdriver held tight into the nut hole.  You can help this by holding the screwdriver at a bit of angle.  Hard to explain in words but it works well.  

The freewheel bearing preload is set with shims, not a specific torque, so you really can't overtighten it, especially since the screwdriver approach does not give enough grip to overtighten it.