Originally Posted By: 660mag
Gear boxes should be less than 50% lube. Grease does not transfer heat well, but air does. If you fill a gearbox all the way up with lube it will get hotter than [censored], and hot very quickly. After a gear box has lost some of its grease it will actually run cooler.
If your gear box on your trimmer has a service port then you can change out 98% of the lube without taking it apart.
Get the gearbox warmed up by running for a few min, and remove the service screw. Point the hole on the gearbox away from you and blow compressed air across the service port until all the grease has sprayed out. Try to blow it on a towel to prevent a mess. Those gearboxes use a high sulfur grease like this stihl part number. #0781-120-1117. Estimate the volume of the air space in your gearbox, and fill to aprox 40% by volume. Enjoy. If it has no service port remove the bump feed head. Then remove the output bearing from the gearbox housing. You will need a pair of internal snapring pliers most likely, and a heat gun. A butane torch is too hot. remove the snapring, and heat the gearbox to aprox 240f. The bearing should fall out when tapped on the ground. Remove the factory grease with compressed air, and fill to 40%. Put the bearing in the freezer for 10 min, and reheat the gear box housing. The bearing will fall in to place. As the bearing warms up, and the housing cools off(about 10 sec) the bearing will be cold welded in place. There is a lip that keeps the bearing from going to far in so seat it all the way in.
Hmm, interesting info here.
My Echo SRM-210 has a "grease port" on the head. It says that it takes lithium grease. That's what I found it full of and that's what I replaced it with when I tore into it one time. It would be nice if they used a fluid bath like differentials instead of grease that you need to balance this air space against actually getting grease in the right places.
Maybe I should crack into it again this spring just for "fun". On the other hand if it isn't broke....