It depends on the bike, but I've done this for years with many different brands of motorcycles. You've apparently taken the triple clamps off the bike. Is there a top and bottom seal to keep water and dirt out of the bearings? Look in the frame headstock tube to see if there are any open holes to the connecting frame tubes. If there's none this will work, other wise you'll fill your frame will grease. If you have no holes and grease seals top and bottom, drill a correct sized hole in a spot on the side of the headstock tube in a place that will not interfere with anything and tap it to install a grease zerk. Oh yea, make sure you can get to it with a grease gun. Install the zerk, clean out any metal filings and put it together. Now pump it full of grease. Give it a pump every time you wash the bike or at intervals of your choosing. Sometimes a little grease may come out the bottom seal. If you pump it to full you'll get grease out every time you ride until it stabilizes. You know you have your bearings encased with grease. I normally try to place the zerk near the top. As you pump in the grease, gravity will make it naturally flow down to the lower bearing and you don't get grease to the upper bearing until the tube is full. If you have it full of grease it should keep the water out. This is a low speed operation so the bearings should not over heat and fail due to to much grease.