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As this comes up regularly and is a real pain if you don't know some tricks, here's a safe mechanical way to swap head bearings. Remember that to achieve anything of note, a little sweat is required. Some arc weld the head races so they drop out after cooling. Some dremel the races out and the bearing off the triple tree. Whatever works, but I don't have a dremel tool or welder, want to spend an afternoon with sparks, like to flame my paint nor mar the race/bearing seats. I like doing it the right way the first time (as if there's enough for a second). If you're looking for a room-temp, non-destructive, mechanical way to change them, read on. The top bearing is simple; you just tap the triple tree stem down to get it off and screw the adjuster nut onto it to put the new one on.
The races in the headstock are trickier, but can be swapped in 15 minutes with practice (friends' bikes in my case). I use Ed Korn's puller (see Cycleworks). You can also buy an internally expanding race puller, but they're more expensive and often not as effective. Borrow or buy his tool as the time and scraped knuckles it saves makes it cheap. Do not use the bearing rollers to press the races in! Metal is not truly solid, it bends; it flexs; it fatigues; it dents; it breaks regardless of strength. You are likely replacing the bearings because they are brinnelled/notched. Pressing races in with the bearings just jumpstarts the demise of the new ones. The races have roughly a 1/16-inch lip on top and are 2-inches across. You could tap them in with a hammer and a block of wood using an old race to tap bottom one in which is countersunk, but they can get cockeyed this way. A piece of threaded rod at least 1/2-inch in diameter (bigger IS better), two thick washers with a 2-inch outer diameter, two thick washers with a 2+-inch outer diameter and a pair of nuts. Stick the rod down the headstock, and use the washers and nuts to screw press each race home one at a time (sometimes letting the races sit in a bag in the freezer overnite helps). You MUST keep all parts centered and can use band clamps to help. If the washers begin to cup, the race is home. This method also allows all work to be done topside for both races and doesn't rock the frame. NOTE: ALL bearings, even well-installed ones, settle in (no, pressing the races in with the bearings is not a substitute). The bearing's adjustment should be checked 250, 500, 750 and 1,000 miles after being replaced, or each time you gas up, as they tend to loosen up a smidge. There is no commonly available 'pretty' way to remove the bearing from the triple tree, but you clean it up a bit by breaking the bearing cage with a screwdriver and removing the rollers (take safety precautions as the rollers can fly out). Some options are grinding a slit in it with a Dremel tool if you can avoid cutting into the triple tree. You can have a BMW dealer do it for you when you buy your head bearings, but if they won't let you watch or want to charge you a full hour to do it (only takes a couple minutes with the correct tool), you might consider these routes. Below the bearing, there should be a dust cap made of thin metal -- make sure to replace it with a new one. Below that, there are two recesses 7mm wide and 4mm tall (1/4" x 5/32") on either side of the bearing for the hooks of the BMW puller to grab behind the race (which is why you ask to watch the dealer to make sure they use them). I REALLY hate to pry against aluminum base of the T-tree, but sometimes a pair of hooks from a small bearing puller can be used as pry bars in the slots below the race to at least get it started. Others drive a chisel between the dust cap and the bearing to get it started keeping the flat side against the aluminum and the bevelled edge against the race. Since you need to clamp the T-tree to do these, make sure to use wooden jaw protectors in the vise and to clamp only on the ridged central portion of the stem, not the polished bearing journals/seats, just enough to hold it. If you're handy with a torch (yeah, I know I said room temp, but it makes it easier), it helps to heat up that inner bearing race but keep the heat away from the stem and the aluminum as much as possible. A square-end punch and hammer can be used to drive off the race by striking its upper lip down and off the stem, alternating sides as necessary. As soon as the inner race moves off the lower journal, it'll slide up the stem and stop on the upper journal (you're home free at this point ). Loosen the vise jaws and let the T-tree stem hang between the vise jaws so that the inner race rests on top and tap the stem top down through the race (save the race for later). Feels good, don't it? Remove the old dust seal from the T-tree and replace with a new one. Grease up the new bearing, wiping off any from the bearing surfaces that seat against the T-tree or its stem and place it on the stem. Invert the old inner bearing race and place it on top of the new one. With a 6-inch long piece of thick-walled pipe with a 1 1/8 to 1 1/4" inner diameter, drive the new race down onto its seat. The old race will keep you from crushing/distorting the new bearings cage. If you have the piece of threaded rod you used to seat the races in the headstock, you can also use it with the pipe and appropriate nuts/washers to press the new bearing home by putting the rod inside the triple-tree. Drift off the old inner race in the manner mentioned above though it will be much easier since only a fraction of it sits on the lower bearing's journal. Tighten bearings as per specifications, generally enough that the handlebars will fall to one side and stop at/before the steering stop, but not bounce off of it. A low speed wobble while decelerating down a small hill often indicates they're a little loose. A bike that constantly needs steering correction or tends to 'hunt' to one side then the other often indicates they're too tight, but all this might be best covered in another article. Now go out and ride! Cautiously! Joe #3335
'78 R80/7 |
