bmw_rider Posted December 31, 2005 Share Posted December 31, 2005 Ok, How big of a job is it to replace the fork springs on an 85 K100RT? I am considering lowering the bike for my son to ride. (Short inseam.) Thinking along the way of putting the progressive springs in the forks. All constructive input welcome. Thanks. Link to comment
Bruce C Posted December 31, 2005 Share Posted December 31, 2005 I think most riders simply slide the forks up the triple clamps when lowering an old K-bike. and get a shorter shock. Measure your existing height on the front and rear of the bike so you can keep it on the same plane after you lower it. Bruce C Link to comment
bmw_rider Posted January 1, 2006 Author Share Posted January 1, 2006 Yep, I was already planning on doing that with the forks, thought maybe progressive springs would firm it up a bit. Link to comment
Bruce C Posted January 1, 2006 Share Posted January 1, 2006 If you just want to tighten up and take out some of the pogo stick effect on the Fichtel & Sachs front end. I changed the oil to 15wht. Spectro fork oil and filled them to 370cc. This is 10cc. over stock, but within specs. I admit it's not as good as new springs, but I sure didn't complain with the final result. I don't believe that new springs will take out the pogo effect of the stock forks, but I also know that people will dis-agree with me on that. Bruce C Link to comment
ShovelStrokeEd Posted January 1, 2006 Share Posted January 1, 2006 The proper way to lower the front of the bike via forks is to remove and disassemble the fork legs and install a longer top out stop at the bottom of the damper assemblies. That way you will remove travel from the forks. A secondary benefit is you will be compressing the fork springs a bit more and so may be able to ressurect the more than likely badly sagged stock springs. Progressive springs work pretty well in that application but I have had some bad luck with them breaking over the years. Might want to look at something from an outfit like Traction Dynamics. Doubtful they will have anything specific to the BMW but you should be able to find something that will come close for diameter, rate and free length. The actual work on the forks is very straightforward. Remove brakes and front wheel, Crack but do not remove the plugs on the top of the fork. Loosen clamp bolts at triple clamps and slide the entire assembly out of the triples. Now for the only special tool you need a long 6mm (I think) Allen socket and an air wrench to unscrew the damper rod bolt from the bottom of the lower leg. Get that loose and then, using a vise and some rags for padding, carefully remove the top plugs. They shoudln't have much spring tension on them at this point. Tilt the fork up to drain the oil, catch the spring and damper rod as they fall out. The spacer you want to change is at the very bottom of the damper rod, just take off the nut and replace with a longer spacer. I think they might have a spring in there as well, you can discard that and make the new spacer to appropriate length. Wash out the lower leg and make sure everthing is clean. Now would be a good time to replace the seals as well. Re-assemble in the reverse order. 15W fork oil is not a bad idea. Use the factory recommended amount. Link to comment
bmw_rider Posted January 2, 2006 Author Share Posted January 2, 2006 Thanks all. I need to think this through a bit more I can see. Link to comment
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