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Fixing sloppy Hornbag forks.

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by Loz, Aug 26, 2006.

  1. Just finished servicing and slightly upgrading the forks on the 900, thought I'd pop something up about what I did and the effect it seems to have had.

    The Problem
    The bike is now over 50,000k old and the suspension has been pretty sloppy of late. Dive under brakes has been unacceptable, speed bumps have pitched the bike back and forth way too much, back end is bottoming out a bit under heavy cornering, wallowing a touch... It's been slowing me down in the twisties and robbing me of riding confidence.

    The Hornet 900 has what you'd call "budget" suspension - non-adjustable forks and a rear shock adjustable for preload only. It's set up to handle riders of about 60-80kg, not a fat mongrel like myself weighing in at nearly 120. And while it's coped for a while under this overloading, the suspension is well known to deteriorate with age.

    The fix
    Heavier weight fork oil to increase compression and rebound damping, and a set of new springs rated for the combined weight of the bike + lardarse here.

    Yanked off the front end, got the forks out, tipped out the FILTHY old fork oil which Glitch changed for me about 12 months ago... Wow, gross! That stuff fouled up real good real quick. Pulled out the springs, left the forks to drain.

    Took the springs down to Promecha, bought new heavier springs for $190. They're shorter, so I picked up some extra collar tubing and a stack of washers too.

    Plonked the new 15W fork oil in, measured it up for the right levels etc. Put in the springs, collars and washers, put the fork caps back on.

    In order to set the 20mm preload on the springs like the Promecha dude suggested, I pulled the fork tubes up to the end of their travel and measured the distance between that and the top of the fork caps. At this point you can add or remove washers or collar spacers to change the preload on the fork springs if your bike is like mine and has no adjustment available.

    Then it's compress the spring, screw the fork cap back on, do the same with the other fork and stick your front end back on, making elaborate and often unnecessary use oof a torque wrench if you happen to just have bought one. :grin:

    The Effects
    Wow. I'm not much good at understanding what's happening with suspension. I know when it's good, and I know when it's bad. Fiddling with this stuff and riding the Hornet afterwards has been very educational.

    The geometry of the bike is now noticeably different. The front end no longer sags nearly as much when I sit on the bike, so it sits higher. The poor old rooted rear shock still sits pretty low.

    This has also changed the steering geometry, making the bike less quick to turn but adding a feeling of stability in faster corners. I'm missing some of that chuckability at slower speeds, I might reduce the preload to address this if and when I can be buggered jacking the mongrel up and opening up the forks again. Shouldn't be so hard now I don't have to change oil - I shouldn't have to take the front wheel off, I might even be able to do it simply by sliding the forks through the triple clamps a bit to get access.

    The fresh, firmer spring feels fantastic over bumps and speed humps etc. It's no harsher a ride than the old spring (perhaps due to increased damping from the heavier oil) and it feels much more solid and dependable everywhere, especially in corners. It doesn't dive as much under brakes - although there's still more dive than I'd like after feeling what the '06 Blade is like on the stoppers.

    Promecha reckon a $400 revalve and set-up can turn shit into gold and that the spring-and-oil job I've done here is missing out on more than 50% of the benefits. If I had the cash, I'd get them to do it. The difference in feel is fantastic, it's really rejuvenated the front-end handling and I'd love to feel it revalved and set up for anti-dive.

    Looking Forward...
    I don't know if there's a quick and cheap way to similarly breathe life into my rear shock, which has been abused like a red-headed stepchild (for a while there I used to wheelie over speed humps, do a little back-wheel jump and try to keep the wheelie going when I landed. Real clever.) so I've nobody to blame by my own exuberant self there.

    Again, Promecha have quoted a little over $400 to re-funkify the rear shock, which, now that the more sorted front end is drawing attention to it, is going to play on my mind. It sounds a lot more complex than the fork stuff I was happy to play with myself.

    So there ya go, hope that was interesting, or helpful - the job was quite straightforward, it was a great learning experience for me (I finally understand what I was helping Glitch with last year), and I'd recommend it as a pretty cheap way to beef up a sad and sorry front end, either one that was originally undersprung or one that has deteriorated through age.[/img][/list]