Forks will benefit from new seals if oil is leaking and you might as well replace the bushes at the same time. Give the forks a good clean, particularly the sediment that collects at the bottom of the tubes and refill to the correct level with a good quality correct specification oil. - This is generally a DIY job.
There are other changes that can be made:
1). The preload and general softness can be improved by getting a stiffer set of springs. If you make big changes here you probably need to make changes to the damping as well.
2). Increasing the oil level in the forks will increase air pressure / air spring assistance towards the end (last 1/3 aprox) of the stroke so make it harder to bottom out the forks. Do this in 10mm intervals and test all the time.
3). Increasing the viscosity of the oil (the weight) will increase both the compression and rebound damping. Standard is 5 or 10 wt this can be increased up to 20.
4). The forks can be changed. This has generally been done with fitting CR125 forks as these have the most combatible damping and springing characteristics. I have recently found that CR250 forks are only slightly firmer than CR125 so would be suitable though I believe CR500 to be too hard. Mk2s onwards (all those with USD forks) can be a straight swap CR - CRM (1991 CR forks fit but it appears that some others are not without some milling work ) but Mk1s require the fork yokes to be milled out from 41mm to 43mm to fit conventional CR forks. If you want to change Mk1 forks to USDs then you have to get new yokes (and retain the original steering post) and mess around with the front wheel spindle, bearings and spacers.
Early ninties (USD) forks seem to be the easiest to fit as some are a direct swap. These tend to have only compression damping adjustment but are certainly better than standard CRMs. The later you go then the better forks you get but also the more things you need to change (a selection of - wheel bearings, spacers, spindle, brake bracket, milling yokes, new yokes, steering post.....)
XR250R forks are a direct replacement for Mk1 forks. They are 41mm but have cartridge damping and are a lot better. They also use the same 15mm axle. 1990s - 2004 (last model) will do but as always later is better.
XR400/650 conventional forks are good, and probably the best, replacement for a Mk1, but they do require the yokes being milled out to 43mm.
Remember that when you buy secondhand forks they may well need to be serviced and this could mean new bushes, new seals and oil. Beware of nicks or rust spots on the chrome slider as this can kill seals very quickly and is expensive to repair.
5). You can get the forks resprung and revalved by a professional suspension specialist
-- Edited by delvey91 on Tuesday 19th of June 2012 03:13:47 PM
Hi I'm looking to upgrade the front end on my crm so I'm looking for some cr forks as I'm hoping that they mite just bolt on to my existing yokes ? has anyone done this or know what mite fit ??
I have a mk2 crm250 and changing the oil and seals made a massive difference, I'm 18 stone and 6ft2 and the bike is great for Laneing, I would not take it to a mx track with big jumps as I'm sure I would kill it, but for the lanes it's just great.
) but Mk1s require the fork yokes to be milled out from 41mm to 43mm to fit conventional CR forks. If you want to change Mk1 forks to USDs then you have to get new yokes (and retain the original steering post) and mess around with the front wheel spindle, bearings and spacers.
