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Only $10 for all 2024 SX, MX, and SMX series (regularly $30).
I look forward to doing some of the tuning mods you guys are using to get the most out of these old school forks.
The Shop
There are two more good reasons about using these forks for off road riding. Since the forks are only 43mm they flex a bit, which isn't a bad thing off road. This allows the front wheel to move around without that deflection going to the bars. This allows you to not need a steering stabilizer as the bike tracks straighter. Secondly, the aluminum sliders on these conventional forks take the abuse of off road riding without risking dinging or scratching the chrome fork tubes of modern USD forks. Finally, I can't recall ever putting new fork seals on the 3 sets of these forks I have owned and ran. Wish I could say the same for USD forks. Enjoy...
Does anyone have information on recommended shims stacks for an 87 CR125, vintage racing on natural terrain tracks. No real complaints with what I have just checking to see if it can be better.
I want to add a comment and recommendation to my original post on 7/17/2019: After riding the modified Showa 43mm forks on my 1997 Honda XR650L I figured it would not be best to drill the four 7/64" holes between the square ports on the mid valves of these Showa 43mm forks. See original post for what I did here. This causes the forks to dive a little too much under heavy front wheel braking.
BTW: I have recently swapped out the OEM modified Showa 43mm forks on the XRL for a nice set of Gen 1 Showa 47U forks from a 2001 Honda CR250R with my CNC machined base valves and good valving. Even though the 43s worked great on the XRL they flexed too much due to the weight of the bike. The 47U front end (forks, triples and front wheel) now weighs about 3 pounds less than the OEM 43mm set up. I have removed a little over 30 pounds of fat off the XRL.
I have an 87 CR125 that I'm using for vintage racing. The upper fork tubes are badly pitted between the triple clamps but otherwise have worked well since I bought the bike 18 months ago. The only thing I've done is change the oil.
I bought a pair of 87 CR250 forks on ebay to use for parts. My intent was to use the best parts from each fork to build one good set. I also wanted to replace the bushings and seals since their condition was unknown.
So I tore down all four cartridge assemblies, the two from the 125 and the two from the 250. All four still had the factory peening on the valve assemblies, so I assume they are factory. None of the four are exactly the same, both the 125 and the 250 are mis-matched left to right. And the 250 had a single 18mm x 0.1shim on the base valve.
I'm looking for an optimum shim stack for vintage racing, natural terrain tracks, old and slow.
Most unusual, as I have never seen different valving per leg on these or any forks that have both compression and rebound in both tubes. The '87 forks were very good with stock valving. The 125 forks will have lighter valving and springs due to the bike being lighter than the 250. There should be a sticker on the back side of the aluminum sliders with a number. This number is the valving for the forks. If you can still read them you should see different numbers for the CR125, 250 and 500. Remember that these forks will have been valved and sprung softer for natural tracks and terrain. Nowadays computer designed supercross tracks have big jumps and air time and bikes require stiffer (springs and valving) suspension. I know the Showa 43mm forks worked great out in the Mojave Desert as I used to race my 500cc 2Ts up sand washes at 70+ mph in the mid to late '80s. This was as natural as you could get.
If you have to remove the peening be careful not to file or grind the end of the threads square. Same for rear shocks. Instead bevel the grinding of the threads as you don't want to remove the center of threaded post where the hole is by shortening it. Sometimes the hole can be larger in diameter as the post gets ground away. I always use new nuts with a drop of red Loctite and light torque on the fork valving nuts. Use red Loctite and good torque on shock valving nuts.
I wouldn't use anything but a good quality SAE 5 fork oil and SAE 3 for shocks. I use Maxima blue label SAE 5 for forks and their purple label synthetic SAE 3 for shocks. Some people use heavier oil in these Showa 43mm forks to control rebound. This will stiffen up the compression damping, which is what you don't want if your valving is correct. You can control rebound a little on these forks (there is no external adjustment) by slightly closing up both rebound holes that are located just under the nut that locks the damper rod to the fork cap. I'm only talking about .010-.015". To do this first measure the hole diameter as close as you can with the shank of a small drill. Number drills go down to a #60 (.040") in a standard set and get larger by a few thousandths as the drill number decreases. The holes will be around .060". Carefully dimple in the holes using a V-block to support the damper rods. You don't want to bend or crush the inner damper rod. You just want to dimple in the outer edge of the rebound holes slightly. Then you will have to carefully drill the dimpled hole to the size you want to assure they are all the same. Use a drop of oil to lubricate the drilling. I would start about .015" smaller than stock and go from there. Clean all chips from the inside of the damper rod. I wouldn't deburr the outside of the hole as that can enlarge the drilled hole.
Another thing: I always try to enlarge the compression holes on all fork and shock valves. This reduces the possibility of harsh hi-speed compression damping. On sudden hits (square edge ruts, etc) the suspension has to compress quickly (IE: high speed compression damping). Opening the compression holes in the fork and shock valves allows for more oil flow when it is needed and reduces the spike you feel in the bars that make your teeth rattle. Then the compression damping can be controlled better with the shims, not the hole size. Of course, the valving still needs to be spot on.
The springs are sacked. Honda sets the free length service limit at 22.47" and mine are at 22. I believe these are stock 0.339kg/mm, when I measured them with the bathroom scale and broomstick method I got .35. If they are .35 they are not Honda as they don't have the closed coils Honda describes. Honda lists .31, .33, .35, Racetech recommends .38 but the closest match is .40. I weigh 180lbs and am old and slow, I like the soft suspension I have today but do expect to get faster as I go. I will likely get the .35 Honda springs.
Base valve- 2 x 18.2, 5 x 18.1 This adjusts the mis-match I had in the left & right side, otherwise it's about what I had previously.
Rebound- 5 x 18.1 This is the same as it had, no change.
New bushings and seals.
Use the good upper tubes from the CR250.
5wt oil
I agree, this old thread was too full of good information to let it die.
I have my '87 CR125 forks back together and can tell you what I ended up with. I haven't had the bike out yet to judge the results.
Please post what you find in your forks when you take them apart and how to set them up. I've torn down two sets and found very different setups in each.
There is also a thread on the same subject on TT if you are looking for more info.
Pit Row
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