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Dirt Bike Mods & Maintenance
Lowering The seat hight on my KTM
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[QUOTE="rollingp, post: 227931, member: 25488"] 02 forks use 01 sxs valving and internals. 02 ktm shocks are almost as easy to service as japs. the air can be bled without the use of a evac pump.you still need a charging stand for the nitrogen. Yes I was involved with the factory testing of the 98 pds suspension . Usually if a straight rate feels plusher though the entire stroke it is a sign the spring rate should be changed to the next lowest number . It can indicate the spring is riding in the firm part too early. This is why trying different springs of the same rate is important. One spring may be at 1025 lbs at 3 inches of compression and the other may be 1000 and both springs are advertised at the same rate . Some will say that is not enough of a difference to tell but it is. It is noticeable once put on the bike especially if both springs are starting out about the same numbers on the first three coils which is the softest part of the spring. This is where I am referring to coil bind not the entire spring. Whether you believe it or not Kelly was running a bone sock production bike while racing the 4 stroke nat. When he came up short at Red bud and ripped the motor out of the frame made the steering stem look like an s and crushed the front wheel he was on a bone stock production bike . Even the suspension was stock except for the shim valving. He finished the series on a used exc that was at a dealer. They revalved it for mx and geared it. KTM didn't even want to give them titanium axles, swingarm pivot. or steering stem until this happened. Dowds bike for 01 was the platform for the 02 production bike. His motor was bone stock and de tuned for less hit off the bottom That bike is as stock as it gets except for the ti pivots and some fasteners. Also the pipe. Triple clamps and dampener. KTM has a sell what we race attitude. Even Dowds shock is completely stock except for the shim valving and he runs a PDS spring 8.0-10.3.and has tried the bladder. Spacing a pds shock isn't a good idea because you are losing some of the shock efeciancey. Especially on small acceleration bumps. The first piston in this shock does 95 % of the work very much like a normal link shock the second piston is along for the ride until about the last 1 inch of stroke. This is where the needle mounted inside the shock body at the very top enters the shaft and restricts the oil and diverts it through the second piston and its shim stack. Loosing any initial travel on the first piston results in loss of some efficiency and why would you want that? You wouldn't skimp on anything else on your bike Would you run a champion spark plug in your bike to save $5.00? Ktm lengthened the 02 shock shaft to give you what you are talking about giving up to some degree by putting a spacer in there. I have ridden all the 02 KTM bikes this year and yes the 2 strokes are not as plush as the 4 strokes but this is more to do because of the engine differences. We didn't have any trouble getting the two strokes to be plush . Yes we revalved the shock for more high speed comp. Got way away from the stock clicker settings and backed off the pre load on the forks went to the lightest oil and ran from 120 to 160 on fork oil levels . I am not saying valving the forks wouldn't make them better but we did just the shock and made a few spring changes. So far everyone is happy with that. I am not the doctor here but I am sticking to my guns about the relative ease in which to get these KTMs to work. I still feel most of these bikes have much better suspension action out of the box than any jap bike I have had over the last 20 years. If you really want a set of forks that work great try a set of 98-99, 50mm conventionals with a summers racing fork brace. They have a large bottom out cone and hold so much more oil than an inverted. The action is plush and there are some benefits to the lower center of gravity. The only fall back is they flex to a degree but for the average guy it is not a concern especially with a fork brace. Most cant get past the hype about the flex part. We ride mostly high speed open tracks and these forks are almost like cheating. The 4 stroke is awesome with these. Yes to a degree the inverted forks can be valved to be much better but it is almost impossible to duplicate the bottom out action of the 50mm white power forks. Just by the shear size of the bottom out cones and the hydraulic lock they provide. The inverted forks don't have the space to duplicate this. Remove the seals and tighten the springs and keep the dust wipers clean and they wont leak. to cut the subframe : make a mark about 1.5 inches above the lower subframe mounting bolt. Remove the seat, silencer, number plates, fender , shock flap and the sub frame. Remove the air box . Cut 5mm out of the subframe where you made the marks on each side. clamp the subframe lightly in a vise and file a chamfer in the cut ends. Also do this with the pieces that are cut off and must be tig welded back to the subframe. Take a straight edge and using two welders clamps return the cut off pieces to the sub frame. Use the straight edge to check for plumb at all sides while clamping. Use arcaloy or another welding brand of cleaner to clean the areas to be joined. Pre heat the two parts with a propane torch but just to warm it. Tack the pieces together making sure not to let it pull from the heat ( they must stay as straight as possible.) Weld it together and leave the bead. Grinding it off will weaken it. Use some polish to brighten it back up. Put everything back together. You will need to loosen the bolt that holds the two headers together and the rear header mount bolt. The extra play will let you get the silencer back on . The bolt holes will be off just enough to not go if you dont loosen the header bolts. The 5mm will lower the seat about 15 mm. This doesnt sound like much but when you sit on the bike it feels like allot compared to stock. It is noticable looking at it from the side. The bikes we have done this to reacted worse to turning on tight tracks until we slid the forks up and got a balance. 10mm We ran the shock at maximum allowable preload. Going to the 18mm offset worked even better. The ride is much flatter. We cut one bike down 10 mm and had to make a silencer bracket. The tire destroyed the fender and the air boot developed a hole. But this is what the owner wanted to try. 5-7mm is a good range. PS> I want to make it clear I am not talking about what Honda, Yam, or Kaw uses on there pro teams. Everyone knows they run as much high end works components they can get away with. They sell a much inferior product to the public. I am talking mainly about what KTM does. Dowds motor was never taken apart until the race at Red Bud when it was shipped back to ktm to be autopsied. It had all that time on it. This is a fact. Also no disrespect but we are mx racers not woods and most of this info from my post is for mx racing. A stock sx would be a ***** in the woods. You say allot of suspension companies dont want to work on the KTM shocks. Doesnt this tell you that they dont understand how it works, They are very easy to service and because of the steel body dont reguire as freqeunt a maint. schedule. The system is a good one and for bottom out control works better than most link bikes. It is simple simple simple. The 02 is the easiest to work on .The shaft nut screws off and doesnt reguire grinding. You need two screw drivers, an open end wrench to fit the shaft nut, a charging stand ( make one ) some nitrogen ,oil and a caliper. It takes no more than 20-30min to revalve a KTM shock and about 3 min to put the spring on ( compresser) Unless you are changing needles ( diameter and length or drilling bleed holes(98-99) they dont require much effort. Anything before 01 you had to evac the oil as you filled the shock using a closed pump unit otherwise the air would get trapped especially on th 98 because the oil had no free bleed and had to run all the way through the shaft to the bottom and back to the internal body.I have seen shocks that were done by reputable suspension companies come back with trapped air and over or under charged nitrogen levels.The most difficult task is making darn sure the air is out and the correct nitrogen pressure is used. The piston must me located in the correct height when charging after filling with oil.Remember the nitrogen piston only moves about 5 to 10 mm back and forth. Also I am not saying you should be able to flat foot the ground but why would that be so important? I am saying you should be able to touch the ground ( balls of your feet ) and 105 mm of rider sag is not a squatted bike and results is no adverse effects at least the bike has all its shaft travel to use. Lets Ride! [/QUOTE]
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Lowering The seat hight on my KTM
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