OzVMX Forum
Clubroom => Tech Talk => Topic started by: Ji Gantor on September 24, 2008, 09:59:50 am
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I recently removed the forks from my triple clamps so they could be rebuilt. When I reinstalled them everything went well. Out on the track though the forks kept moving up towards the handle bars. I torq the M10 bolts up to the required 25 f/p. I have also tried shimming the forks with 0.05mm brass shims but the forks still move. I purchased another triple clamp in very good condition but the forks move in this set also. Does anyone know of this problem and how to solve it.
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are the threads in the clamps ok?
are the bolts bottoming out (bolts too long) before they tighten up the clamps.
sounds odd since they are original forks and i assume the problem was not there before the rebuild?
measure the OD of forks and ID of clamps!
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It is not the bolts nor there threads. The threaded section in the triple clamps continues all the way through. The OD of the fork outter hard chromed tube is 37.77mm which is what it should be. The ID of the triple clamps is 37.77mm front to back but larger left to right. The aluminium clamp must stretch when bolted up and turns the hole slightly oval shaped. My question is to other Maico restorers that have come across this same problem and found a solutiuon.
Thanks Ji.
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Yes, I replaced the original M10 socket screws with new 12.9 M10 socket screws. I am aware of the ovalizing your are speaking of, yet it sounds much more severe than what I have typically seen on most triple clamps. You indicate 38mm forks ( 75-79 then), and indicate that tubes have been rechromed. Well, 37.7 is what I get on my AW tubes ( original chrome finish). One option is to have the legs knurled in the clamping area. Also, if you make a habit of running a tap through threads, you will , in fact- remove material( especially in aluminum)-use the appropriate thread chaser, as it is somewhat smaller than actual threads size. Still the set I cleaned with a tap held the forks solid .
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I too have replaced the original cap screw but it is not the weak link in the chain. The aluminium thread in the triple clamp will strip before the M10 bolt shears. I do not think there is a device that can knearl hard chrome but I guess you mean abrade the chrome to give it a rough texture. This will provide grip but may prevent the clamp from wrapping around the tube as the pinch bolt is tightened. I have contacted Maico Only and they have informed me that the original fork tubes were 37.77mm diameter. I believe the reseaon the clamps have streched to an oval shape is because other owners have over tightened the pinch bolts. I have been advised to do likewise and tighten them to a torque just below stripping the aluminium threads. As mentioned the clamps front to back are 37.77mm but left to right at there worst point is 38.00mm. This is the same for both sets of triple clamps I have. One set was from a bike here in Australia and the other was a bike from the States. This must be a common problem and I feel some one has solved it short of purchasing a set of after market clamps.
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This may be a long shot . Try using a loctite
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Great suggestion, this was my next move.
Unless someone has any new solutions to my problem, a silver bullet if you will, my next experiment will be to oil the pinch bolts so they will achieve nearly twice the torque as when they are dry. Tighten them to the aluminiums limit and to use a shaft lock locktite. After this I think there are only two options left. The first is to take the triple clamp to an engineer and have him weld them up and then line bore them back to spec. The second is to purchase aftermarket clamps.
Thanks OLD FART
Ji
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Another option is to Helicoil (generic) the clamps as the Helicoil has the effect off reinforcing the original diameter allowing much higher torque and kits such as "Re-Coil" are relatively cheap and easy to get at most engineering and bearing suppliers. Helicoils are a common inclusion in many aircraft castings for additional strength for a given diameter especially in light weight alloys.
Dave Mac
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Just drill out the hole for a through bolt.Then radius the bolt boss near the slit,finally make the gap wider with a slitting saw.It would be better just to machine a new clamp.