Quote:
Originally Posted by blackiredi
My question is, is the recessed part where the threads are hollow? If so has anyone cut the whole jimmy out and replaced it with a piece of plate steel? I would prefer to do this method because I can get the same strength and recess the peg more so it doesn't touch down as much. Curious if it's been done and if there are pictures?
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Rearset mounting of frame is same as surrounding area, dual-wall hollow box-section. By connecting both outside and layers, you get maximum strength for least amount of weight and material used. Look at how mounting for swingarm pivot is configured. The wider the inner to outer surface that’s connected, the stiffer and stronger the joint.
“Issue” with rearset mounting is that actual contact area (threaded nuts) is only on outer surface of frame. This has strength and rigidity of only 1.8mm layer rather than 30mm width of swingarm pivot mount. This is actually by design, here’s how it looks on unused back side.
I had factory mounting point bend inwards enough that rearset rubbed on swingarm after crash on my 1st race-bike. Not wanting to have it occur again, I welded in ½” steel plate with threaded holes for rearset similar to what’s shown earlier in this and other threads. Problem with this method is it doesn’t decrease forces on mounting-point in crash.
Rather than bending or stripping out mounting point, that impact force is now transferred further forward on frame… and bends frame there instead… at swingarm pivot!!! This happened to my frame at next crash. Wasn’t obvious at first, because rearsets were fine, but suspension behaved weirdly. It compressed more than before and rebounded less, sometimes bottoming out. Movement was also slow and lazy. Asked Dave Moss to take a look and he said it felt like suspension bearings were dry and needed greasing… odd I had done that just 5-months ago…
After taking shock and linkage off, I couldn’t even move swingarm up & down! Needs grease! So I pulled out pivot-axle, clean and greased needle-bearings and reinserted axle…. It didn’t fit!, tip ended off my about 1mm on other side. If I bent and forced axle through 2nd hole, it bound up bearings so much, swingarm couldn’t swing! I had bent my frame in crash because rearset mounting was TOO stiff, and forces from crash leveraged off rearset pegs and bent area ahead of rearset mounting, the swingarm pivot!!! After close to $1000 from GP Frame, I got frame back, un-bent and re-aligned so swingarm bolt can go straight across.
On my 2nd race-bike, I used solution provided here:
https://www.ninjette.org/forums/showthread.php?t=340674
Connect both outside and inner-layers (I spot-welded thin nuts on outside of inner frame-surface). By loading bolt in double-shear, you get stronger mounting point. To reduce forces imparted to frame during crash, I replaced solid pegs that came with rearset with folding pegs. Along with using hollow aluminium bolts to attach rearset to frame. This further reduced forces on frame in crash as rearset broke free rather than bending frame. I safety-wired rearset to frame so it wouldn’t get lost when breaking off. I shared this solution with another racer who had swingarm-pivot bend in crash because of re-inforcing rearset mount after prior crash. After 2 additional crashes on mine and 3 on hers, neither of our frames were bent at swingarm pivot!
BTW - frame is made of mild-steel, 1020 or 1022. Not aluminium as mentioned earlier in this thread. Not sure how welder was able to weld aluminium spacers to steel frame. Ferrari has patented process "Ferran" to attach steel to aluminium. Suppose it's some kind of brazing using custom filler-metal that adheres to both. Certainly not something welder in San Jose did.