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« on: 31 October 2020, 03:09:15 pm »
Thanks for your inputs so far. I like the bike and want to see it back on the road rather than broken for parts, if the frame is okay the only expensive bit will be new forks anyway; I think I can save the body parts.
The paint around the headstock tube welds is flaking off... as it was when I bought the bike. At the time I attributed it to rust, but I wonder if it had a crash before I bought it, especially considering one of the forks was (slightly) bent when I rebuilt them earlier in the year. Bodywork was immaculate at the time, so a crash seemed unlikely.
I've strung a line from the shaft that runs through the yokes and headstock bearings to a crossmember with a series of holes drilled through it under the seat. To the best of my ability to measure, at that crossmember and the two above the engine, the string is perfectly centered in the frame. I'm not too confident in my measurement where it passed over the fuel tank fixing hole at the front, which appeared to be ~2mm to the right, I'm not sure if that hole necessarily *should* be centered anyway.
I've not been able to find any good articles on frame geometry, but to my thinking, I've got these possible ways the frame could be distorted by a crash:
Lateral twisting
Lateral twisting of the frame, skewing the angle the steering will rotate around to the sides, moving the wheels out of line and also altering the tyres' contact patches. Will probably make it want to wander or prefer one direction, like when the rear wheel is misaligned.
Bending to the left/right
Sideways bending of the frame, without the above latteral twisting, moving the wheels out of line but not affecting the tyres' contact patches. I don't *think* this would impact the handling much, assuming the rear wheel alignment is adjusted to compensate?
Bending up/down
Bending up/down, or the frame being squashed shorter, moving the front wheel rearwards by reducing the steering rake angle. I think this would actually give it slightly sharper/sportier turning, but otherwise not impact the handling?
Obviously any distortion to the point that a weld is damaged is dangerous. I will do DPI testing of critical/stressed welds (i.e. the ones at the headstock tube).
I bought a digital inclinometer, intending to use it to rule out lateral twisting of the frame between the swingarm mounting uprights and the centerline of the yoke shaft, but I haven't come up with a way to get a reliable reading off of the latter yet.
Does my above thinking seem correct?
Thanks all