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Home Forums Sidecars Sidecar Builds R75/6 sidecar subframe RE: R75/6 sidecar subframe

#5823

Coriman
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  • Rank: 125cc Rider

Picture of the Rear bolt on frame, which is very weak for a sidecar and not recommended without additional strengthening.
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I fabricated an under seat sub frame to stiffen the top of the rear suspension units. You lose the tool tray but gain a sidecar.
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The frame was cut from 50×50 angle and fully welded but do not weld to frame use high tensile bolts. Cap screws are the strongest.
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The top suspension bolts are substituted with long cap screw which pass through the units and right trough the fabricated box section, which have internal side wall bracing tubes, so you can fully torque the fastenings without crushing the box section.
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The bolts in the picture are low grade just for temp jigging the job. I will post more info later.
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To continue, as this was prototype work minor fitting mods happen during the build but here is the first stage in place. It does not impact the seat, and is above the battery box, which needs to be installed prior to the rear mudguard .
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The lower engine mounted sub frame is cut from 10mm plate, and held in place by the engine mounting bolts. Cutouts are made for the gear lever and frame tubes. This plate goes behind the exhaust so this can be moved out at the rear clamp by 10mm for clearance.
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The bottom plate carries both front and rear sidecar mounts, and the tail is extended up behind the muffler at an angle, then another fabricated plate is welded to that , which mimics the passenger footrest plate on the bike.
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The front of the plate is fabricated into an open box section for strength. and the sidecar mounting bosses are bolted on front and rear.There is and addition diagonal under brace which attaches the rear of the lower plate to the opposite side lower bike frame member.
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On the last picture on this page you can see the lower plate fitted with the rear lower side car attachment boss which take the standard sidecar threaded fittings. Also note how the plate wraps around behind the muffler and the strengthens the passenger footrest plate. The foot rest then locates both.
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I have added another frame tube outside and parallell to the original, which is bolted to the top of frame and suspension unit , and again bolted with high strength cap screw to the bottom plate to give torsional rigidity, since the original frame pate is the thickness of your little finger. Ok for solo just , but no good for side car forces.
I will tell more on another post. Note Do not weld onto the bike frame itself.