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Discussion Starter #443 (Edited)
Well, the problem child continues to present me with problems. The idea of just "taking a bit off the face" of the sprocket carrier to move the stock ID sprocket toward the centerline turned out to be unworkable; the wall thickness of the carrier casting just isn't thick enough to do that. So, I came up with an alternative. The diameter of the carrier behind the sprocket location was ≅105 mm. I went looking for a sprocket with an ID just very slightly less than this. I found it in a sprocket for late '90s and early '00s Ducatis. (Unlike the OE sprocket from the GS450T, which was 530, this would match my Bultaco's 520 countershaft sprocket.)



A little lathe work would give me the ability to mount the Ducati sprocket behind and flush with the stock sprocket location. I could then cut down the stock sprocket, turning it into a secondary sprocket carrier.

I drew up a profile of the carrier casting in section at its thinnest point, to ensure that I wouldn't end up removing too much material. As it turned out, I wouldn't be removing material from any of the thinnest portions of the casting.



That would allow me to mount the sprocket, but how to bolt it in place? That's where the OE Suzuki sprocket came into play. I could cut the perimeter off and turn just the center and spokes into an outer "spider" that would locate the Duc sprocket securely, and give me something it could bolt to from behind.



Unlike the aftermarket JT GS300 sprocket I had been intending to use, the stock GS450T is really thick, with wide spokes, and made of unbelievably tough steel. Cutting it down with my recip saw and turning the spokes on my lathe were challenging, but eventually I had it shaped.

Compared to the sprocket, turning the alloy Suzuki carrier was a piece of cake.



Even though I still need to drill the outer holes in the spokes of the old sprocket for the Duc sprocket to bolt to, I had to assemble it all on the bike and check my handiwork. The chain run lines up perfectly, and even though it looks a bit odd, this arrangement will be strong and safe.

 

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Discussion Starter #448
I got the sprocket carrier drilled. I scribed out the locations and created a somewhat rinky-dink jig setup to drill the holes as accurately as I could. I checked each hole after drilling. Five were spot-on; one needed a tiny bit of grinding and filing. once I bolted it up, I temporarily wrapped the chain around it to see what I had. The chain run is arrow straight. Looking at how the chain runs through the frame components, there were no rude surprises, and everything seems in order.

I'm happy at the progress lately. At this rate, the lack of a functional engine will soon be somewhat conspicuous.









 

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Discussion Starter #450
Moving on to the next task: pegs and foot controls. Playing around with a set of Yamaha YZF600R footpegs and pedals as my starting point, all the configurations I came up with were deficient to some degree, both functionally and aesthetically. I have some additional parts on the way that will allow a more elegant solution while at the same time improving the crappy swingarm pivot support on the right side of the frame--something I did early on that has been bugging me more and more. Stay tuned.



 

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Discussion Starter #451
One of the first things I did, 8-1/2 years ago, was mount the swingarm. I was originally trying to build the bike with no machining or welding capabilities, so I made some fairly ignorant decisions. One was the left-side swingarm mount. I had a 12 mm axle located in a 14 mm hole. I used a jinky arrangement with a sheet metal escutcheon plate and some 6 mm socket head bolts — it was a wholly unsatisfactory arrangement. So, while figuring out how to mount the pegs and foot controls, I decided to remedy the situation. I turned a brass reducing collar on the lathe to properly center the pivot bolt.





I then replaced the 6 mm spacers between the frame and engine mount side plates with triangular steel plates of equal thickness. I bought 7 of them off Ebay for $10, and they came with two pre-drilled holes on the wide end. I drilled an additional hole for the swingarm pivot directly between them (15 mm for the right side, 12 mm on the left). This is a nice snug fit, and when these are bolted to the frame from inside, they will add additional support for the swingarm bolt while simultaneously giving me a more tucked-in mounting point for the footpegs.




Finally, speaking of tucking things in, I needed to create clearance for the kickstart arm. I am grafting together the bottom of a Bultaco kicker, with the proper splined mounting hole, with the upper part of a Honda ATC250R kickstarter, which is angled to swing out much farther away from the side of the bike when extended. These will be machined to fit together, then welded.




I rolled it outside briefly and took a picture of its current status, to keep me motivated and record my progress.

 

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Discussion Starter #452
I made some progress on my kickstarter modification.
When I took the earlier photos above, I had already chopped the lower clamp off the ATC250R kickstarter. The next step was to turn down the Bultaco kickstarter arm to a 10 mm diameter shaft.



I then bored a 10 mm hole all the way through the base part of the Honda kickstarter and pressed the two parts together. Given my lack of machinist training, I was happy to nail an easy but tight press fit.



I still have some steps to complete. I still need to weld the two parts together, which I will do both at the top and bottom of the shaft, and I need to re-drill the hole in the side for the detent ball and spring.



It's not exactly pretty, but it will work! Now I can continue with fabricating the footpegs and pedals.

 
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