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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Tank mounting misalignment
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<blockquote data-quote="davidd" data-source="post: 54500" data-attributes="member: 1177"><p>Ron,</p><p>I spent most of my life trying to avoid exploring details that would have made my life appreciably better, so others like Norman and Trevor, who have years of in depth experience, may have better answers. </p><p></p><p>The bad news is that your FT4 is bent. The good news is that it may not cause too many problems. </p><p></p><p>I spent the winter making two FT4's and I had 5 originals to choose from in order to make the pattern. They were all bent. I chose the least bent and it was .25" off to the right in two feet. I was able to machine the casting so that this deviation disappeared. I concluded that most of the bends were due to sidecar work. The casting just is not designed to take the loads imposed by a sidecar without bending. All were bent between the head lug mount and the steering stem. All of these bikes were US bike and probably should not have done sidecar work, but it could also be minor crash damage. However, if they are all bent, or mostly bent, then it seems that we are not all suffering from disastrous consequences. So, I would not be too upset.</p><p></p><p>I would remove the steering head (the warranty has lapsed, just don't tell Bill) and do some measurements. Your bend looks quite different than what I was seeing. It looks like the twisting was clockwise along the rake axis. The ones I looked at were on a horizontal axis, namely, put the steering stem part in a vice and put a bar through the sidecar lug and jump on it. You may have some of both.</p><p></p><p>You can do some rough measurements on the milling table. I assume you have an "Outy" UFM, that is, the steering lug grips the head lug from the outside and you use the solid head lug. You will have to space the FT4 so that neither the head lug mounts or the gas tank mounts are touching the table. The machined surface you want is the five oil tank mounts, or three mounts with five holes. You will have to take out the bearings. Make some washers to go in the bearing pockets and put a hole in the center to match your ground drill rod. I used 7/8". I used a stop in the chuck and moved the table from one end of the drill rod to the other to see the variation on the quill.</p><p></p><p>I think once you overcome the disappointment you will see that you can do some repairs and get the steering axis somewhere close to the centerline of the five holes. I think this is all you need. you may have to weld and tap an new hole for the gas tank mount, but you will have fixed the geometry already and this would be a cosmetic fix.</p><p></p><p>All of the above is based on the assumption that the gas tank is not strong enough to move that mount hole by itself even in an accident and that the casting has been bent. Once you have it out you can examine it more closely and hope for an easier answer.</p><p></p><p>David</p></blockquote><p></p>
[QUOTE="davidd, post: 54500, member: 1177"] Ron, I spent most of my life trying to avoid exploring details that would have made my life appreciably better, so others like Norman and Trevor, who have years of in depth experience, may have better answers. The bad news is that your FT4 is bent. The good news is that it may not cause too many problems. I spent the winter making two FT4's and I had 5 originals to choose from in order to make the pattern. They were all bent. I chose the least bent and it was .25" off to the right in two feet. I was able to machine the casting so that this deviation disappeared. I concluded that most of the bends were due to sidecar work. The casting just is not designed to take the loads imposed by a sidecar without bending. All were bent between the head lug mount and the steering stem. All of these bikes were US bike and probably should not have done sidecar work, but it could also be minor crash damage. However, if they are all bent, or mostly bent, then it seems that we are not all suffering from disastrous consequences. So, I would not be too upset. I would remove the steering head (the warranty has lapsed, just don't tell Bill) and do some measurements. Your bend looks quite different than what I was seeing. It looks like the twisting was clockwise along the rake axis. The ones I looked at were on a horizontal axis, namely, put the steering stem part in a vice and put a bar through the sidecar lug and jump on it. You may have some of both. You can do some rough measurements on the milling table. I assume you have an "Outy" UFM, that is, the steering lug grips the head lug from the outside and you use the solid head lug. You will have to space the FT4 so that neither the head lug mounts or the gas tank mounts are touching the table. The machined surface you want is the five oil tank mounts, or three mounts with five holes. You will have to take out the bearings. Make some washers to go in the bearing pockets and put a hole in the center to match your ground drill rod. I used 7/8". I used a stop in the chuck and moved the table from one end of the drill rod to the other to see the variation on the quill. I think once you overcome the disappointment you will see that you can do some repairs and get the steering axis somewhere close to the centerline of the five holes. I think this is all you need. you may have to weld and tap an new hole for the gas tank mount, but you will have fixed the geometry already and this would be a cosmetic fix. All of the above is based on the assumption that the gas tank is not strong enough to move that mount hole by itself even in an accident and that the casting has been bent. Once you have it out you can examine it more closely and hope for an easier answer. David [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Tank mounting misalignment
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