michaelmoore Posted September 7, 2008 Report Share Posted September 7, 2008 Can anyone comment on how well the front and rear rims should line up with each other and the center axis of the bike? The front rim is centered in the forks. I've set the rear axle so it is pretty well parallel to the swing arm pivot spindle, and that gives me good alignment on the front and rear sprockets (with a long straight edge held across them). But I've got the drum (left) side spokes on the rear wheel almost bottomed out, and the right side spokes without a lot of engagement in the nipples, and it looks like I've still got to move the rim over another 6-8mm to the left, and that's just not going to happen with this spoke set. The left sides of the rims are pretty much in plane with each other. The rims are nominally 2.15 and 1.6" which means the front rim needs to go over a bit more than 1/4" inch. Some bikes, like the early Z1 Kawasakis, came from the factory with the wheels offset. It probably isn't as critical on a trials bike as it would be for a roadracer but I'm not wild about that idea. However, if that is the way the Sherpa T's normally run then I'll just pull the rim over as far as I can and try to not worry about them being out of alignment with each other. FWIW, I'm not seeing any obvious signs of the frame being bent, but I haven't taken it back apart and put it on my frame fixture to check it. I've been hoping that I'd eventually get to the point where this thing would be going back together without finding another stumbling block in the process. cheers, Michael Quote Link to comment Share on other sites More sharing options...
bultaco49 Posted September 8, 2008 Report Share Posted September 8, 2008 Hi Michael When I read your qustions on here and on the yahoo sherpa forum it warms the cockles of my heart that someone puts so much effort into their engineering. If only Bultaco had too! I have never managed to get wheel alingment perfect on a used sherpa (including my model 158). I've neve owned a new one to know wether they were any better. I suspect not. My method is to lace up the new wheel so the rim is centred and concentric and then fit it to the bike. The exhaust, chain tensioner and chain guard must be fitted. I then align the sprockets & chain then simply adjust the spokes so the tyre is aligned in the swingarm and fouls niether the chainguard or exhaust. Fitted with a modern tyre this is a tight fit! (be prepared to hook out mud and leaves from swing arm base area and chain tensioner between sections). Many Sherpa's have no paint and occasionaly wear holes through the clubfoot spark arrestor because of the close fit to tyre. Ditto wear to chain guard. Always clear the mud & debris away from the chain tensioner as this gets pushed sideways and will take off the chain and the snap the rear magneto case mount off and rip a piece of alloy out of the crakcase. Tim Quote Link to comment Share on other sites More sharing options...
toofasttim Posted September 8, 2008 Report Share Posted September 8, 2008 Some bikes, like the early Z1 Kawasakis, came from the factory with the wheels offset. That probably wasn't by design. No wonder the things didn't handle. Quote Link to comment Share on other sites More sharing options...
nigel dabster Posted September 8, 2008 Report Share Posted September 8, 2008 Hi MichaelWhen I read your qustions on here and on the yahoo sherpa forum it warms the cockles of my heart that someone puts so much effort into their engineering. If only Bultaco had too! I have never managed to get wheel alingment perfect on a used sherpa (including my model 158). I've neve owned a new one to know wether they were any better. I suspect not. My method is to lace up the new wheel so the rim is centred and concentric and then fit it to the bike. The exhaust, chain tensioner and chain guard must be fitted. I then align the sprockets & chain then simply adjust the spokes so the tyre is aligned in the swingarm and fouls niether the chainguard or exhaust. Fitted with a modern tyre this is a tight fit! (be prepared to hook out mud and leaves from swing arm base area and chain tensioner between sections). Many Sherpa's have no paint and occasionaly wear holes through the clubfoot spark arrestor because of the close fit to tyre. Ditto wear to chain guard. Always clear the mud & debris away from the chain tensioner as this gets pushed sideways and will take off the chain and the snap the rear magneto case mount off and rip a piece of alloy out of the crakcase. Tim For the clubfoot silencer fit a big spacer and get the flange outside the frame plate. Moves the thing away from the tyre. Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted September 8, 2008 Author Report Share Posted September 8, 2008 Hi Tim and Nigel D. I'll try to remember to attend to the silencer. I can't bring myself to ride it when there are so many things that need attention. I didn't anticipate quite this level of renovation being needed. I'd hoped it would be a "new chains/sprockets/steering bearings/tires now let's go ride" kind of fix up. I've cleared the frame fixture and so far I've determined that the swing arm is twisted. Looking from the back, over a distance of 6.7" the right side of the rear axle is .252" higher than the left. The swing arm doesn't seem to be bent sideways though, only twisted. I don't know if I can securely clamp the swing arm to the base of the fixture so I can try and pry on it. I'll have to give it a try. I'm not going to be too surprised if it doesn't take a lot of effort to move the swing arm. There are a lot of vintage bikes where you can grab the top of the tire and pull and watch the swing arm flex. The front axle doesn't seem to be in the same plane as the swing arm pivot when the two spindles are parallel (ie, the forks want to be turned a little to the side to get the axle to lay flat). I'll get the bare frame up on the frame fixture this afternoon and see if it is just the frame, the forks, or a combo of the two. I'm really hoping this doesn't get to the point where it seems easier to build a new frame and/or swing arm. cheers, Michael Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted September 8, 2008 Author Report Share Posted September 8, 2008 Quote Link to comment Share on other sites More sharing options...
02-apr Posted September 8, 2008 Report Share Posted September 8, 2008 Sammy Miller went in to print at the time to say that a trials bike with the wheels offset was easier to balance so, leaving Bultaco build quality out of it, they weren't meant to line up in the first place. As for Z1s a friend had one of the first and the ride home from Lancashire after collecting it was very interesting - no bushes in the swingarm bearings. Handling was later cured once and for all by fitment of a Harris frame. Quote Link to comment Share on other sites More sharing options...
swooshdave Posted September 8, 2008 Report Share Posted September 8, 2008 Sammy Miller went in to print at the time to say that a trials bike with the wheels offset was easier to balance so, leaving Bultaco build quality out of it, they weren't meant to line up in the first place. That actually makes sense. Quote Link to comment Share on other sites More sharing options...
bultaco49 Posted September 8, 2008 Report Share Posted September 8, 2008 Hi Michael Just did a brief scientific 'lean on' test on my model 221 (similar swing arm) and yes, it does flex quite easily. The lift on your swing arm is on the leg on which the side stand is attached. I was told off by and old Bultaco sage at a trial for leaning on my bike while it was on the side stand It will 'bend the swing arm' he scowled..... Later model Sherpa's have a rib along the topside of each leg to check this deflection and Comerfords 199bs have a square section. I'm not sure what steel Bultaco frames are made of (old buiscuit tins if the rumours are true) but it has no where near the torsional qualities of regular framemakers high spec steel tube such as reynolds 531 etc. For most years of their production good tube was embargoed and unavalable for production. Sammy Miller frames are made of 531 and had a considerable tensional and weight advantage increased by having alloys available for structural bash plates. My point being that I don't think the steel will be so highly strung that some heat and an equal and opposite force (to that which twisted it) might be the answer to your twisted swing arm. Tim Quote Link to comment Share on other sites More sharing options...
swooshdave Posted September 8, 2008 Report Share Posted September 8, 2008 For some reason I want to say that Bultaco went to the better steel around the Model 158 timeline. But I could be wrong. I will say that the side stands must bend easily as the ones on both my Sherpas are "not straight". I don't know why anyone would put any load on a bike when it's on the side stand. At least the kickstarter is situated that you would be hard pressed to start the bike whilst it was on the side stand. Although I wouldn't put it past an enthusiastic owner... I always cringe when I see big Brit bike owners starting the bike on the side stand. Quote Link to comment Share on other sites More sharing options...
bultaco49 Posted September 8, 2008 Report Share Posted September 8, 2008 Until 1975 steel tubing for Bultaco's had to be sourced in Spain as during Franco's rule there were sanctions against Spain. Even though Franco died in 75 and Spain began a transiton to a democracy and high grade imported steel tubing became available it was never used on production Bultaco frames. Though it was better quality the tube was still sourced and produced in Spain. Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted September 8, 2008 Author Report Share Posted September 8, 2008 I've gotten it down to about .025" over the 6.7". With my crude levers and clamps I managed to overbend once so I decided that getting 90% of it out was going to have to be close enough. Another couple of big Kant-Twist clamps need to be on the shopping list. C-clamps just swivel and gyrate around when trying to use them to clamp objects while they are moving. It did take a pretty fair bit of movement for things to start bending and staying bent. It seems like the axles will now lay in the same plane and parallel, but the triple clamps look to be a little off to one side. I've not got those clamped up with the pinch bolts but I did use the top caps to pull them into the top clamp. I'll try loosening the top caps and see if I can twist things a bit there. If that doesn't work, then the top clamp will have to come off while I look at that area. The righthand gusset at the steering head shows a little bulge in the middle of the back edge, which could just be from being hit by something at some time, or due to a bit of movement between the top and front tubes causing it to buckle. I've seen that same problem on some other frames that lack triangulation of the steering head and count on the gussets to stiffen things up. Putting a little bit of a right angle rib on the outside (open) edge of the gusset would help it resist that kind of distortion. Since all the steels have the same modulus of elasticity they are all equally stiff. Using 531/4130 vs mild steel with all the tube sizes the same gets you a frame of equal stiffness, but one that will bend a bit farther before taking a permanent set. I've seen mention (Morley?) of works riders from the UK taking lengths of 531 in their luggage when going to Spain so that it could be used in their personal bikes. Where the Bultaco has a 28mm round swing arm the KT250 has a 28x 36 ellipitical tube. Top tubes are the same OD at 36mm and the subframes are 20mm vs 3/4". Bultaco could have gone to a 44 x 1.5mm top tube, saved 6% in weight and increased stiffness by 50%. That could be carried through on the rest of the frame. I've seen triangulated space frames on roadracers that were lighter than trials frames and immensely stiffer in both bending and torsion. I guess it took a few more years before the trials frames designers started doing something other than the same thing they (or someone else) had been doing for 20 years. Oh yes, the side stand needs some attention as it is pretty bent up, probably from someone doing what Dave describes, standing and starting the bike while it was leaning on the stand. Back to the garage to look at the forks and clamps! cheers, Michael Quote Link to comment Share on other sites More sharing options...
mickwren Posted September 9, 2008 Report Share Posted September 9, 2008 I really can't believe that so many people have taken this so seriously. If it's only 6 to 8 mm out of line thats pretty accurate for a spanish trials bike of that era Quote Link to comment Share on other sites More sharing options...
swooshdave Posted September 9, 2008 Report Share Posted September 9, 2008 I really can't believe that so many people have taken this so seriously. If it's only 6 to 8 mm out of line thats pretty accurate for a spanish trials bike of that era Well, there is two ways to think about it. Do you want it as good as it came from the factory or do you want it better? It not like folks with modern trials bike don't modify theirs. Quote Link to comment Share on other sites More sharing options...
02-apr Posted September 9, 2008 Report Share Posted September 9, 2008 I really can't believe that so many people have taken this so seriously. If it's only 6 to 8 mm out of line thats pretty accurate for a spanish trials bike of that era I can't help but agree - we didn't bother doing anything about it in the day but a pal did have to resort to the sophistication of a scaffold tube to straighten out his blue Sherpa when it went end over end at about 30. Quite impressive from behind as it went for a good way on the front wheel with his hands on the mudguard before flipping over. Quote Link to comment Share on other sites More sharing options...
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