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We're building a 50cc vintage race bike over here. Hoping to have it competing for 2016 but also hoping to have it rideable before this winter. Some backstory: Our shop already races a 1972 Honda CB350 in a classic bike roadracing club. Won the championship on it last year. And a 1972 BMW R75 sidecar and a 1958 Triumph Cub 200 and intermittently a 1987 Honda NT650. One of the other guys at the shop, a moped guy, recently got a top tank moped for free, and he was like, "hey man you and I should build something out of this" and I was like, "how about a race bike" and he was like, "yeah awesome." And we bought a 1965 Puch/Sears 4 speed 50 engine off a friend and took it all apart and then discovered it's loving impossible to get parts for and the crank is hosed and then we gave up. But at this point we were kind of committed to the idea of building a race bike. Then one of us remembered we knew a guy with a weird old Yamaha 50 street bike. Bought it off him. Forgot to take a "before" photo. It's one of these:  1982 Yamaha RX50. One of the ugliest bikes ever made. But it's a Yamaha with a 5 speed tranny and a clutch and a disc brake. That pretty much checks all the boxes. It'll be racing in fairly open class, basically it just has to be 50cc and it has to look like what pro 50cc bikes looked like back before 1984 or whenever they vanished. Apparently they never really made this bike to sell, they just produced a few thousand to use as promotional things for dealers to raffle off. Seems kind of pointless to me. Is someone gonna buy an XJ1100 because they got a free ugly tiny piece of poo poo? Got it running. That was a story in itself. Whoever owned the bike previously (not our friend) was some kind of weirdo. They replaced the air filter with a dryer sheet and filled the oil tank with something that didn't quite seem like oil and smelled like lavender. I tried to wash my hands with it, thinking it might be soap if it was perhaps owned by a resourceful but ignorant cleaning lady, but no it's not soap. It fouled the plugs constantly and caused all kinds of problems so one of the first things we did was disconnect the oil injector and run premix. Then we discovered the CDI was misbehaving. When it cranked up the advance above like 3000rpm, it would run something like 100 degrees BTDC instead of the 20 it was supposed to have. Replaced the CDI, it ran great. Thing is a loving blast to ride. Got it on the dyno for a baseline run, it managed around 4hp. We had a pod filter on it and didn't jet it properly for that so it's running lean and probably down on power a little. But hey, top speed 53mph (without wind resistance). Started yanking it all apart, spokes, forks, brakes, tank, seat, bars. We're trying to keep costs down so we're running a lot of parts we already had. 17" moped rims, moped pipe, clubmans, relatively cheap tires (not the $140 dealer cost vintage race Avons). Gonna try to fit the seat from the moped we originally had cause it was a good looking seat. Another guy at the shop bartered expertly with a guy who does fiberglass/carbon fabricating for bikes, so we're basically getting anything we want for it. Probably gonna get a fiberglass tank and a full fairing for it. That's gonna be totally awesome, thought we'd have to save up a couple years to afford that stuff. So here's where it's at right now:  Had to order some custom spokes which we weren't expecting. But all the spokes we had were the wrong size and it looked like a bad idea to lace it up with stuff that didn't fit. The original rims were 16 rear and like 19 front. Weird sizes. It's got a weird design where one of the front forks has a spring and one doesn't. I never liked asymmetric forks like that. Seems like a bad idea. It's got something weird on the swingarm pivots too. Instead of bearings or bronze bushings, it's got rubber bushings in there like the kind you'd put on either end of a shock. When I took the shocks off, the swingarm didn't really wanna move, it sprung back to its neutral position. Because those rubber bushings don't rotate. This is on the swingarm pivot, not the shocks. Another thing I don't get but am not sure how to fix or if I need to fix. Here's more or less what it'll look like when done:  This guy is using the same motor but he has a different custom frame and wheels. Our wheels will be spoke. Can't decide on the paint job. I was originally thinking a Kenny Roberts old style Yamaha design but with red/white/gray instead of yellow/white/black. But now I'm thinking just do the entire thing Ferrari red. Will post more as the work proceeds. Will update this general info chart as work proceeds too: code:Rev. Dr. Moses P. Lester fucked around with this message at 03:19 on Sep 27, 2015 |
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Jun 22, 2015 04:27
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Looking forward to see what it ends up as RevDrMosesPLester. Now the real question is who is going to be the rider?
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Jun 22, 2015 04:48
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Oh man I didn't know I wanted to do this until I saw this. What do you think the rough cost of this project is going to be? What kind of speeds are we talking about once everything is set up?
astrollinthepork fucked around with this message at 05:59 on Jun 22, 2015 |
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Jun 22, 2015 05:57
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Expected to see a YSR in the first picture, only half disappointed. If you are interested, I may have a spare std bore cylinder you guys could port the hell out of.
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Jun 22, 2015 10:28
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Minkee posted:Now the real question is who is going to be the rider? astrollinthepork posted:Oh man I didn't know I wanted to do this until I saw this. What do you think the rough cost of this project is going to be? What kind of speeds are we talking about once everything is set up? As for top speed, we only have vague ideas. Our 350 maxes out at 80 something on that track (NHMS) so I'm thinking maybe 60 something for the 50? It managed a peak of 53 with stock gearing on the dyno so we got a slightly smaller rear sprocket. DefaultPeanut posted:Expected to see a YSR in the first picture, only half disappointed. If you are interested, I may have a spare std bore cylinder you guys could port the hell out of.
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Jun 22, 2015 14:34
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THose welds look terrible
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Jun 23, 2015 01:54
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ought ten posted:THose welds look terrible Yeah did that thing not fall apart and kill everyone after all? Makes me feel better about my lovely welds, if so. Also, this looks awesome.
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Jun 23, 2015 04:14
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Oh man, 50cc race bikes are just the best. We have a motorcycle exhibition run every year at the Copenhagen Historic Grand Prix (no actual racing, because concrete loving hurts), and the 50cc bikes are just crazy. One bike by itself sounds like the angriest chainsaw ever, and a whole field of them is absolutely deafening. And of course there's plenty of smoke  Revving to the moon and having way too many speeds in the gearbox will never get old.
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Jun 23, 2015 14:08
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ought ten posted:THose welds look terrible Called Racetech today, turns out they don't make any gold valves small enough to use in these (27mm) forks. Guess we'll just have to rebuild them with some heavy oil (on the assumption that all 80s Japanese suspensions were too soft) and hope it feels ok. Trying to find out if there's a DuPont paint code for Ferrari red. Probably just gonna paint the whole thing red. Frame, fairing, tank. Might try to make a red vinyl seat cover. Might not, that's kind of a lot of work.
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Jun 24, 2015 01:56
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Rev. Dr. Moses P. Lester posted:We're on year 3 or 4 with that sidecar rig and to date we've not had any issues with the frame. Some engine problems. Over that time we've seen other rigs crack engine cradles and front ends. We actually overbuilt ours, it's too heavy. Yeah I'm just making fun of the concern trolls from back in that build thread. Can't wait to hear this thing ripping around a track. Really like the way that tank and fairing look.
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Jun 24, 2015 04:03
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Our baseline dyno run from before we tore it all apart. Had a pod filter on it instead of the original intake, so it's running a bit too lean. Ignore the big spike at 4500, that was an rpm sensor glitch. Fully full on 4hp there bro.
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Jun 25, 2015 04:03
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What's the margin of error on your dyno? 
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Jun 25, 2015 04:12
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That's the busiest dyno run I've ever seen. Also, yeah, a just a lil' bit lean. 
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Jun 25, 2015 06:22
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Finally, something that makes less power than my Grom. Also, Can't improper mix cause lean condition?
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Jun 25, 2015 09:21
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Yes, too much oil will make it run lean
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Jun 25, 2015 17:23
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I think the mix we had in there was 45/50:1. Either way we're gonna dyno it once it's all together to make sure it's right on with whatever mix we're using.
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Jun 25, 2015 19:21
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Did some parts cleaning today. Scrubbing the engine using degreaser. And a creemee.  Decided to remove the gray paint from most of the aluminum parts with a wire wheel to shine it up. Most of the engine covers, wheel hubs. Looks rad.  24mm flat slide Mikuni and carbon fiber reeds. The original Yamaha intake boot was so well designed we were able to just carve it out with a dremel a bit and it all fits great. 
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Jun 27, 2015 03:16
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What kind/size tires will you be running?
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Jun 27, 2015 10:58
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We got some Hutchinson softish moped tires, 2.75x17. The real tires to get are either Avon non-DOT 18"ers or a similar Heidenau or a Battlax that's only sold through honda for the Dream 50. But all those are like 5x as expensive as the moped tires we got.
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Jun 27, 2015 21:49
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Painted the frame today. Sort of. I wanted a nice Rosso Corsa but the place we usually get paints from couldn't figure out the Glasurit->DuPont for that. Wanted to brush it on because it's such small tubing that a spray would be 90% wasted into the air. Didn't brush on real well, though. Too thin or something. Oh well, it's red. Red is all that matters in racing.
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Jun 28, 2015 01:28
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Maybe it's the camera angle/size of the image but that's pretty impressive quality for a brush job. However uh you're not using the pro-backyard racer choice of Rustoleum so you have negative racing points already.
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Jun 28, 2015 04:32
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We actually had a can of Rustoleum red and I elected not to use it in favor of some expensive DuPont poo poo. Kinda second guessing that choice now. And I drilled some holes in a thing. 
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Jul 1, 2015 03:41
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This is awesome. A dude I worked with used to race some weirdo tiny bikes. 80cc maybe? They were two strokes and he imported them from Italy and apparently they were super fast.
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Jul 1, 2015 08:10
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Don't you have to worry about that sort of drill job causing eventual stress cracks radiating out from the holes? Or would a very slight counter-sink prevent any cracks from spreading. Or am I just overthinking this??
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Jul 1, 2015 08:21
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I didn't think it through much myself, all I know is we did the same thing on another vintage bike disc and it's been fine through a season of racing. I "countersunk" the holes by hand with a small file, in the interests of not chewing up the pads too quickly. Also the bike is so light and slow that I'm assuming there's not really gonna be much stress on that disc.
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Jul 2, 2015 03:46
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Ordered some rearsets. Polished up and rebuilt the forks. Had to guess on how much oil to put in there because you can't get manuals for these things. And laced up the front wheel with a 17" moped rim and custom spokes but haven't trued it yet. It's like 0.080" out axially right now so I was annoyed and stopped there for the day. Wheel bearings are so small they won't fit our normal truing stand axle. 
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Jul 4, 2015 04:12
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Got the front wheel trued to 0.010" axial and i think 0.025" radial although it's a little hard to tell because I couldn't mount it on the truing stand properly because the drat wheel bearings are so small our truing axle won't fit. Did the last bit of chassis painting.  Did a lot more lockwire drilling. That's mostly done now thank god. Updated the OP with a race bike build chart, work to do, parts to get, costs, projected schedule, unknowns. Talked it over with the other guys and decided the rubber shock bushings used as pivots for the swingarm is not acceptable for racing. Gotta punch those out and engineer a proper bronze bushing replacement for them. That could be tough. Rev. Dr. Moses P. Lester fucked around with this message at 04:19 on Jul 6, 2015 |
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Jul 6, 2015 04:13
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Replaced a bunch of the goddamn JIS phillips screws in the engine with allens, installed some of the front end. Sadly it looks to me like those forks are gonna be way too tall, even with the smaller rear wheel. Might have to have them shortened. Disappointing, because if it weren't for that, I think we'd have spent our last major dollar on this bike already and it would be just labor from here. Punched out the stupid rubber bushings from the swingarm, took a lot more work than I would have thought. Gotta find some bronze poo poo and have them machined to fit now.
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Jul 9, 2015 02:42
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What's wrong with just sliding the forks up in the triples like crazy? As long as you don't lift them so high they bottom under braking whatever. Put a chin rest on the top of them if they're like 18 inches up.
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Jul 9, 2015 06:42
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Problem is the top triples are not clamp-type triples, they're moped style where the fork cap bolt holds the fork and triple together. The fork can't slide through them. Top triple is just a stamped piece of flat steel. I'd like to keep the front end because it already has a good caliper and disc and etc. on it, and i dunno what other options there are besides customizing the forks or customizing the top triple maybe.
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Jul 9, 2015 19:30
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Rev. Dr. Moses P. Lester posted:Problem is the top triples are not clamp-type triples, they're moped style where the fork cap bolt holds the fork and triple together. The fork can't slide through them. Top triple is just a stamped piece of flat steel. I'd like to keep the front end because it already has a good caliper and disc and etc. on it, and i dunno what other options there are besides customizing the forks or customizing the top triple maybe. Ahh, that's unfortunate - I'd want to be able to customize the front ride height as well, a little change there goes a long ways.
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Jul 10, 2015 00:22
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Did you do the rear wheel as well? Maybe when you have both tires on it won't look so bad.
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Jul 10, 2015 00:30
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Made the rear wheel bigger and the front wheel smaller, but I'm pretty sure that front end is just too high. We came up with a solution, we're thinking about buying another steering stem for that bike (like $20 on ebay) and cutting the pinch clamps off it and welding them onto our upper triples. Then simply adjust fork height as normal. Got the rear wheel all together with tire on it now, removed all the wiring we don't want. Gotta take the swingarm to a machinist and see about having some bushings made and get a bunch of m6 allens from Fastenal next.
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Jul 10, 2015 02:45
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I'm kind of curious about the exhaust - are you going to take an existing 50cc exhaust setup and cut-and-weld it back together to fit it on the bike, or are you going to fab up your own solution? I'm kind impressed to see that those 50cc tuning pipes exist and look like they're made pretty well, although they're expensive. Also why the hell did Yamaha make the bike's front forks so hilariously tall? Looking at the stock bike photos it almost looks like they were saying to themselves "hey, Americans love cruisers, so let's make a cruiser out of a 50cc 2-stroke bike" which anyone with 3 brain cells would've called "a hilariously lovely idea" but yeah.
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Jul 18, 2015 18:02
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Every Japanese maker did that in the early 80s. Every single bike was a cruiser. It was a horrible time to be alive. As for the pipe, we were intending to do a minimal welding job to fit a standard 50cc moped tuned pipe on it. The pipe we had, though, turns out to be totally the wrong shape, and it looks like it'll get a lot more complicated than that. Not sure what we'll have to do. Waiting on the machinist to do the custom swingarm bushings at the moment. Once the bike is mostly together, with both wheels and rearsets installed, then we'll need to see how we can fit an exhaust on it. I've heard you can buy kits to weld together your own cones and whatnot for 2t exhausts, we may have to do that I suppose.
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Jul 18, 2015 20:37
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Yeah after the 70's everyone went completely batshit for cruisers apparently and every bike got a "custom" model that got what was invariable the worlds worst king/queen seat, a knockoff Harley teardrop tank and FUCKEN RAKE MAN. Dark times indeed. The worst of it all is they were so popular it can be hard to find the non "custom" versions of some bikes. I call them softball cruisers. 80's faux cruisers you invariably see parked at a softball game.
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Jul 18, 2015 22:58
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Ha, I remember as a kid thinking Yamaha Midnight Specials were the poo poo. Then they came out with the FZ's and the Vmax and it was like the gates of Valhalla opening
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Jul 19, 2015 04:47
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How the gently caress did I miss this thread? Awesome.
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Jul 19, 2015 06:34
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Put those fantastic welding skills to use, pull out the power washer and hydroform for own pipe! 
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Jul 21, 2015 00:50
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Holy poo poo is that for real?
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Jul 21, 2015 04:29
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