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Looks fairly simple. https://www.youtube.com/watch?v=ppXRMTeR2NQ
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Jul 21, 2015 04:36
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Also not as dangerous as you might think. Water won't compress enough to create the type of pressure that turns your pipe into a grenade, it just starts springing leaks.
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Jul 21, 2015 05:36
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My reading on the topic suggests you need to be very precise with the taper angle and length of the cones on your pipe though. It's not just "big here little there ok throw it on the bike." I wonder how hard that is to get right with that technique.
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Jul 21, 2015 18:01
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I think the toughest part is getting the welds to lay flat. I think the big guys crimp the edge of their plates to a 90* angle to that they can weld there edges flat before expanding with a water/oil mix. Not sure why they use that, though. Either way, your circumference should end up being the same blown up as it is flat.
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Jul 23, 2015 15:23
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Would the tapers be the same though? If I welded a certain angle and then blew it up, the angle in the resulting cone would be the same? That seems like the important part. I don't know enough of "the physics" to know how that works. We're thinking about buying an aftermarket moped expansion chamber and welding it to what's left of the original exhaust pipe. Anyway I was on vacation for a bit and we had to wait a while for a machinist to make some custom swingarm bushings so not much happened for a while. But we got the swingarm in, top triple trees modified, forks slid up, wheels on, shocks on. Decided to go with 1" taller shocks from a moped. Was a pain in the rear end to make the shock bushing eyelets fit the unusually large Yamaha shock posts.  We have a custom made fairing lying around waiting to be mounted on a 1958 Triumph Cub 200 race bike, so we threw it on the 50 to see how it would look. I think the fairing was originally designed to fit a Bultaco of some kind.   It doesn't quite fit but it's close. The steering neck is a bit far forward on the bike and of course the bars aren't really in the right spot. We may need to get some clipons, but hope not. Gonna talk to the guy who custom makes these fairings and see if he can mod the front end of it a bit. Make it taller to fir the bars and a bit of a cutout more forward to make space for the forks. And I'd like a more rounded torpedo shaped nose rather than the sort of smushed style this one has.
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Aug 14, 2015 05:45
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Attached some spools to the swingarm today. Made a rear stand for it out of a scrap scooter centerstand and scrap chrome barstool legs. Still needs a little modding. Needs a brace bar on the bottom to keep it from rolling over backwards when taking the bike off it, and needs some cutting on the left side because it's blocking the rear axle in, and needs a lot of filing and grinding to round off sharp edges. Could probably shorten that handle a lot too. 
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Aug 18, 2015 01:37
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Got the rearsets mostly on, duct taped an expansion chamber on and spent a couple days on the dyno. It didn't go that well. We think our carb is too big (24mm). Stock was like 16, and after loving with everything that can be hosed with in the carb, there's still all kinds of things going wrong with the mixture in the low/mid range. And the peak WHP is no higher than it was when stock (4.3). Also thinking our test pipe may not be good but unsure of how it ought to be different and it's quite a project to try another one. Basically involves finding another moped pipe of some kind, chopping it all up so it kind of mates with the stub header from the original pipe, and then dyno tuning to see what happens. Anyway, here's a video of it not running the way I want. https://www.youtube.com/watch?v=XwYh1rwMCEQ
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Sep 1, 2015 04:04
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Wowzers, 24mm seems massive for an engine that tiny.
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Sep 1, 2015 07:24
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Yeah I mean you would have to have the thing massively ported to flow even close to the air a 24mm carb can flow
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Sep 1, 2015 21:40
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I picked it because I saw another guy at the track with the same engine and he had that same carb on it. Also it's a flatslide and it looks awesome. But today I went back to the original (~17mm) on it and peak hp was exactly the same and the low end was much better. Only problem is that carb is almost impossible to tune, it has jets I've never seen before and can't find in any of our catalogs. I wanna try a more aggressive pipe but thinking we may need to buy a proper performance carb in the 18mm range too.
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Sep 2, 2015 03:43
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Rev. Dr. Moses P. Lester posted:I picked it because I saw another guy at the track with the same engine and he had that same carb on it. Also it's a flatslide and it looks awesome. But today I went back to the original (~17mm) on it and peak hp was exactly the same and the low end was much better. Only problem is that carb is almost impossible to tune, it has jets I've never seen before and can't find in any of our catalogs. I wanna try a more aggressive pipe but thinking we may need to buy a proper performance carb in the 18mm range too. Wouldn't an 18mm off something like my 100 be enough for your purposes? With different jetting of course. I can't imagine your build will be so insanely powerful that you need a carb bigger than an engine twice the size has. Or are you specifically attached to the idea of a flat slide?
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Sep 2, 2015 04:11
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I just mean I need something that was made recently and uses standard performance jets and needles. The jets in the Mikuni TM24 flatslide we had on it were literally the same as the ones we have in our 38mm round slide Mikunis on our sidecar rig.
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Sep 2, 2015 19:32
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Go with a vm18. It will still be a non-cv carb, which is half the battle, and it will use commonly available parts
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Sep 3, 2015 02:27
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I have a Dellorto PHBG 21 on my 70cc reed valve engine. 19mm PHBGs seem to be popular on 50s.
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Sep 3, 2015 03:00
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Yeah we were looking at both VMs and PHBGs. Did I hear that the Dellortos have a 3 jet system? I like the sound of that. Unless maybe there are a wider range of needles available for the VMs. The TM24 we had could only get one needle jet and only 2 needles.
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Sep 3, 2015 19:11
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Nope. The PHBG only has two jets. But a zillion different sizes of each as well as different needles/slides/floats.
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Sep 4, 2015 05:45
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I'm an EFI idiot so I'm lost in the carb chat here, but I just wanted to say the dyno video is everything I wanted it to be. 
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Sep 5, 2015 01:09
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Had a drag race today against a Buddy 50 scooter with a Prima pipe. (it's a p. fast scooter if you're not aware, bro) I won. So I'm feeling optimistic. Bought a copy of this thing http://www.buildandclick.com/html/tuned_pipe.html and ran the numbers on it. It came up with a pipe that seems surprisingly not that aggressive. Meaning the width of the expansion chamber at its widest is not nearly as wide as the Prima pipe on the above mentioned scooter. I thought that was kinda funny. From the reading I've done, it sounded like for peak HP you'd want a diffuser cone with a wide outlet and a baffle cone with a sharp taper. Maybe it depends on port timings which I assume are rather conservative on this bike. But I'm thinking about trying the hydroforming technique on the software's prescribed pipe this winter.
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Sep 5, 2015 03:43
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That program looks absolutely fantastic.
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Sep 5, 2015 04:22
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Rev. Dr. Moses P. Lester posted:Had a drag race today against a Buddy 50 scooter with a Prima pipe. (it's a p. fast scooter if you're not aware, bro) I won. So I'm feeling optimistic. Is the Prima Buddy pipe a true expansion chamber? I know in the Vespa world a lot of "performance pipes" are actually baffled inside. I'm not sure if that holds for the Prima Vespa/Stella pipe (but I do know that pipe is not well-regarded).
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Sep 7, 2015 05:01
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Gay Nudist Dad posted:Is the Prima Buddy pipe a true expansion chamber? I know in the Vespa world a lot of "performance pipes" are actually baffled inside. I'm not sure if that holds for the Prima Vespa/Stella pipe (but I do know that pipe is not well-regarded). They have these on a lot of street legal scooter exhausts but they're usually extremely easy to remove. I had a look at some of the Vespa pipes and it looks like you have to cut the thing open to get them out?  
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Sep 7, 2015 09:32
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open24hours posted:They have these on a lot of street legal scooter exhausts but they're usually extremely easy to remove. I had a look at some of the Vespa pipes and it looks like you have to cut the thing open to get them out? I don't know anybody that has done that, everyone just goes for a better pipe. There are a lot of true expansion chambers out there for Vespas. We don't have to deal with inspections or anything, though.
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Sep 7, 2015 22:09
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Good lord I had no idea such awful things were out there. I don't know for sure about the Prima pipe but it does have a repackable muffler at the end of it and it has PRO LEVEL looking welds all over the cones on it so it might be legit. So this last Monday we had the rx50 out for the first time on the track. I don't think I got any good pictures of it at all, sadly. Here's a bad one:  Sadly it looks like poo poo right now because: 1) still no fairing 2) still using the original hideous tank 3) the seat we had needs a lot more modding than expected, and the subframe too 4) same with belly pan and exhaust too maybe because we can't fit the belly pan under it yet Good news was it was doing ok on the track, passed tech inspection, didn't blow up, was kinda keeping up with other bikes in its class. Bad news was it turns out the rear brake was adjusted such that it was dragging in just the tiniest possible way and after 2-3 laps it would heat all the poo poo up back there and start to drag quite a bit more. Every little bit hurts on an engine that size, so it was noticeably down on speed. I never even used the rear brake except on the dyno, so I didn't think to check it for problems. Gonna regear it for the last race of the season which is on a faster track, and then think about mods over the winter. Clipons, custom exhaust, porting, port/case matching, maybe messing with the head to raise compression, a better (but not too big) carb, maybe a swingarm brace, and of course the bodywork. I'm also wondering if it would be worth the expense and effort to get ceramic or ceramic hybrid bearings for the engine and wheels, since noticing how every little bit of friction matters after the rear brake incident. And maybe just some light oil in the wheel bearings instead of grease, since I believe they'll have external seals over them anyway.
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Sep 12, 2015 02:58
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So we regeared it for NJ, up 1 tooth in the front. Turned out not to be enough. On a clear lap, I was able to go WOT in top gear for the entire lap. But the rear brake was fixed and it ran reliably enough that I could compete for not-last place. The guy I was fighting with had a honda Z50 engine, a horizontal 4 stroke of some kind. I was able to hit the turns harder than him, he was braking in some places whereas I never touched the brakes, but I wasn't doing good starts and his motor had me on the main straight. He used all the track, too, so combined with my lack of skill, it was tough to get by him. And you can't do any aggressive late-braking maneuvers when you're never touching the brake anyway. In one of the races, I wasn't able to get past him until like the last lap. And so I wasn't able to build up enough of a lead on the remaining turns to hold position on the straight. But on the other race, I got past him about halfway through the race, so I was able to build up a lead and hold it until the end. So that was p. rad. I'm cheap, so here are some ripoff photos from the serious photographer who was at the track: Behind the 670/14 group, all 3 of us were real close most of the race. 14 Isn't in my class, though. Here's me behind them in turns 2-3 I think.  And here's me having passed them a while earlier and just barely staying ahead at the end of the straight going into turn 1.  So I went home with a 2nd and a 3rd. I gotta hand it to Yamaha, I ran that thing in 2 races and 2 practices, WOT under full load for almost the entire time, and it never skipped a beat. So now it's winter rebuild time. Gotta decide what to spend money on. I'd like some alloy rims and sprockets and clipons and a different tach. Probably we'll have to keep it down to the stuff we don't have to buy. So gonna pull the motor apart, widen all the ports a little, see about loving with the head to increase compression ratio, and try hydroforming an exhaust.
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Sep 27, 2015 03:16
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I'd bet he doesn't have any motor on you, just gearing. Looking for more power without having a good reason (or knowing where you want that power) is sorta putting a very expensive cart in front of the horse, IMO. Front sprockets should be cheap, if you just use different fronts you should be able to get within spitting distance of something resembling reasonable gearing.
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Sep 27, 2015 09:15
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The gearing was only an issue at that one track which won't be seen until September next year. The guy I want to be competing with (because he has the same motor as me) up front has a nice fairing and some motor mods. Although not many motor mods. Also has a totally different frame and wheels, so I'm wondering who has the advantage there. I picked some relatively wide (2.75") 17" tires for this bike but most people in the old 50s have 18" narrower ones, some of them 2.0 even. So far I think I'm seeing why they don't take anything wider, which is I've never gotten it that far over, so a fairly wide margin of the edge of the tire isn't getting used. But maybe that's just because I'm not going fast enough and leaning it hard enough. Especially at NJ it's absolutely amazing how sensitive the steering is on that bike, I have to be incredibly light on the bars to keep it smooth. The steering angle we gave it doesn't look that crazy to me but maybe it's wrong, or maybe it needs a damper, or maybe bigger wheels, or maybe a longer wheelbase. On the other hand if I just touch it real real gentle like it does seem to work, so maybe I should just learn to work with it. Oh and here's my greatest trophy yet  And at this last event there were a lot of other things to see, a vintage car race club, and some guy with a bunch of 80s Ducati race bikes on display, but who cares about those, this is the thing I wanna see:   An actual original 80s (maybe?) Kreidler 50cc GP bike. It is just the weirdest looking thing in person. It's like a foot high and the bars are like 10" tip to tip and ridiculously long. The ergonomics on it look like the worst I've ever seen on a bike. But it has a trellis frame and it revs to 17,000. Wow.
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Sep 27, 2015 13:39
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Rev. Dr. Moses P. Lester posted:The gearing was only an issue at that one track which won't be seen until September next year. The guy I want to be competing with (because he has the same motor as me) up front has a nice fairing and some motor mods. Although not many motor mods. Also has a totally different frame and wheels, so I'm wondering who has the advantage there. I picked some relatively wide (2.75") 17" tires for this bike but most people in the old 50s have 18" narrower ones, some of them 2.0 even. So far I think I'm seeing why they don't take anything wider, which is I've never gotten it that far over, so a fairly wide margin of the edge of the tire isn't getting used. But maybe that's just because I'm not going fast enough and leaning it hard enough. That Kriedler is fantastic. You probably don't need wider wheels - scrubbing rotating weight by running narrow wheels is a time honored tradition of lightweight bike riders looking for more acceleration. The less rotating mass you have, the better off you are. If you're not sliding the bike at max lean, you don't need more tire yet. Also, if you're running wider tires but unable to get to the edges of them, you've probably got some tire profile issues (due to either pinched or stretched sidewall), although that may be not really fixable, depending on the availability of your tires/wheel sizes. Fairings are hugely helpful to aero - I saw about +8 mph on the Brammo thanks to fairing, so I highly recommend prioritizing a fairing, followed by figuring out if you can get a performance oriented tire, and fit that tire to exactly the wheel size, with a preference to smaller rim setups. Try and figure out your gearing so that you always have ~1.5k of good power left in top gear at the end of the longest straight on your track. If you've got a range within that space, then you can change the gearing for individual corner setup, but I have a feeling your best bet is to just optimize so you have some power headroom at the end of your longest straight for when you pick up a little more speed during the race. Really sensitive steering is pretty much a staple of lightweight race bikes - damper isn't going to fix the geometry issues (it'll just force slower inputs, which you can do by hand). Tune your bike for midcorner feel, not straightline stuff. If it feels good in the corners, doesn't deflect uncomfortably over bumps, etc, then just focus on riding technique and staying off the bars over adjusting the geometry.
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Sep 27, 2015 18:46
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Ordered a gasket kit, clipons (they're amazingly cheap for 27mm forks), new tach. Pulled the motor today for the rebuild and mods. Noticed something. https://www.youtube.com/watch?v=LrtoBUjb6TE It had always been kinda rattly. I figured that's just how jap crap sounds, brah! Turns out it's got a crank bearing on the way out. I rode it around NJMP at WOT for about 45 minutes total, over redline half the time, like that. Pretty sure it was already like that because it always made that noise. Amazing.
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Nov 4, 2015 03:13
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If you think about it, those crank bearings are way, way over-built for how much power the engine actually makes which probably explains why nothing went wrong.
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Nov 4, 2015 07:05
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Rev. Dr. Moses P. Lester posted:Had a drag race today against a Buddy 50 scooter with a Prima pipe. (it's a p. fast scooter if you're not aware, bro) I won. So I'm feeling optimistic. If I was gonna build that pipe, I would do it this way:
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Nov 5, 2015 02:25
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Yeah that's the standard way motogp teams do it. But that's a psychotic amount of work. We might be able to just cut 2 things out of 20 gauge steel and weld the seams and pump it full of water.
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Nov 5, 2015 02:59
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Pulled the motor apart today. Amazingly there is no case gasket in this thing. The manufacturing is so good that they just used a little RTV and that's all it takes to keep the bottom end and gearbox perfectly sealed.  Magneto side of the crank didn't look that great, and I think I found the reason for that side's bearing being hosed.  The hosed bearing.  Little baby transmission.  Clutch big enough for a 125 motorcycle except that it only has 2 friction plates in it.  Top end with more fins than a motherfuck. Japs love keeping things cool.  One of many things I intend to lighten or remove. This is an idler gear that went between the clutch and the kicker and the speedo drive gear. Gonna remove the kicker entirely so I'm thinking about drilling a lot of holes in this heavy steel gear.  Piston looked amazingly good considering what I had recently been doing to it. 
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Nov 7, 2015 03:50
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Rev. Dr. Moses P. Lester posted:Pulled the motor apart today. I can't tell if you're joking or not but that's...pretty normal, I guess? Or do you mean it's unusual for an ancient two-stroke?
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Nov 7, 2015 05:01
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Yeah this thing is old and low tech enough to have an all iron cylinder. But I guess Japanese machining is Japanese machining.
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Nov 7, 2015 15:05
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My MB100 is from 1980 and has no case gasket. Got an iron sleeve in an alloy barrel though. Looks extremely similar to your engine structurally too, even down to the plastic oil pump gear.
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Nov 7, 2015 20:38
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Honestly those crank bearings are probably the same ones they used in a 125 or 250 bike or something, so yeah, to actually destroy the crank bearings would be a tall order for that motor. My rv90 uses similar size crank bearings as my Kawasaki 250. Same with the clutch, your hunch about it being from a bigger bike is probably true. Why design a new clutch when you can use parts you have and guarantee you'll never have clutch slipping problems?
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Nov 8, 2015 15:17
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Been doing random things but still a ways away from putting it all back together. Took apart the shocks, painted them something other than black.  In retrospect I wish I had painted the springs red.  Spent a lot of time wire brushing the paint off anything that was black.   And some things that weren't black.   Installed plugs in that cover to block off the seal holes where the kickstart shaft and oil pump shaft used to be. Got the motor all back together, well temporarily anyway. The top end is still undergoing some work.  Had some material welded into the head to up the compression ratio, shaped it into a sensible combustion chamber, then used some bondo to mold the inside of it and measure the squish band. Was like 3 times what it should be. So now the cylinder is at a machinist to be cut down a little to get the squish band right. Will have some pics of that before too long. For the previous few months I had intended to slightly modify the CDI to make the advance adjustable. I dunno if I mentioned that before. I used acetone to open up the original CDI and intended to replicate it with a potentiometer in place of one of the resistors in it. Here's what was in the original CDI.  Amazingly simple. Here's my interpretation of what that poo poo is. It was verified correct by a real life engineering student. So don't question it.  I even mocked up a copy of it with a potentiometer on a breadboard, ready to try out when the engine is back together. But having done all that, I've decided to abandon it. Instead I've decided to build a new ignition system from scratch in a totally different design using an Arduino to make a fully software mappable ignition curve. Two reasons I wanted to do this. One, the stock magneto rotor on this bike is loving massive and loving heavy and has to be a big source of parasitic drag on such a tiny engine. Here's what one looks like taken apart:  It weighs like a pound or two. My other reason is that the reading I've done in multiple 2t tuning books suggests that 2t engines benefit from having totally nonlinear advance curves. The RPM compared with the combustion flame propagation must be considered, like a 4 stroke, but also it must be considered that at different RPMs the fuel/air charge in the cylinder will be of varying quality due to the gas flow between the top and bottom end, the shape of the exhaust, etc., and will therefore burn at different rates. Sometimes the air/fuel will be diluted with exhaust gases which weren't evacuated totally from the last combustion etc. So I will set up a transistorized system with no magneto, running on a total loss battery, probably some small lithium thing. It will use a crank position sensor from a BMW K bike, because it uses a hall effect sensor for easy reading at the arduino and because it happens to be of a shape that lends itself to attachment to the side of the crank on this thing. More pics of this will come. Also, got all the supplies I need to hydroform the exhaust. Got some 20ga steel sheets and some weldable attachments for a pressure washer. Once the bike is all back together, I'll be trying and failing several times at that. I have enough sheet metal to make like 8 exhausts, I hope that's enough. Meanwhile, a fiberglass guy I know through the racing club is making me a custom fairing tank and seat. Here's a progress pic with the bare frame.  Oh and I got some of these cause I heard they're the poo poo. 
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Jan 16, 2016 04:25
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The custom ignition thing is cool as hell and you need to update on your progress with it. Stupid question, though and I think you covered it before but I'm an idiot and can't search to save my life - what's the redline on this thing? From what I remember from playing with my arduino it's pretty easy to confuse it when things are happening fast, but for all I know it could be more than capable of handling 14k RPM in a 2 stroke motor.
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Jan 16, 2016 15:47
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I was gonna say, is the arduino fast enough to keep up with a little engine spinning at a billion rpm?
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Jan 16, 2016 16:11
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I think it should be capable. A quick search of Arduino tachometers shows people recording more than 20krpm reliably. Should be gently caress-all code to make it happen, too. Please share any work on that Rev. I'd be interested in building something similar when I rebuild my Bantam.
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Jan 16, 2016 16:27
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