Posts tagged clutch:



i bought this doppler clutch pulley and rebuilt it per the instructions in the wiki. the fact that i have to rebuild a $220 pulley before it is even run is ridiculous, but i’m glad i did:

the quality control on this thing is dreadful. 

can’t really tell from the photo, but there are burrs, flashing, and the offset hole was cut out crooked.

my favorite part. hint: look at the springs–

look a little closer–

one of the springs wasn’t even on all the way from the factory. 

i had to grease ungreased bearings, file & sand surfaces so they would fit, and locktite every nut on it. nice try, doppler. should’ve waited for a mykitech. 

The consequences of power

I haven’t posted much about Black Butte in a while, but it’s been going well. Devin of Motion Left Mopeds recently provided me with 4 prototype pipes to compare with the St-Ripper, which has proven a little too rev-crazy for my build. I haven’t tested it again with the HPI and lightened weights, so maybe I should soon. I’ll avoid posting a photo of them in order to not reveal too many of Devin’s new designs, but they are all pretty different and give me a lot of options.

A reminder of current setup (the important things at least):

  • Athena with about 172 degrees of exhaust duration and opened up transfers (not widened)
  • Stock reed block with boyesen dual-stage mod reeds (more on these later)
  • Stock intake ground out to about 20mm (this will soon be replaced with a new intake with material added, ground out to 21mm+ and a smoother entry into the reed block
  • Puch magnum exhaust header to radiator hose intake hose deal
  • 21mm PHBG with velocity stack
  • Malossi MHR Delta clutch springs, the blue middle strength set (still ridiculously strong)
  • Derbi 6 roller variator with 15g of weight
  • 1977 house brand BX5 belt
  • HPI ignition, set to 2mm BTDC
  • Terry Dean Cain edition lightened and re-angled clutch bell, matches the angle of the derbi driven face
  • Starter clutch pulled, rope-start thingy attached to HPI rotor

I have been running the prototype pipe with the largest chamber, and it’s a real winner. Lots of torque all over the place, and it revs out nicely to the low 60s. I can get to 50 in about 10 seconds and just cruising around and then throttling on around 30mph is a blast. It’s a real winner and I think it could be finalized and sold as is as a competitor to the MMM Destroyer. Note that I haven’t run the Destroyer in a long time so I am not directly comparing them at the moment. I put about 60 miles on the bike during the Toledo rally and the bike performed perfectly, besides being somewhat tricky to start with the rope starter. The crank spins up incredibly quickly due to the HPI, which is great, as it makes the clutch grab much more firmly and with less slip, which puts power to the wheels more reliably and quickly. It also allows me to cruise around 30 with no big effort, as the clutch can stick at that speed. The torque is great, because I can throttle on to pass slower bikes or just have fun blasting down an open road, or slow down to take a corner and then throttle on through it.

Ryan cooked this rope start up for me. The pull-start setup simply won’t work with the HPI rotor, and I know Julian had been using a similar disc on his bike with good results, so I gave it a try. It does add 5oz of weight to the rotor, but it’s still laughably light compared to the nearly 2lb stock flywheel. I’m still figuring out how to reliably start it; it’s usually a combination of a hard pull and a quick blip of the throttle.

So since coming back from Toledo, I’ve wanted to test out the other 3 prototype pipes, and went down to the shop to do so. One of them seemed similar but not as fast as the pipe I was running, but that isn’t conclusive, as at the end of the night I noticed the freewheel on the rear wheel was rubbing against the pipe and ground a nice big groove into the inside. Slowing me down? Maybe. I pulled the pipe and installed another one, which looked to be designed for higher RPMs. Initial tests seemed interesting, but when riding back to the shop I noticed a strange sound, and when I stopped the bike stalled out and wouldn’t start back up. After checking for blown seals and any obvious leaks, I pulled the frame off the subframe, pulled the carb, and found this:

My bike ate my reed. :( This bike has maybe… 300 miles on it? I guess I blasted too hard… but I can’t be replacing these dual-stagers every few hundred miles, so I’ve ordered the .4mm carbon reeds and will see how those perform. I ran carbons once before on my yellow bike (which is a drastically different setup) and they just didn’t seem right AT ALL, but I’m hoping that they will be a good match for this setup.

Since I had pulled the clutch to check the seal, anyway, I decided to give it a quick sanding to get some fresh pad material against the clutch bell. Check out what strong springs do to a stock clutch:

What you are seeing here is that the arms of the clutch are bending and only the dark parts of the clutch pads are engaging the bell. This isn’t terrible, but I’m interested to see how long this clutch lasts. I should probably get a backup clutch on deck, and remove the black MHR springs from that other clutch I have to avoid premature stress. The real key is to sand down the pads and clean off the inside of the bell every 50-100 miles to avoid slipping. It’s a pain, but it’s the price you pay for running a setup like this. You can honestly do it in under 5 minutes if you are fast, though.

So probably no more pipe tests until this weekend. I’m sending Christian two of the MLM protos for testing on his new build (which I hope he posts about soon), but keeping the torquey pipe and a higher RPM pipe for my own use for now.

Oh, I also opened up my variator to check the weights. After 250-300 miles (estimated) they were beginning to flat spot a bit, but nothing terrible. I ordered 5g Dr. Pulley sliders and tossed 3 of them in there. I also compared the TJT ramp plate to the stock Derbi 6 roller plate. The difference was fairly obvious: the TJT ramp plate features an aggressive flat angled ramp surface that begins in the middle of the plate and continues to the edge. The Derbi plate is a smooth curved surface to the edge. The edges are exactly the same at the end, but I’m not sure if the flat surface would cause the variator to more fully open or not, resulting in a higher final “gear”. It appears to me that the Dr. Pulley sliders would match very well with the shape of the ramps on the TJT ramp plate, while only a small portion of the sliders would be pressing against the Derbi ramp plate. I put the Derbi plate back on, but am going to be testing the TJT plate as soon as the bike is back together and I am able to do some good testing, instead of changing like 4 things at once.

More to come later, of course.


Spring calls for springs. lol.

So the Black Butte has been in build stasis since mid-March. It performed admirably in Nashville, besides pretty drastic temperature issues. On the long, hilly, Saturday ride I was having to back off the throttle constantly due to hitting 425F far too often. This was causing serious heat fade as well, which I can tell you is very real and very annoying. My timing was as retarded as I could make it without completely eliminating low-end performance, and my jetting was definitely on the rich end. So my plans are some piston mods and continuing to lust after an ignition with an actual, you know, TIMING CURVE.

Another major issue was the low end, which wasn’t to the point of wretchedness, but certainly sucked for a Hobbit with pretty strong clutch springs. It almost felt like the clutch was slipping like a Puch, which definitely was disheartening, and made me worried about the porting Devin did for me out at MLM. An advanced timing would certainly help out, but would cause even worse heat issues up top, so I didn’t want to mess with it.

I decided to address this issue by getting the absolute strongest clutch springs I could find. A reasonable and well-thought-out approach, yeah? I also purchased a beefy set of circlip/snap ring pliers with a bunch of swappable arms. These give you the ability to stretch out the spring using leverage. The Hobbit clutch doesn’t have a really nice variety of leverage points to work from, but with the right tips you can JUST get the springs to catch on the edge of the hole and then smash it in with some taps from a hammer. I first put the medium springs in one spare clutch, and after I figured out the technique I got the three strongest springs in by myself in 10 minutes or so.

So the initial tests were definitely BETTER, but it was still slipping and not really launching me the way I wanted. I got to thinking and realized maybe the inside of my clutch bell had a bunch of glazed pad material on it, so I pulled it, sanded the inside surface down, sanded the clutch pads, and put it all back together. Holy crap, what a difference. The clutch grabbed hard at some stupid RPM and the front wheel came up a little even with a bunch of my considerable bulk pressing down on the bars. It’s borderline unsafe. I didn’t test much besides a few parking lot revs, due to increasing darkness and my fear of ending up on the side of the dark road due to an unforseen 45mph wheelie.

I think I can now try to use the St-Ripper again, as I might be able to launch right into the pipe, or close to it at least. If it wasn’t raining, and I wasn’t leaving for the weekend, I would do that IMMEDIATELY. Devin also has a few new pipes for me to test and will be giving them to me at the Thunderdrome races at the end of this month.

So current status: hitting 61.5 or so with my 195lb self on it. My much lighter friend Ryan gave it a spin last evening and hit a ridiculous 64.5. I need to lose some weight.

Next steps: weak-ends rear pulley mod and stiff spring installation, pipe experiments, wheelies.


Mo parts mo problems, swapping points ignition

So I got some stuff recently:

Derbi 6-roller variator and a cool clutch bell I’ll get into more later.

Another clutch, shown here with the Malossi springs already installed. Leo Vince springs in the package.

Set of Polini tuning weights. This is the “light” set, but I had ordered the “superlight”. Figured more weights couldn’t hurt, and the 2 lightest overlapped the 2 heaviest in the superlight set. They aren’t meant to be run for the long-term, but offer a cost-effective way of finding the weight you need for your rollers.

So back to that Derbi variator and clutch bell. Last season Terry Dean Cain made a really cool build, a dual-dual variated setup called Black Betty. Unfortunately, it was too much bike for too little racing and he decided to save some of it and sell other parts off. I asked if he was also selling the lightened and lathed clutch bell and Derbi variator from the build, and thankfully he was. Derbi 6 rollers are a pain in the butt to find, and the clutch bell was lightened and the angle was matched to the cheek of the Derbi variator. Custom performance parts for a good price? Some more clutches and clutch springs? Another PA-2 complete variator? Don’t mind if I do, TDC.

So I was really hopeful that these parts would make a big difference over the TJT variator I was trying to tune with. But first I wanted to swap out the points ignition from my 1980 PA-2 for the CDI that came on the 83. Why? Well there has been some discussion on Moped Army about whether or not the stock CDI is rev-limited, or just really sucks at high RPMs, or what. I have been having a really hard time revving out fully, and it felt like there was actual hesitation up top. I knew that some other pro Hobbit tuners had run 60+ with points, so I figured it was easy enough to test out. So I got down to business.

So take your beefy-as-all-hell strap wrench (you DO have a strap wrench right? It’s the #1 tool I use in the shop these days) and wrap up that flywheel. Torque off the nut and slide it off. This reveals the flywheel mount plate with the stator beneath it:

You have to use a 2-arm puller to get that thing off. Trust me, there is no other way. So get that thing in position:

and torque the end nut down. The flywheel mount will literally explode off. Make sure you keep the woodruff key in sight, it’s tiny. For full disclosure: I actually ended up using a different puller we had in the shop, the arms on this one were too big and couldn’t fit between the coils right. Remove the stator mounting bolts, and pull it out, taking the wire bundle along with it. Be sure to disconnect all the wires from the rest of the bike before you do this. Duh.

This stuff makes your bike go vroom. I also removed the HT coils because they are a little different from one another. NO PHOTOS THOUGH!! I repeated this process on the CDI-based ‘83, a bit faster this time because the puller fit around the coils a lot more easily. Thread the wires back through the hole  on the cases and connect them up. Because I had simplified the wiring really hardcore on the ‘83, it was extremely simple to swap to points. I just had to make a little jumper to connect the coil to the kill switch. Putting the CDI on the ‘80 might be harder, but it’s no biggie.

To put the flywheel back on, put the woodruff key in the slot on the crank, and slide the flywheel mount on. The 3 holes will fit into the flywheel in only one way, so get it on there and get it seated.

Then use your trusty strap wrench to hold it and torque that flywheel nut down tight. DONE. And it started right up first try, amazing.

So I then tried to see if the CDI had been holding me back. Sadly, that didn’t seem to be the case. Whatever, at least I knew that the CDI probably wasn’t the issue but didn’t have to worry about it anymore. I then started testing things. I quickly wanted to test the new clutch springs and such, so after a few runs I pulled off my old clutch to find this:

GOOD WORK DIO SPRING. You sucked anyway. Nowhere near strong enough for this setup. The new Malossi springs are designed for a different bike and have a nice, fairly moderate engagement zone. Not ridiculous but better than these. Combined with the removed starter clutch the low end was feeling really good.

Unfortunately, things aren’t working out elsewhere. No matter how I change the weights, I’m hitting high 50’s. I spent over 2 hours just going a mile up and down the road, coming back and changing weights. The bike either will rev out pretty well, but not fully variate, or won’t rev out as far and variate farther. The results are still all between 55-58, even with the MLM St-Ripper. Maybe I’m just not making enough engine power?? I just don’t know. I’m going to test more later, using even lighter weights to see what happens. I’m getting concerned that my carburation is the issue, so I’m going to take a good look at my reed plate and intake, open up the reed plate openings and grind out the intake some more. I know people who go 60+ on a 19mm phbg and a stock reed plate, so I have to be doing something wrong…

So yeah, I’m pretty disappointed right now. I still have 2+ weeks of tuning before Nashville, though! I know I can do it, eventually… right?

Oh yeah, I also had this amazing issue where the brass ring inside the Derbi variator decided to grind itself down on the clutch bell mounting rod, resulting in brass dust getting everywhere and it now looking like it won’t mount flush. Hooray! Ruined my brand new (to me) Derbi variator in a few hours!! I think those brass rings are just pressed in, so I will talk to Ryan about a fix. Maybe they are the same size as the stock Hobbit one?



So the Hobbit clutch is pretty good, yeah? Dry, seems to handle high speeds well without warping, tunable via replaceable springs, etc. The main issue is that the only springs that seem to work very easily (or at all) are SOME scooter springs, the most commonly employed of which are for the Dio. They come in 1k, 1.5k, and 2k RPM versions which are progressively stronger, for later clutch engagement and making your bike do wheelies and you fall on the ground. Major issue with this is that even the strongest ones aren’t that strong when you are talking about ultra blasty times, which is what my build is shooting for.

So I took apart my clutch last night to see if I could drill some weight off the arms. Less weight = less mass pulling at the springs = later clutch engagement, I hoped. Here’s what I ended up with:

So those 3 holes in the arm weren’t there before. This was a pain in the ass, even with a corded drill and what I believe were metal drilling bits. The arms weighed about 52.5g before modification and 50g after. Hardly worth it. I’m not sure I could safely drill out more weight on the meat of the arm - the majority of the weight seems to be in the clutch pad material, which is very dense.

I’m currently in the hunt for a variety of scooter springs for tests. Maybe some of the Malossi ones will work. Or Leo Vince.