Motorcycle Velocity Stacks

by Maxlarsen Apr 3, 2017
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Hi, Max,
nice work!
if you don't mind a dumb newbie question...how many hours is in the design of something like this?
They look very similar to the rams for a Weber DCOE side-draft carburetor. The rams available aren't great design, with a flared lip. Good rams should have a full radius lip like yours.
Weber ones are machined to slot into the carburettor body about 40mm, not sit on top like all the designs I have found.

Hi Andy,

Thank you so much for your comment. In answer to your question, it took about four days of work to finish these. I believe that these are something like the fourth or fifth version of my design for these. The most difficult part was perfecting the fit of the stacks into the engine. It was very hard to take measurements on the velocity stacks, because of their weird shape. I was basing these off of the original velocity stacks that came with the motorcycle, but without any kind of numbers or models to work off of, it ate into my time to keep testing the fit of different prints. Back to your question though, after I finished modeling them which didn't take too long (I would say that the majority of the modeling that I had to do took about 4 hours, between the measuring, and the calculations on the velocity stacks that I had to work with, and then translating that into a functional model).Printing them out is really what took up the most time. My printer was almost constantly running for three days, printing out different versions of the velocity stacks to ensure they would fit properly in the engine, and figure out what I needed to do to adjust them, if they were still off, because the really annoying thing is that they would fit, but would be too loose, or the screw holes would be off, and with something like this, it obviously has to be exact, and so I ended up having to play a little bit of a guessing game to find the exact measurements that would allow my 3D printed velocity stacks to fit into the engine well.

Let me know if you have any more questions,

Good stuff. What material did you use to print them and how has well has it done with the heat?

I used ABS to print these. There isn't too much heat in that part of the engine, and even after we ran it in the motorcycle on the highway for about half an hour, it was fine. It wasn't much hotter than when we started. The stock parts are actually made out of ABS as well.

Do you think PLA Will be ok too?

I don’t think it would be a good idea to print these out of PLA. There is a lot of vibration in the engine, and PLA is a brittle material brittle, that I worry it would actually fracture in the engine. What you need is a material that is a bit more ductile, and something that will last. ABS is the better solution because of its ductility, and the fact that exposure to the moisture in the air doesn’t affect ABS. In short, I wouldn’t use PLA. I just don’t think it would work properly.

Ok, thank you! i never print Abs yet, have printer about 2 weeks , i like it, ive Heard it's too difficult, any specs for print it you can recommend please? thank you!

For this specific model, I would recommend using rafts as the base of the model is very small, and it will help keep the support in line during the print to have rafts. I print ABS at 225 C, with a heated bed at a temperature of 100 C. I print at a speed of 3200 mm/min. For this specific model, I would use a medium to high infill, and make sure that everything is properly supported. The best way to really dial in your settings for printing with ABS, is to print something small (One small test kind of part I made is here: https://www.thingiverse.com/thing:1729056 ), and start with some standard ABS settings found online, or try the ones I have provided here. From there, continue printing that small model, while varying different temperature and speed settings to see what combination gives you the best final print. It takes a little time to do this, but once you have found the settings you like, you should be able to print in ABS without any trouble. If you have any other questions, feel free to send me a message :)

Lego Brick

What printer are you using? btw ive heard Petg is a good material to do this too. what do you think? i see your stacks and looks really good, im building some stacks for CBR throttle bodies but these Will be adaptes in a car. Thank you for your replies, i really appreciate it a lot!

I'm using a Flashforge creator (the wooden one) for all my prints, and simplify3D as my slicer. To be honest, I don't know much about PETG. What you are really looking for in a material, is something that won't ever fracture in a brittle manner. You need something that deforms elastically, and plastically, when working in this part of the engine. You need something that can withstand a higher strain. That's why both the original manufacturer, and I used ABS for this part. From what I can see online, PETG seems to have ductile properties, allowing it to deform somewhat plastically, so it may work. If you can test both materials, or find someone online who has done a sort of stress-strain test on both of these materials, you should be able to determine whether or not PETG would be a suitable replacement. This would be the case if the strain the PETG can take is simliar in value to that of ABS. As long as those two values are close, PETG should work.

Ok, yesterday i printed one piece in ABS, not the good printing specs as rafts, hight temperatura to the bed (just 45 ºC) and 255ºC, left as it and today see a good piece! first piece i did was a dissaster so i tried a second piece as it, just for testing, and got this one, whie piece, the blue piece is made in PLA plastic. I tri to bend both pieces and the more resistence is PLA :S. ABS sound it Will crack, PLA is more resistence , "flexible"? from what i see so far , about mechanical capacity i'd go with PLA really, but when i start on this Project i was worried about temperatura resistance because it Will be fitted under a car Hood, after to see this abs piece printed i dont know, make me have even more doubts about it! i know ABS normally is used a lot..any input? thank you!

PS. ABS i got is new, never open, 1.75 ABS.

Well, I'm not sure what kind of temperatures you're going to be dealing with for your specific setup, but the amount of heat in the area of the engine you are working in is definitely something to consider. If you are on the edge about whether to use ABS or PLA, ABS has a glass transition temperature of about 105 C, and PLA has a glass transition temperature of about 60 C. You'll want to leave a factor of safety on this part that you're making, so you should probably never subject this part to anymore than about 1/2 the glass transition temperature. If this part of the engine won't go above 30 C, then PLA is probably a safe choice in terms of temperature. If you are expecting temperatures in this area of the engine greater than 30 C, but less than about 50 C, you'll want to go with ABS. The other thing to consider is that fact that PLA is a biodegradable thermoplastic so any kind of use as a part of a larger machine becomes impractical. PLA will degrade over time, (I'm not sure exactly how long), however ABS will not ever degrade which makes it a safer choice for this kind of a part. While the PLA is new (freshly printed), it may be more flexible, but over time, as it is in contact with air, it will degrade and become more brittle. This will not happen with ABS (It will not degrade, and will hold its flexibility) which is one of the reasons why it is the choice of most manufacturers, and the better material choice for these kinds of parts.