Sprockets Looking for a Semi Specific Sprocket?

Discussion in 'Transmission / Drivetrain' started by RocketPenguin, May 31, 2015.

  1. RocketPenguin

    RocketPenguin New Member

    Hello World!
    First time on this forum, just finished reading rules and guidelines. If i make any mistake, please notify me so i can correct it as soon as possible.

    Currently building myself a motorized bicycle using a 42cc chainsaw engine with 2-4HP and an old bike of mine. More or less have everything figured out, except one thing. I am now at the current stage of figuring out what sized sprocket to place on the clutch of the chainsaw. How i plan on doing it is quite simple. First, i get the sprocket, and using a lathe, i will bore out ~29.8mm-30mm hole from the center (The sprocket on the chainsaw clutch for the chainsaw chain is 30mm in diameter). I will also have two rings with the same inner diameter made, and will have both placed on the opposite sides of the sprocket. I will then use a hydraulic press to sandwich all of this onto the chainsaw sprocket. In order: Chainsaw clutch, spacer ring, sprocket, spacer ring. May possibly put a few weld beads between it all to secure it. This will all go back onto the chainsaw, and be mounted on my bike.
    Any objections? Any tips? Would this work? Did i post this in the right spot?

    Second question, mostly pertaining to the title and the sprocket.
    I haven't really worked much with sprockets, so i need a bit of help with this. I need a sprocket that: Has the smallest number of teeth, Has a current bore size of 30mm or smaller, and/or can have the center bored out to 30mm without structurally clasping/ the low end of the teeth getting in the way (Basically, the lowest point of the outer diameter must exceed ~35mm, or a number where if the bore is 30mm, the teeth don't like fall off or something. You know what i mean.).

    Chain? I am not 100% of what size i will be using, but lets just say, i don't want to change the sprocket on the bike, however, i don't think bike chain is strong enough to withstand the chainsaw. With that said, is it possible to have one sprocket match the chain size, and the other sprocket be a little bit smaller? I currently don't know what size of chain i am going to be using, so thickness is currently semi irrelevant. Would also like this answered.

    So where could i purchase such a sprocket, or at least, what should i be looking for? Number of teeth? All i could find were sprockets with too large bore sizes, or not enough teeth to have a 30mm bore size.

    EDIT: Bore size of sprocket can range anywhere from 18mm diameter to 30mm diameter.
    Last edited: May 31, 2015

  2. The_Aleman

    The_Aleman Active Member

    I know of this 17T aluminum #41 blank with a 1" diameter bore. Overall diameter will be roughly 2.7"

    link: http://www.jackssmallengines.com/Parts-Lookup/T520317/3316000/PL

    You would need to do some work on the teeth, less or more depending on 41, 415, or 410 chain. The sprocket has unfinished edges.

    Hope this helps. If not, let me know what kind of reduction system you're building and we can try to find a smaller sprocket.
  3. RocketPenguin

    RocketPenguin New Member

    Ok, I guess I could explain what I am doing.
    Basically, I will have the engine mounted above the pedals. I will then have a chain going from the chainsaw clutch sprocket (What I am looking for) to the biggest gear on the pedal axle. I will then have the original bike chain go from the smallest gear on the pedal shaft go to the largest gear on the back tire. Long story short, I am using the pedal axle as a jack shaft. Of course, the pedals will be removed.
    And keep this in mind: This largest thing about the project is this: Use the least amount of money possible.
    I don't want to re sprocket the entire bike. The point of this isn't to have a long term, functional bike. Heck, if the bears give out in a week, doesn't matter. I have everything, except the sprocket and extra chain. I had the chainsaw lying around. The bike was an old one of mine that I have since upgraded. I just finished tuning up and fixing the chainsaw for a whopping 10$. Preferably, I would like to keep the cost under 30-40$.
    However, that was one worry that kinda got me. Looking into it, 25 chain can't really handle (Maximum RPM of chainsaw)13000 RPM... Or even 8000 RPM. (Though I would love to see it try. However, I value my life, but then maybe I don't)
    As for finding a smaller sprocket, I can lathe the axle/bore of the chainsaw sprocket down to 18mm in diameter. For the chain, it cannot be wider than 8.5mm, in theory. In reality, it cannot be wider than 8mm. I could go for replacing the sprocket on the bike (As I may have to with a #40 chain) so long as it is cheap. One issue, however, is finding a sprocket that fits on my hub... Haven't actually looked at my bike's from cassette, hopefully its forgiving enough. Definitely don't want to replace the sprocket on the tire and the sprocket on the pedal axle going to the rear tire.