Jackshaft Jackshaft ideas and Sprocket ratio help

Discussion in 'Transmission / Drivetrain' started by RocketPenguin, Jul 16, 2015.

  1. RocketPenguin

    RocketPenguin New Member

    Now, i have already asked both of these questions before, and never got any real answers/gave incorrect information.

    Lets start with the jackshaft.

    I am working on converting a bicycle into a chainsaw powered moped. For this, i will have the chainsaw mounted somewhere between the seat and the pedals, probably in the triangular opening. I will then have the clutch of the chainsaw lathed so that i am able to fit a #35 chain onto the already existing teeth (The clutch has 6 teeth). I will remove the pedals This is where i need suggestions/reassurance) and place two bearings into the pedal housing. I will then get a jackshaft of some sort (I was thinking, would a really big bolt work?) and mount two sprockets on it. I would then have the original bicycle chain go to the jackshaft (Onto the smallest sized sprocket possible, 17t. I am thinking of using 5/8 or 3/4 diameter jackshaft). The chain from the chainsaw engine would then also go to its own sprocket on the jackshaft.
    To simplify:
    6t sprocket on clutch (Drive) goes to
    X sprocket on Jackshaft (Driven)
    17t sprocket on Jackshaft (Drive) would then go to
    28t sprocket on 24-26" bicycle tire.

    The chain between the engine and jackshaft would be #35, and from jackshaft to bicycle would go back to #25.

    How many teeth would be needed on sprocket X in order to get the ratio down to 25:1?

    And for the jackshaft, i was thinking this:

    In the pedal housing, which can fit a bearing with an OD of 1.3-1.4" i would have two bearings, one on each end. They would either be pressure fitted, or i could have a a tension bolt or two holding them in. I would then find a bolt with either a 3/4 or 5/8 OD and around 6-10" long, and use that as the jackshaft. Possibly key it myself if needed, or lathe the OD down a little if needed (Would this weaken it? Reason i would like to use a bolt is because it is A, Cheaper, B, solves the problem of how do i prevent it from sliding out (Both sprockets will be on the same side), and C, one is already threaded, so i can simply put a nut on the other end to lock it from sliding out.) Both sprockets would be mounted onto the bolt/jackshaft via a key, or by tension screws. Probably keys. Or both.

    So, to simplify:
    Two bearings placed into pedal housing
    Bolt placed into bearings
    Both sprockets placed onto bolt, possibly with some spacers/nut before, locking the bolt and bearings into place
    Sprockets would be anchored to the bolt via key/tension screws
    a final nut would be placed onto the bolt to hold everything on and together.

    Would this method work?
    Any good place to purchase bearings that can handle ~5-10K rpm?
    What sized sprocket would i need?
    If any more information is needed, or further explanation, let me know. I can even attempt to draw a diagram.

    PS: Didn't know where to squeeze this in, but is probably important, the engine runs at about 10-14K rpm, with around 2-4HP, and is 42cc

  2. RocketPenguin

    RocketPenguin New Member

  3. HeadSmess

    HeadSmess Well-Known Member

    interesting...a chainsaw that runs #35 type chain rather than the standard 3/8 pitch "inverted link" they all use...

    good lucking machining the hardened steel.

    unfortunately i think you will find its better to make/source/modify a new bell with a mount to take a proper #35 sprocket. that is easily replaced if required.

    why LOWER the pitch in the secondary redux? smaller chain is weaker, and chain load rating reduces as the speed reduces. ie, the slower running chain should be the heavier one...

    also, for this reason, its best to get the most reduction in at the final chain also... a 17 to 28 in #25 to the wheel?

    have you actually held a 17t #25 in your hand? or the chain?



    bit over an inch across. a 28t will be smaller than your rear hub... at least find a chain drive electric scooter in the junkyard and steal its sprockets...

    25:1 is absolutely ridiculous unless you have 32" wheels perhaps?

    14-18:1 is about right...

    and 6 teeth is also rather harsh on the chain...try for ten at least.

    the engine, if you tached it as a chainsaw, will probably saw best at 7-8k... thats where it makes its maximum power, unless ported to do otherwise. the label and manual may say 14k is its maximum speed...but thats unloaded. most saws work best at 7-8 grand...

    figure your ratios for 14 grand and you will regret it.

    make a tuned pipe for 9 grand and then try it out though ;)

    any bearing is good for 10k rpm... get to 35k and re-ask the question :)

    sorry to be so negative... you bumped me :annoyed:
  4. RocketPenguin

    RocketPenguin New Member

    The original unmodified clutch does run an inverted chain. However, I thought that if I were to have a portion of the teeth lathed down (instead of the tooth running the entire length of the clutch, it would be narrow enough to carry a #35 chain. I can draw a diagram if needed.) And that's how I would get a chain to fit. No centering, no welding.

    Can only hope a brake lathe is good enough.

    Would be very expensive to have a custom designed bell produced. Nothing exists that I know of that fits a chainsaw crankshaft axle other than the bells/clutches designed for them.

    The reason being of reduction of pitch is because I don't want to go around changing the cassette of the bicycle. I would like to use the sprockets already on the bike to save money and time.

    Again, reason it works out like that is because the largest sprocket on the rear hub is 28t. So, in order to get the most optimal reduction is to use the smallest possible sprocket on the jackshaft. That, and if it was any bigger, the sprocket for the jackshagft to engine would have to be a 70t+. Again, money.

    Yea, I have held both. And yes, a bigger chain would be nice. But again, money and time.

    28t is the biggest sprocket on my rear hub. Would love to go to a bike boneyard, but because of my location, the nearest one is 5 hours away.

    I was originally aiming for that... But in another thread, I was talked out of it. I do have a few steep hills. However, I may just aim for 18:1 instead. How does one calculate that when there are three numbers? Ex: 47 : 15 : 3 . Random numbers, but how would I get it down to two?

    6 teeth on the chainsaw clutch, so no changing that.

    OK, that's good to know. It was more of an estimate/what other forum users were saying elsewhere about chainsaws. That, and as guide to tuning the carb said something about 14k being the max, but yes, this was without load. Will definitely take this into accommodation and aim for a lower number.

    XD would love a tuned pipe, but I don't have the skills, money, or time to do so. This is more of a fool around joke/project, not a full time commitment of money...

    This whole thing isn't a perminant thing or anything. I don't want to spend more than 100$ more on it (already have bike and chainsaw, so I imagine I can fit it in under 100$) its more of a proof of concept/practical joke/look I did something type of project. It is serious to an extent, the extent of being able to ride this for a little bit, but not a "this will take me to work/school for a few years" type of serious.

    You weren't negative, it was constructive criticism .

    Thanks for the few tips/replying to my thread!

    Oh, and any ideas on how I would fit a real sprocket onto the clutch, in a safe, stable, centered manner?
  5. HeadSmess

    HeadSmess Well-Known Member

    think of it like this...

    12:1 could be 3:1x4:1...

    or 3:1x2:1x2:1....

    16 to 1 could be 4:1x4:1, or 8:1x2:1....

    and, for the sprockets...

    start at the rear...

    28/17 x X/6=

    lets say you use 55 as X...


    for speed, get funky with pi, and the circumference of your wheel and how many times it rotates in a km...or mile....

    bike chain is 1/2 pitch, not #25. it may work. use HD chain in that final drive.

    and #35 is 3/8 pitch but i seriously doubt it will work but i dont mind being proven wrong :) chainsaws run skip-teeth and that tooth is shaped nothing like the roller in a chain...

    try setting up an angle grinder in this brake lathe rather than a cutting tool...

    if you have a brake lathe it should be able to do drum brakes and therefore be able to make a clutch bell from a lump of steel bar and a bearing...? its just some boring and stuff... at which point it would simply be a spigot on the bell and the sprocket mounts with a set screw or some bolts through it into the bell...

    yeah, they have no chuck...hmmm... no.a brake lathe is useless.
  6. RocketPenguin

    RocketPenguin New Member

    Ah, OK, I think I get it.

    The calculator from this forum calculates speed for me based off of the rpm, so I have a rough idea of what it is.

    Ahhh... Now looking into it again, I see this is true. Don't know where I got #25... So a bike chain is #50? That doesn't seem right...

    What do you mean by skip teeth? And yes, I know a standard roller chain won't fit in it, that's why I would use a lathe. All as fails, I can mount an angle grinder and go at it as carefully as possible.I have a few bells to spare.

    My friend (the drum operator) claims he can do it, and so I leave it at that. I don't know how good of an idea it would be to lathe an entire bell... It wouldn't be hardened/treated for the temp/friction....

    Thanks for the reply!
  7. HeadSmess

    HeadSmess Well-Known Member

    ok, you can use brake lathe to make a new clutch bell, if required...find your bearing, drill the blank out rough, REAM it for the bearing, then mount on arbor in the lathe. easy.

    youll find that most clutch bells are just a stamped piece of steel. nothing super serious. maybe high tensile but theres nothing stopping you from getting an inch or two offcut of bar from a machine shop...try it...they might be curious enough to make it for you for ....beer? just make it a bit heavier... an option ;) of course, if theres any cracks in the steel... its scrap.

    they should only get hot if theyre slipping which means they arent spinning fast enough, are being overloaded, or the springs are too hard.

    skip teeth...the link or tooth is actually on every second link... and its about equivalent to something twice the pitch.... 6/8 or 630 series... huge. clunky stuff they dont even use on big bikes anymore... a hayabusa now uses a smaller chain than what a 750 used in the 80's...

    that 6/8 (3/4?) and the 630 should be the hint ;)

    1/2"(4/8") is 4xx. 410, 415, 420, etc...
    5/8" is 5xx series...

    x10 is skinny...
    x25 is fat.
  8. RocketPenguin

    RocketPenguin New Member

    If I were to mount a real sprocket onto the clutch, what chain size should I go with, and what would the minimum possible teeth be? The bore can be from 1" to 3/4 inch.

    EDIT: Oh wow, I really got my chain sizes off. My bicycles chain is #40, not #25... No idea what I was thinking when I measured it.
    Last edited: Jul 19, 2015
  9. RocketPenguin

    RocketPenguin New Member

    OK, so I was thinking, lathe down the teeth of the chainsaw clutch so that the diameter becomes 3/4". Then, put a ~10t sprocket (Unknown chain size. This was calculated with #40 chain everywhere) on the clutch, and weld it in place, or use tension screws. A chain would go to a 60t sprocket on the jackshaft. Then, from the jackshaft, a 10t #40 sprocket would go to the 28t #40 sprocket on the rear tire. This gives a 16.8:1 ratio. Sound good? The only thing I am worried about is the clutch to jackshaft chain pitch/size. Whats the recommendation for high speed chain of such given requirements? I'm thinking standard #40 bike chain isn't strong enough for it... Or would it be more important on the jackshaft to tire? Which at that point, would no longer matter if the chain size of clutch to jackshaft would matter, right?