Help keeping the chain on my sprocket

Discussion in 'Rack Mounted Engines' started by MisterSteve124, Oct 28, 2007.

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  1. Ok so I am almost done my chainsaw bike and I have the chainsaw mounted over the rear tire. And the chainsaw clutch has a 13 tooth gear on it which just connects with the original sprockets on my mountain bike. The chain that I'm using is a little bit wider than the original bike chain but it still rolls fine on the sprockets. But when ever I start the chainsaw up and try to just spin the tire the chain jumps off the gear it's on. Can someone help me fix this or give me any advice I can post pictures if needed. Thanks

  2. srdavo

    srdavo Active Member

    yes ...let's see some pics. chain alignment has got to be really straight.
  3. 5-7HEAVEN

    5-7HEAVEN Guest

    :cool:Ditto on the chain alignment.

    which gear sprocket are you aligned with? there can be only one that you can be aligned with, unless you somehow re-arranged the derailleur.

    Furthermore, your gear ratio must be very high, like maybe 2:1 if you're geared to the 26t sprocket. that is, unless your chainsaw has a gear reduction box of 7.5:1 or numerically higher.

    FWIW, my gear ratio is 16.67:1.

  4. Well srdavo told me that my gear ratio is way off so got any ideas on how to set one up for what I have here's the pics:

    Sorry there's a lot I just wanted to make sure you guys could see everything so you can give me the best advice possible. Oh and right now its on a 13 tooth drive sprocket and its going to a 36 tooth sprcoket on the bike Thanks!
  5. Hardcarve1

    Hardcarve1 Guest

    From what I can see you have mounted the motor off an horizontal tube only. I would install vertical tubes down to the centre of the wheel to take the load that will be pulled by the chain. When the motor is driving the load will be between the motor drive sprocket and the sprocket on the wheel trying to pull themself together. Looks cool

  6. 5-7HEAVEN

    5-7HEAVEN Guest

    :cool:Steve, i remember you from previous posts. you were so impatient to install the engine so you could ride the bike this summer. you just wanted to assemble the bike, then work out the bugs.

    now here you are.:rolleyes:

    good news first, then the bad news. Steve, it looks like a very clean installation. using the bike's gear is a step in the right direction.

    bad news next. engine mount needs more support. it seems like the engine is floating upon that aftermarket rack. maybe two support legs to the rear dropout area would help, ala STATON friction drive supports.

    the REAL bad news is that your final gear ratio is WAY OFF. your 13t drive sprocket and 36t driven sprocket results in 2.76:1 gearing.

    let's compare your rpm output with a 8500rpm MITSUBISHI 2.2hp engine(mine). my final gear is 16.67:1. for the sake of comparison, i will calculate everything on a 26" bike.

    at 10mph, your engine rpm is 350rpm; mine is at 2100rpm.
    at 20mph, your engine rpm is 700rpm; mine is at 4200rpm.
    at 30mph, your engine rpm is 1050rpm;mine is at 6300rpm.
    at 40mph, your engine rpm is 1400rpm;mine is at 8200rpm.
    at 41.35mph,ur engine rpm is 1450rpm;mine is at max hp range at 8500rpm.
    at 243mph,your engine rpm is at max hp range at 8500rpm.:shock:

    your clutch will burn out before you reach 10mph.

    comparing my 16.67 gearing with a happy time engine, it'd be like 10t engine sprocket and 41t rear sprocket.

    with your 13t sprocket and 36t rear sprocket, it'd be like 10t engine sprocket and a SIX-TOOTH sprocket in the rear!:shock:

    Changing engine sprocket to 6-tooth still would not correct your error. shooting for 14.76:1 final gear(happy-time with 36t rear sprocket), you need to install a jackshaft to reduce gearing an ADDITIONAL 5.35:1, preferably one that links the 36t driven sprocket with a 7t jackshaft sprocket.

    either that, or keep your 13t engine sprocket and install a 192-tooth rear sprocket.:shock:

  7. Well I'll focus on the gear ratio first since that's a much bigger problem. My only problem is I can't think of any place to set up a jacksaft to give it a better gear ratio.
  8. Alaskavan

    Alaskavan Guest

    It looks like you have some room forward and under the engine. You can usually find go-kart jackshaft set ups on ebay pretty cheap. You may need to shift the engine over one way or the other to maintain alignment with the driven gear. Good pictures.
  9. 5-7HEAVEN

    5-7HEAVEN Guest

    :cool:BTW, the chain might be jumping off because the links are too wide. after you find the correct gearing, you can use a better-fitting chain.

    then again, the chain might be jumping off because the engine platform is flexing. two to four support arms might solve that problem.
  10. So if I find a go kart jackshaft set up think I can bolt it or get it welded on there somewhere?

    Update: I tried riding it today and it worked (sorta) I only went about 10mph just with the engine idling and not giving it any gas at all because when I started to give it gas it didn't seem to do anything but make the whole bike and chain vibrate more. And after about 10 minutes of riding the clutch started smoking. If I just took the springs out of the clutch would that just disable it? Because right now I don't think it's working because the clutch drum was really tight getting it on so it may not even be working since it might not even be rolling on the needle bearing.
    Last edited by a moderator: Oct 30, 2007
  11. japat100

    japat100 Guest

    better read again and take advice what 5-7HEAVEN has posted ,,

    why try keep your chain on ,this setup will only burn out your clutch ,, you were lucky when you gave it more throttle that it did not sick on ,,because if your motor ever got up to 8,000 rpm you would have been going 220 mph ,

    you got to gear down ,and when you do your clutch will be fine ,,these power saw clutches are very good and should last a long while ,, like i say read 5-7-heaven post again
    Last edited by a moderator: Oct 30, 2007
  12. I know but if you look at the pictures I can't think of how I could set up a jackshaft there's not much room, any ideas? I found a jackshaft that I might be able to get to work but what size gears should I use for the two?
  13. srdavo

    srdavo Active Member

  14. That sorta looks like what I am now thinking about doing, except I don't think I can use 2 jackshafts. How do I calculate the gear ratio with 4 gears. I found jackshafts with a 10 tooth sprocket and a 14 tooth sprocket and one with a 13 tooth sprocket and an 18 tooth sprocket. Maybe I could buy the 18 tooth one and buy a 10tooth sprocket and use that or vice versa with the 10 tooth and buy a bigger sprocket. But what would be good sizes? And should I be looking at a 3/4" shaft or 5/8" or does it not matter. I'm hoping that I can just get the bearing hangers welded on either side of the rack mount and then get two bars reinforcing the bike rack to the frame so it can't flex as much. Get what I'm saying or should I draw something up in paint? Thanks for all your help guys
  15. 5-7HEAVEN

    5-7HEAVEN Guest

    :cool:Now you're thinking, Steve!

    Let's compare your setup with a happy-time engine with 41-tooth rear sprocket. with its 10-tooth engine sprocket, that computes to 4.1:1. multiply that to the engine's built-in gear reduction of 4.1:1, and you get 16.81:1.

    that's your final drive goal...on or about 16.81:1.

    your 36t driven sprocket will link to a 8t on the right side of your new jackshaft.this results in 4.5:1 ratio. dividing 16.81 by 4.5 gets 3.74:1. on the left side of the same jackshaft, slide a 30t sprocket. change your engine sprocket to 8t, which then links to that 30t jackshaft. this ratio is 3.75:1.

    with 16.81:1 as your goal, you have 36t/8t(4.5:1) and 30t/8t(3.75:1). multiply 4.5 X 3.75 = EXTREMELY close match.

    your new combination of gear ratio will duplicate the mph/engine rpm comparison chart i posted earlier.

    Sooo, you'd have an 8t engine sprocket linked to a 30t jackshaft sprocket, left side. an 8t jackshaft sprocket is on the right side, which is aligned and chained to the cassette's 36t sprocket.

    if you're able to aquire these exact-sized sprockets(not 9t,10t,28t,29t sprockets), you would be able to gear down, using just one jackshaft.

    because the jackshaft will be short and chain tension relatively light, i think that 5/8" shaft is sufficient.

    always remember that the engine AND the jackshaft will need independent adjustability.

    now go look for those gears. You will not find this combination in a universal $30 kit. each piece must be individually selected, and are available at various websites. unsure about the 30t sprocket with 5/8" bore.

    and be sure to get the matching chains. you MIGHT have a problem finding a sprocket and chain to match the 36t cassette driven sprocket. if you can't find a thin-enough sprocket to fit the bicycle chain, i've heard that BMX chains might work. if not, ya might have to machine the teeth of the 8t sprocket narrower, to fit the bicycle chain.

    Last edited by a moderator: Oct 31, 2007
  16. The only problem is I can't change the engine sprocket. I got it welded onto the outer clutch housing. Is there any way I can still get a good gear ratio using the 13 tooth?
  17. 5-7HEAVEN

    5-7HEAVEN Guest

    :cool:That changes the combinations, and forces you to use TWO jackshafts.

    Okay, 13t engine sprocket/22t jackshaft sprocket, right side. left side sprocket, same shaft, is 8t. second jackshaft, left side is 18t; right-side sprocket on second shaft is 8t, and is aligned directly with 36t wheel sprocket.

    now, 22t/13t=1.69:1
    18t/8t= 2.21:1

    1.69 X 4.50 X 2.21 = 16.81, the EXACT final drive goal you were shooting for, and comparable to happy time/41t.

    for more low-end, change 18t to 20t.comparable to happy time/46t.

    for more top end, change that same 18t to 15t. comparable to happy time/35t.

    Last edited by a moderator: Oct 31, 2007
  18. japat100

    japat100 Guest

    one thing is to check to see what hp you are running ,,power saw could have more cc then happy time ,,so you may get away with a little less reduction and 1 jack shaft
  19. 5-7HEAVEN

    5-7HEAVEN Guest

    :cool:The most logical method is to find out at what rpm does maximum hp occur, and gear your bike's maximum speed accordingly.

    or for riders interested in low end torque, find out at what rpm does maximum torque occur, and stay in that rpm range.

  20. Can't I get close with just one. I don't have the money to just be buying 2 jackshafts. What if I just get like a 10 tooth sprocket and a like 30 tooth sprocket or something. How close can I get with just one jackshaft and my 13 tooth drive sprocket? Ok I get that I can't really just use 1 jackshaft unless I get like a 38 tooth sprocket to use or something that will probably be way too big. I can't find a 22 tooth sprocket though. There are 20's but I can't find a 22. What size should I get if I need to use with my bike chain. I'm almost positive it's not 35 I was thinking maybe 40 or 41. Anyone have any idea? and do you think it would be ok just to attach the jackshaft by getting the bearing supports welded directly to the bike rack?
    Last edited by a moderator: Oct 31, 2007