Help with my Chainsaw bike

[MisterSteve124]

Ok so I am almost done with my chainsaw bike thanks to Locksmith for welding my sprocket on for me! But now I can't get the chain to stay on the bike gear. I have the chainsaw mounted over the rear tire and the chain runs from that down to the gears on the bike. But whenever I start the chainsaw it will usually stay on for like 30 seconds or so then it jumps off the sprocket. I have tried tightening the chain like as much as I can and it still keeps jumping off without me even giving it any gas, it's just idling. Any ideas? Thanks and I'll post pics once I'm done.

[bob-a-lu]

make the sprocket teeth bigger or dremel it out between the teeth.
Very Happy


oh and get pics PLEASE!

[homedepotpro]

are you sure everything is lined up straight. also it might do better with some resistance. are you just picking up the back wheel and letting it spin freely.

[hi]

yea, it sounds like its crooked.

[MisterSteve124]

yeah homedepotpro I am just letting it spin freely. Maybe I should just try and take it for a quick ride. But how straight do I need it to be? I mean I try to line it up straight as I can see. And I also tried lining it inwards towards the tire (to the left if you're looking at it from the back) so that it wouldn't go down to the other gears. Here are some pics:

[homedepotpro]

dude your gear ratio has got to be a little high (not that is has anything to do with the chain falling off, at least i think) And are running off the stock clutch, cuz with that ratio your really going to burn that thing up. You might want to think of reconnecting the pedals for getting your speed up enough.

[MisterSteve124]

Yeah I know the ratio isn't great but shouldn't it still work? What is an optimal gear ratio? Maybe I should try and change it.

[miskaman]

Your chain looks like it has a little bit too much slack in the 2nd picture. Try repositioning the engine.

[MisterSteve124]

Repositioning it where? And the chain is absolutely as tight as I could get it.

[homedepotpro]

i think is is some where aroung 8:1, but you also have to take into consideration the huge diameter of your drive wheel. right ratio or not, your clutch probably won't last very long, they're not really intended for this kind of stuff (this much torque).

[battlemonkey]

On a minimoto the ratio is 6-60 in terms of front and back sproket. they rev to about 10,000rpm. i don't know what that chainsaw will rev to but i don't think it will have the touque for that set up

[shud_b_rite]

Which end does the chain first come off? Maybe you could add another obstacle for the chain to go through. By that I mean you could place another free rotating sprocket close to the chainsaw sprocket or the bike sprocket. I know this probably isn't easy but i think it may help.

By the way that looks cool so far, you've done a good job on it.

[jrrdw]

Your chain is to tight, to straight up and down, (yes, that really does matter). Add the chain tensioner that came with the bike back into the mix at a fixed position but the gears free floating as they were before you took them off. Ask yourself this -- How is it that the chain stays on other bikes with the sagested 1/2" slack at the longest free floating stretch?

[Orpackrat]

A thought: a sprocket mounted on a shock or spring in the middle of the chain going down to provide tension.

[couchquail]

is that a 7 speed, 8/9 speed or bmx chain?
there is a difference. if it is bmx your rear cassette cogs are not space far enough apart to accommodate it.
as for your chain tension, i run my singlespeed chain with 1/4" deflection. if it is too tight i tend to stretch the chain and it fails prematurely. it never comes off it just breaks.