Help keeping the chain on my sprocket

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MisterSteve124

Guest
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
 

srdavo

Well-Known Member
Joined
Nov 4, 2006
Messages
3,162
yes ...let's see some pics. chain alignment has got to be really straight.
 
5

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.

Myron
 
M

MisterSteve124

Guest
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:

http://img517.imageshack.us/img517/4958/picture004jy7.jpg
http://img517.imageshack.us/img517/939/picture007hz8.jpg
http://img517.imageshack.us/img517/8610/picture009ts4.jpg
http://img517.imageshack.us/img517/7659/picture015tw2.jpg
http://img517.imageshack.us/img517/1160/picture016uy7.jpg
http://img517.imageshack.us/img517/5214/picture017cf8.jpg

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!
 
H

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

Alex
 
5

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.:eek:

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!:eek:

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.:eek:

Myron
 
M

MisterSteve124

Guest
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.
 
A

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.
 
5

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.
 
M

MisterSteve124

Guest
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.
 
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