Need help with gears on chainsaw bike

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
This is my first time building a chainsaw bike and im having trouble figuring out the best way to hook up the chain from my 42cc poulan pro to my aggressor gt 7 speed with 14t-34 t with the least amount of frame modifications possible and the best gear ratio. Any advice???
 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
I want to use my gears i figure it will b the most efficient im still at the beginning stage and don't want to screw up a $$1000 bike and don't want to waste my time on a **** one either but I get confused when it comes to the gear ratios
20210725_170515.jpg
20210725_170739.jpg
 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
Its a tight fit and no room for any kind of shock absorbers on the motor but I think I have that on down now I need to figure out the best way to mount the drive chain and still utilize my gears
 

Sidewinder Jerry

Well-Known Member
Dec 19, 2011
1,459
301
83
59
Rockwood, TN
If you paid a $1000 for that bike. Somebody stole a high dollar wheel off the back and replaced it with a 7 speed 34-14 freewheel (34,24,22,20,18,16,14). The higher end bikes use 8 speed and up cassettes instead of freewheels. It kinda of looks like a Kent frame and a blue spray paint job.

On my bike I use a custom built 7 speed freewheel (34,28,24,21,18,15,13). I also have a Staton Inc triple chainring shift kit. The chainrings are 28,36,44. I use a 4 stroke Robin Subaru 35 engine [33cc 1.6 hp]. The engine is ran through a Staton Inc 18.75:1 reduction gearbox. The RGB uses a 15:44 drive. The reduction range is 66.79:1 to 16.25:1.

It gets shifted like this:

Steep hill climbing and heavy load pulling
1(1-3)

Around town general use
2(3-5)

Open road use
3(5-7)

The only time chainrings will be shifted is when either using cogs (3) or (5). All shifting is done with the left hand. I also use a techometer to shift by.

I'm a large person and live in the mountains. The bike I built didn't come cheap.

Now you could get a Sick Bike Parts shift kit and I can even teach you how to build a 4 speed 34-16 freewheel or you could also use a 3 or 5 speed internal geared hub.
 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
Wow thats awesome man but I'm not really looking to go all out on this i just need to no wat the best way to mount the chain for reliability and simplicity i don't really have the capability to make parts or even understand pretty much anything u just saìd im just getting into this .. And lol the bike is a 2019 aggressor gt
 

Sidewinder Jerry

Well-Known Member
Dec 19, 2011
1,459
301
83
59
Rockwood, TN
So are you wanting to do a left side single ratio drive?

As for how to shift a 3x7 drive system on a bicycle it's done like this:
1(1-4), 2(2-5), 3(4-7) for 12 non redundant sequential gear ratios. Starting gears are 1(1) for stops going uphill. All other stops use 2(2).

A 3x8 is shifted like this:
1(1-5), 2(3-6), 3(5-8) for 13 non redundant sequential gear ratios. Starting gears are 1(1) for stops going uphill and 2(3) for all other stops.

If a gear is to easy or to hard to comfortably maintain a cadence (crank rpm) of 70-90 it means you're in the wrong gear. For pedal only purposes I always advise getting a bicycle computer with a cadence meter on it.

Never cross chain (big big or little little)
Never use both shifters at the same time
Never stand while shifting
Never shift while pedaling backwards
 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
No I was thinking about sticking to the right and maybe trying something like a jack shaft i want to still be able to use my peddles and gears. And thanx no one has ever explained how it works to me I just switch to whatever gear feels easiest at the time
 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
Ya now that i took closer look at it thats exactly wat im aiming for exept i am mounting the engine in the middle hope its guna work out like i kinda have planned... maybe
 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
So what would my optimal gear ratio be to keep top speed and still have climbing ability what gear would I put on the motor And the rear 7
 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
And without changing The ones I have in the back what would I use on the motor rate now I have 14 16 18 20 22 24 and 34T
 

Sidewinder Jerry

Well-Known Member
Dec 19, 2011
1,459
301
83
59
Rockwood, TN
Ok first you need a reduction for the engine. Chances are it turns more than 8000 rpms. So the rear wheel can't turn that fast. You'd also need a shift kit. I use a Staton Inc triple chainring shift kit.

Here's a video of Fabian building a triple chainring shift kit using a Sick Bike Parts shift kit.

 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
Kewl man , so until i get one built how can i hook it up right now that would gimi top speed
 

Sidewinder Jerry

Well-Known Member
Dec 19, 2011
1,459
301
83
59
Rockwood, TN
You can't run through your gears without a shift kit or the pedals will spin every time you use your engine. Much too dangerous. You can run a left side jack shaft. Then to the left side of the rear wheel. You'll need a better centrifugal clutch. Use a 9t sprocket on the clutch and run to a 36t sprocket on the jack shaft. Then put a 9t sprocket on the jack shaft and run it to a 36t sprocket on the left side of the rear wheel. This'll give you a 16:1 reduction.
 

Mrgoodcat

New Member
Jul 25, 2021
21
4
3
Ok thanx and do u know what that would give me for top speed? I'm aiming high, looking for something around 70km/h with maybe 5-6000rpm range on the motor is this possible? I'm getting conflicting information about this i want to Use a jackshaft to the gears on my rear tire with these specs 6t-44t motor to jack input and 32t-14t output to rear tire and it gives me a ratio of 3.208 with a top speed of 44.643mph BUT.... then I get this ..... y would it be so far off with the same gears??????
 

Attachments