Need help with figuring out sprocket sizes for my custom fl350

[Odysseyninja]

So I have an odyssey fl350 frame that I am putting an 07 ninja 500 motor in. I took the original gearbox out and i am using the final drive shaft and gear out of the gearbox. I will be making housings for double row ball bearings that fit the shaft and adapting a sprocket onto the gear. I want to gear it to go about 80mph but i am planning to run a jackshaft because i want to keep the final drive sprocket small, no bigger than the disc brake, or smaller. If someone can help me out on figuring out what size sprockets I would need or point me in the right direction to accomplish this gearing, that would be great!

[LiveWire]

You're not going to get 80. I would not gear higher than 75. You can get more HP modifying the 350 2 stroke than what a 500 Ninja makes stock.

All these numbers are pulled out of my a$$, fill in real ones.

If the bike would do 120 and you are gearing for 75, bike tire was say 25 and Odyssey tires are 20 (actual height, not what the sidewall says)

120/75 X 20/25 = 1.28

Bike has say 15 tooth front, 60 tooth rear sprocket would be 4:1 reduction. 4x1.28=5.12 ratio desired.

Figure out the sprocket count that would give you a final sprocket the size of the brake rotor. Let's say that is 64 and you use a 15 on the engine. 64/15=4.27

5.12/4.27=1.2 meaning you need a 1.2:1 ratio between the number of teeth on each end of the jack shaft. Bigger sprockets on the jackshaft will reduce chain heat on the first chain.


Did you already take the gear box apart? Was it working before hand? Are the U-joints in the axles tight?

[Odysseyninja]

[LiveWire]

A pipe, intake and carb change would get you similar power out of the FL350 engine.

The axles are no longer available so if you break one later, you are out of luck. I would start with more off the shelf parts to begin with like axles for a 4x4 Honda quad. You already have to fab up the center spool. It would not be much more to change the wheel bearing carriers to a new setup.

[Carlriddle]

Yeah, if the FRN was ok I'd sell it to fund the redo of rear end.  It looks like you have near 0 chain length.  But the easier would be prob sell the 500 ninja and pickup a sled w/cvt and drop it in and run the honda box.

[LiveWire]

Porting the 350 engine, pipe, intake and carb and a water cooled head would be even easier yet.

A twin sled engine either needs to be mounted up high or the frame cut on the right to clear the recoil.

I personally would sooner adapt a CR500 cylinder on the 350 cases than swap in a different engine. I have a 53cc big bore engine I built that I have to get around to installing. I want to build one with a CR500 cylinder next. Nicom plated at 91mm, it will be 101cc oversize.

[Odysseyninja]

Sounds like nobody likes the idea of a ninja 500, I like it because I will now have gears to add to the fun and I got the motor practically for free. I won't have to spend money on fixing the 350 motor either, and I like the challenge. Anyways I think I figuered out my sprocket sizes, I found a sprocket/ gear ratio calculator that I used. http://www.bikerenews.com/Stories_Archives/GearRpmSpeedCalculator.htm

If I have a 16t on the engine, then a 40t to a 16t on the jack shaft, then another 40t on the drive shaft I should be at the ratio I want. The 40t sprockets are about 8 1/2" in diameter so I think this will work. If the 350 motor has similar power as the ninja motor than the axles should have no problem handling it. Thanks for the input everyone, I will post more when I have more progress.

[LiveWire]

No one likes it because they have either gone down a similar road or heard the horror stories from those who have. The idea of wanting gears is only appealing until you actually have to use them. Others on this board with bike engines have big engines with big torque that can hold a gear for a while. Some of those would still prefer a CVT if it were not that bike engines are cheaper than sled engines. You may not be spending money on the 350 engine, but you will be spending money on the conversion. I have owned an FL350R for 17 years. I have seen many people talk about putting bike engines in. I have seen many failed projects sold. I have never seen one at a riding trip or race with someone actually riding and enjoying the machine. The thing I find the greatest about an FL350R is you can ride for a season then enhance it, ride more, enhance more. You actually get to use it during it's evolution from stock to full on modified. An engine swap is not ride able for a long time if it ever actually does get done and working.

The second chain will see 2.5 times the load of the first with the sprockets you listed. The second chain will snap. You could run double or triple chains from the jackshaft to the final drive.

The U-joints don't break from torque, they break from being a pivot in the suspension. You are already modifying the inner connection point of the axle. At that point, you might as well replace the single weakest design point of the entire machine. If you don't want to figure out a different setup, swap out the axles to ones using heavy duty off the shelf joints like a 1350 that would otherwise not clear the FNR case.