Gearing for a Lifan monkey bike

[Deadbike]

Hello all.
I have a Lifan engined (old 3 speed) monkey bike. It seems very undergeared. On a steep hill nearby it tops out in 1st and 2nd gear and accelerates in 3rd before the hill runs out. Currently has a 15-33 rear drive, running a 15.5 inch diameter rear tyre. I have a new 17 tooth front and a 37 rear set of gears but this only changes the ratio from 2.2 to 2.1765. However if l make a 33 tooth rear sprocket my ratio becomes 1.94. My question is do you think this would be enough for my engine or could l reduce the final sprocket even more?

 

[Deadbike]

Should have added l am upping my chain and gears to a 428 set. That's why l have to make the new rear sprocket.

 

[Old Guy Too Many Bikes]

First, there's no need to up to a 428 chain, it will add friction and drag and actually slow you down a bit. Sprockets are cheap, trial and error sometimes is necessary to find a combination to match your riding style. On level ground, in high gear, topped out, do you feel there's power to spare. Try it on a slight upgrade, has your top speed decreased, if it does, a different sprocket won't help top speed. Often a one tooth increase on your countershaft won't increase top speed, but will decrease vibration and make for more relaxed cruising.

 

[Deadbike]

Thank you for the reply.
Couldn't find a larger sprocket for the front in the original chain size, but l found some cheap 428 chain and the sprockets were plentiful. I've even found a 34 tooth rear which doesn't need much work to fit. The engine revs out before 60kmh at the moment. My speedo is accurate at 30 mph / 47kph which I've tested on a warning signal locally which is accurate. So l decided to go down the sprocket route. I'll try the 34 rear and report back. I've just put a couole of pictures up of the bike. 🙂

 

[power6994]

Cool bike. Yeah you'll just have to play with it to see what you like. There are lots of variables like your size, do you live in an area with lots of hills? You'll get a feel for it

 

[Deadbike]

Yes l now live in Hastings which is mostly hills, and l weigh about 165lbs. I used to have an ST70 which l put a 90cc engine in which was called Desert Storm in a tea cup. Powder coated in a sand colour which was faster than this one. Got stolen and burned by some bastards!

 

[Old Guy Too Many Bikes]

I'm a little confused. you said it's a Monkey, but it's definitely a CT70. You said it's a 3 speed, but that motor looks like at least a 125 based on the size of the intake manifold, and ought to be a 4 speed. Also, I believe an 18 tooth 420 sprocket will fit, and are pretty easy to find on ebay. I was even able to find a 32 tooth rear sprocket for mine.

 

[Deadbike]

In England they were originally listed as an ST70 although mine had a DAX HONDA (shown below) sticker hidden under a pile of stickers that covered the bike. They were generally known as monkey bikes although l have seen some externally tube framed monkey bikes for sale more recently. The engine is an early Lican 125 with a neutral at the bottom and 3 gears up. I haven't seen an 18 tooth front sprocket, or a 32 tooth rear on e-bay yet but will continue my search.
Thank you.

 

[Old Guy Too Many Bikes]

I've never heard of a Lifan 125 with a 3 speed. Are you certain there isn't another gear hidden below your neutral? It's possible you may have a shift drum hanging up not allowing you to access all 4 gears.

 

[Deadbike]

It may be possible that there is a fourth gear that it won't select. When l've got it running again (the throttle cable broke the plastic bit in the handle). I'll run it with an 18 tooth front and 34 tooth rear sprocket that has now arrived from e-bay for a week to two then I'll tear down the gearbox and have a look. I suspect that it's fourth that's not selecting as it's way undergeared.

 

[Old Guy Too Many Bikes]

You should be able to access the shifting mechanism and shift drum without splitting the case. Since your motor has a manual clutch, it's more likely that you're missing first gear. Unlike Zongshen motors which are 4 up, Lifan motors are 1 down, 3 up. If you were missing 4th gear, you would have a neutral between 1st and 2nd. 18 / 34 is a good combination for a CT70 with a 125.

 

[Deadbike]

Well l've given it a run around with the 18-33 and it max's out at just about 50. Are you sure about 1st being missing? Because on page 12 here leel says that some early Likan engines had a n1234 shift pattern.

 

[Old Guy Too Many Bikes]

It's possible, but I've never seen a Lifan with a manual clutch that was 1 down and 3 up. Once you get a look at the shift drum and ratchet, you'll know for sure. If top speed is your goal, you might do a little better with a 17/33, but for cruising as 40-45 mph, 18/33 is a better choice.

 

[MiniBike Mike’s Garage]

It's possible, but I've never seen a Lifan with a manual clutch that was 1 down and 3 up. Once you get a look at the shift drum and ratchet, you'll know for sure. If top speed is your goal, you might do a little better with a 17/33, but for cruising as 40-45 mph, 18/33 is a better choice.

I can’t speak for Lifan engines built in the past couple years……but pre-Covid you could get a manual Lifan in both 1dn 3up or 4up. I have used a few of each. I preferred the 4up, due to it being almost impossible to find neutral on the 1dn 3up version, with the engine running.

 

[Deadbike]

Ok, well here l am. The bike runs with the 428 sprockets and chain, total cost £26.49 🙂. When l was out on it the other day l saw over 50, but forgot my speedo registers kilometers! I'll have a look at the gearbox and sort out the missing 4th gear. I'm also waiting on a delivery of a set of pilot and main jets, so will let you know how l get on.