Trouble Shooting

QuickThinker · Jan 5, 2014

I NEED IMPUT

I Went about mounting an engine ordered a centrifugal clutch and had everything perfect started the engine and the clutch engages at a higher rpm than the engine can accomplish although the engine was rated for 3000 the clutch engages at 2200 so I decided to over haul my mount went to a friction drive and lo and behold engine under performed could not get over ten mph, my engine is a lifan 2.5 97.7 cc ordered from home depot and I need to know how to not sacrafice torqe for speed yet achieve just that, would like chain drive back im willing to put a couple hundred into the pot to go 30 and climb some nasty hills around my town

maniac57 · Jan 5, 2014

Guessing from your post you have a lifan four stroke and you want it geared for decent power.
Most four strokes need a jackshaft for extra reduction. Did you buy a kit with a trans? How is your final drive setup? What size rollers have you tried on the friction setup? Remember the china two stroke has a reduction primary.
We need more info to really help you.

QuickThinker · Jan 5, 2014

No I figured that there weren't any kits for a bmx bike setup so I had only thought that the engine I had was okay by itself I am Not experienced with engines or gear ratios and things I am a carpenter on the other hand so framing around the end of the bike came easy I did have the clutch An 11tooth and the drive gear a 73 tooth that mounted around the hub and to the spokes when I configured the frame to friction I used a sleeve of metal that mounted around the shaft and made the diameter around 2 inches

maniac57 · Jan 5, 2014

Try a smaller roller. I have seen several friction drive setups with a 1 3/4 roller...don't give up before you experiment a bit.
As far as chain drive, you would need a huge rear gear with that 11 tooth front cog.
Think something in the 80-110 tooth range with no reduction between the engine and wheel.

Moto pope · Jan 5, 2014

I run that same engine with an AGC jack shaft and clutch set for 79cc power curve. manic mech. hub adapter and rear sproket. Bike does top of around 25mph, but also does pretty well on our hillie streets.

QuickThinker · Jan 5, 2014

Okay. So if I went the gear reduction route how would I go about it? I couldnt say im sure but a jack shaft or a torqe converter?

QuickThinker · Jan 5, 2014

So on another note my clutch is the max torqe ss? Ive looked everywhere for replacement springs to lower engagement rpm but im not even sure what the engine can achieve you said you have the same engine? Should I just invest in another clutch :/

maniac57 · Jan 5, 2014

Read the four stroke section of the forum for lots of good info. You don't even know what questions to ask yet.
READ! Seriously, most questions are answered there.

MotorBicycleRacing · Jan 5, 2014

QuickThinker said:
No I figured that there weren't any kits for a bmx bike setup so I had only thought that the engine I had was okay by itself I am Not experienced with engines or gear ratios and things I am a carpenter on the other hand so framing around the end of the bike came easy I did have the clutch An 11tooth and the drive gear a 73 tooth that mounted around the hub and to the spokes when I configured the frame to friction I used a sleeve of metal that mounted around the shaft and made the diameter around 2 inches

What overall diameter are the tires on your BMX?

Also 2" is a high speed friction roller.
Friction drive rollers are usually in the 1 1/8" to 1 1/2" diameter range although your motor is low revving which will limit your speed.

Using the gear ratio calculator you input the roller diameter where the bike wheel size normally goes.

Friction drive rollers give the same ratio on any wheel size.

Mike B · Jan 5, 2014

You need to figure out the gearing needed to get 20-25 mph at ~ 4000 engine rpm.

Forget 30.

Start with the tire diameter and work back.

Forget speed, torque is more important. If you gear too low you just don't go as fast. If you gear too high you don't go at all. Especially if you have hills. That poor clutch will be slipping like mad and the motor will be straining, the clutch will be smoking and you will be going nowhere.

QuickThinker · Jan 5, 2014

So i looked it up if i have my ratio 1:5 it would work?

QuickThinker · Jan 5, 2014

Do I need somthing fancy? im so mentally exausted from trying to figure it out

Mike B · Jan 5, 2014

You need about 10 to 12.

scotto- · Jan 6, 2014

Mike B said:
You need about 10 to 12.

Better yet about 12 to 15:1 final gear reduction for that engine being chain driven.

Moto pope · Jan 6, 2014

QT, If you have not removed the governor from the motor, this is the only way to get the necessary rpm you need. I am not advertising for any merchant, but again, the AGC web site has a how-to area with step by step instructions on how to do this. Their 79cc clutch has a high launch rpm to make up for lack of power, and allows a higher gear ratio for some top end gain. Also, while you are inside the motor, disable the "low oil" switch which can shut motor down while in a turn, where oil goes to one side of motor" as stated, read...

MotorBicycleRacing · Jan 6, 2014

QuickThinker said:
So on another note my clutch is the max torqe ss? Ive looked everywhere for replacement springs to lower engagement rpm but im not even sure what the engine can achieve you said you have the same engine? Should I just invest in another clutch :/

Affordable Go Karts has springs for the Max Torque clutch.

What size wheels does your BMX have because that will change your gearing ratio.

rogergendron1 · Jan 6, 2014

a 97cc lifan should be almost capable of wheelies ! you hav geared wrong and i would not go friction drive with that motor ! try an i frame mount and gear acordingly

MotorBicycleRacing · Jan 6, 2014

rogergendron1 said:
a 97cc lifan should be almost capable of wheelies ! you hav geared wrong and i would not go friction drive with that motor ! try an i frame mount and gear acordingly

His Lifan is a low revving 5/8" shaft utility motor bought from HOME DEPOT if you read the post.

Lifan makes all kinds of motors and It ain't a motorcycle type motor like you are "thinking"?

His motor will not pull wheelies.

rogergendron1 · Jan 6, 2014

if your rear monting it you should make a nice sturdy mount plate and go with chain drive .

you need to go with a 10 or 11 t drive sprocket on a centrifugal clutch and run it to a j shaft .... the j shaft could be as simple as 2 pillow blocks on the mounting plate close to the motor with a 5/8 shaft about 6 in long. on one side you have a stop bushing and on the motor side you have 2 sprockets.... one sprocket is the driven sprocket, you run the chain from the 10t cent clutch to the j shaft driven sprocket then right next to that asprocket you put on a drive sprocket and run a chain from that to a rear tire sprocket. using a mani mechanic adapter will make life easy .

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