Sprocket Mod

I follow a couple forums about Honda Rebel motorcycles. There is a great deal of

information available there about repair and maintenance, and users share their

experiences about various modifications they have made to their bikes. One such

mod that has been discussed at length is replacing the fourteen tooth drive sprocket

with a fifteen tooth. There seem to be strong feelings on the subject either way, and

since the process is relatively inexpensive and completely reversible, I decided to try

it myself. Below are some photos I took during the surgery for the benefit of those

who may be entertaining the idea of giving it a try. Since it involves removing the

chain guard and loosening the rear wheel, I cleaned the chain at the same time.

Mine is an ‘09 CMX 250 built for the U.S. market. Details on other Rebels may vary.

I decided that it would be easiest to accomplish this with the rear wheel off the floor.

There are lifts available that are perfect for the job. They hook onto the sides of the

swing arm, and allow you to lift the back end quite easily. I don’t have one, so I used

a floor jack, with some

blocks of 2x4 and plywood

to support the weight of

the bike from the front of

the swing arm. It is not a

good idea to jack your

bike up by any part of the

exhaust system.

I find it preferable to

loosen the axle before

jacking the wheel up,

because it’s more stable

when torquing on the axle.

Use a shallow socket on

the end of the axle, and

another on the axle nut to

loosen it. Once the axle is

loose, jack the rear end

up. If you have one of

those nifty lift things, good

for you. If you use a jack,

lift the bike up by the front

of the swingarm, using the

blocks of wood to keep

the exhaust off the jack.

check carefully to make

sure you don’t catch the

chain, smash any hoses

or wires, etc. The rear of

the bike should be just

high enough to get the tire off the

ground, and stable enough not to fall

if you push on it some. I use a block

of 2x4 under the side stand to

stabilize it. There is a threaded stud

sticking out of the end of the swing

arm on either side. It has an

adjustment nut, and another nut to

lock the adjustment nut in place.

Loosen the outer nut on each first.

Use caution not to use too much

force on these nuts, as the

adjustment stud will break easily if

you over torque, or forget to loosen

the locking nut before wrenching on

the adjustment nut. Loosen the

adjusters on both sides to allow the

wheel to slide all the way forward.

Next, remove the chain guard. There

are three screws. Two are in plain

sight; the third is hidden behind the

chain. After that, remove the gear

shift lever. The shift lever clamps onto

the end of the shaft by means of a

bolt. The head of the bolt is to the

rear of the top end. Remove the bolt, and pull the shift lever off by pulling straight out

with your fingers. It shouldn’t take much force. Behind that is the rear crankcase

cover. It’s held in place by two screws. The lower screw also holds a clip that keeps

some wires in place. Remove the two screws and the clip. The cover should slide

straight out toward you. Behind it you will see the front sprocket, and probably a

deposit of crud that has been thrown

off the chain. Depending on whether

you use oil or wax on your chain, the

crud will either be oily or waxy. On the

face of the sprocket, you will see an

oval retainer, held in place by two

small bolts. I found it easiest to

remove them with the transmission in

gear, but there are several ways to

immobilize the sprocket. The torques

involved are not major. With the bolts

out, the oval retainer should rotate on

the shaft so that it will line up with the

splines and slide off. There should be

enough slack in the chain to allow

you to pull the sprocket out with the

chain around it. It should slide out

with some wiggling. This is the point

at which I cleaned both the chain,

and the area around the shaft. I used

kerosene and a Grunge Brush. If you

don’t have a Grunge Brush, get one.

They are available online, and at

some retailers. Drop the chain off the

rear sprocket, and let it hang down

into a container of kerosene. You

should have enough slack to soak

and scrub about a foot of chain at a

time. While a section is soaking,

scrub the area around the shaft, as

well as the inside of the cover with

the brush and a rag damp with

kerosene. I was careful not to let

kerosene come in contact with the

bearings around the shaft. I don’t

know for a fact that it will hurt

anything, but thinning the oil there

probably is not good.

The next step is to put the new

sprocket in place. I doesn’t look like it

will fit with the chain around it, but it

will. I put it on without the chain first,

just to get a feel for how it will line up

and slide in place. Put the chain

around the new sprocket, line it up on

the shaft, and rotate it slightly to get it

lined up with the splines. It will

probably take some wiggling to get it

to go on, but it will.

Please note that the side of the sprocket with markings on it faces in. The side facing

out has no stampings. The rest is pretty straightforward reassembly. Put everything

back in place, torque to specs, adjust the chain tension, lube the chain, and align the

rear wheel.

I haven’t put many miles on my bike since the transplant, so I can’t say anything

definitive about the results. The ratios have changed so that each gear has a slightly

higher range. This doesn’t appreciably increase top end speed, but it does mean that

my RPMs are lower at a given speed, and so far I’m happy with it. I’ll update in a few

hundred miles when I know more.