Rear Sprocket Modification
Rear Sprocket Modification
  After the stock saddle, the next most popular complaint about the ACE is that it always seems to be looking for a 6th gear. You don't notice this too much in the city but on those long highway trips, the higher revs of the Honda engine makes for a lot more noise and an uncomfortable high-pitched vibration when you are trying to cruise along at highway speeds. I can't count how many times I have hit the shifter while accelerating onto the Queensway, only to find that I am already in 5th gear.

  There is a solution for this though. You can change out your rear drive sprocket to a smaller one, decreasing the gear-ratio and causing the engine to rev less at the same highway speeds. Of course, you don't get something for nothing in the real world and the trade off here is that you lose some torque at the lower end.

  What size sprocket you pick will depend on what you are willing to sacrifice and how your bike is set-up. The original rear sprocket on the ACE is 41 teeth and the most common size replacement sprockets are 37, 38 and 39 teeth.

  The 37 is the most radical change in ratio. You can really cruise along with a lot lower RPM's then the original set-up, but you also lose the most torque at the low end. From all that I have seen and read, I would suggest you only go to a 37 if you have done some mod's on your ACE to increase horsepower; such as aftermarket exhaust, re-jetting the carbs and/or using a modified air kit. The extra HP will make up for the loss of torque. Otherwise, you would probably find that the stock ACE would have a hard time off the line, with frequent stalls and increased clutch wear.

  At the other end is the 39 tooth sprocket. This sprocket will make the least difference in power and should be easy for any rider to get used to, while still making enough difference at highway speeds to make it worthwhile.

  I chose the 38 tooth sprocket. After doing the research, it seemed that this sprocket was the most common one picked by Ace riders. And while I haven't done anything too radical to my engine power, I have punched the baffles in my exhaust and that should help compensate for any power loss I get on the low end. I also plan on installing stiffer clutch springs to help prevent slippage caused by having to rev a bit higher off the line.

  This project is pretty inexpensive and fairly straightforward to do. The only really expensive requirement is having some sort of bike lift since you have to take the rear tire off and need to get the bike pretty high up in the air to do that. I paid $159 for a Canadian Tire bike lift, but I am sure I will get my moneys worth back by using it a lot in the future. The sprocket itself was only about $60 Canadian after exchange and shipping.

Materials & Tools Needed
  1. Replacement Sprocket. Mine was a 38 Tooth Steel Sprocket, PN 815-38S from Sprocket Specialists. Also available from Billski Mods. I recommend you use only a steel sprocket as aluminum wears a lot faster;
  2. A new chain, if your old one has a lot of miles on it and is stretched. By going to a smaller sprocket, you really have to move the wheel back to make the original chain fit. Or you can shorten your old chain (which I won't go into here). I re-used my old chain as it had very little stretch, but when it was all back together, the adjustment was almost maxed out, so by next season, I might need to buy a new chain;
  3. Wrenches and Sockets. I used a big-ass 27mm wrench for the axle nut.; 3/8" and 1/4" sockets, sizes 8 mm, 10 mm, 12 mm, 14 mm, 19 mm and 20 mm;
  4. Bike Lift. You need something to lift your bike high enough to drop the rear tire out and back under the fender;
  5. A soft-faced hammer to help with the axle;
  6. Basic cleaning and lubrication supplies. To clean up the wheel and axle and lubrication for your chain, etc
Step 1:

While the bike is still on the ground, loosen the 5 nuts (1) holding the old sprocket on and also loosen the rear axle nut (2). I also removed my chrome chain cover at this time to give me easier access.
Step 2:

Lift the bike and secure it. Remove the rear brake adjustment nut (3) and pull the brake lever off the rod. Take out the barrel pin (4) so as not to lose it.
Click to Enlarge
Step 3:

Remove the brake stopper arm (5) from the brake cover by removing the cotter pin (6) and nut (7) and then removing the bolt, washer and rubber grommet.

Loosen the chain tension by turning the adjustment screws (8) clockwise all the way. Then remove the chain off the sprocket. Take the axle nut (9) and washer off and either have someone support the tire, or block it up with some scrap wood. Then remove the axle from the left hand side. Two spacers will drop out as you do this, one on the right-hand side of the wheel and the other on the left. Just remember that the larger spacer goes on the left and the thin spacer goes on the right. Lower the tire straight down and then remove it out the rear, under the fender.
Step 4:

Finish removing the rear sprocket. Now's a good time to clean up those spokes and the hub in that area behind the sprocket that was always so hard to get at when it's on the bike.

Here's a picture of the old and new sprockets (click to enlarge). Notice how the new one is smaller and how it's also cut out to save weight.
Click to Enlarge
Step 5:

Install the new sprocket. The side that is recessed faces out. Snug up the nuts holding the sprocket. Save the final torque until the wheel is back on and the bike is on the ground.

Here's a pic of the new sprocket installed on my tire.
Click to Enlarge
Click to Enlarge Now is also a good time to take the rear brake out and give it a good cleaning and inspection. I knocked all the loose brake dust off the brake assy. and then cleaned the drum and wheel.
Click to Enlarge Then I did a close inspection of the drum surface. My brakes looked great after only 12,000 km's.
One thing I did find was some corrosion on the aluminum axle. I believe this was caused by the steel spacers. With the spacers being steel and the axle aluminum, you can get dissimilar metal corrosion. I had a bit of difficulty getting the axle out because of this. So before putting the wheel back on, I cleaned up the axle with some WD40 and some scotch-brite Click to Enlarge
Step 6:

Now you have to put the wheel back on. It helps a lot if someone else can hold the wheel in place, while you slide the axle in.

Note: Make sure to put the chain over the sprocket before putting the axle through. It's a bummer to get it all together and then see that the chain isn't on, lol.

With the wheel being held in place, slide the axle through from the left side. As you move it in, position the first spacer in place, then continue through the wheel. Then, as it comes out the other side of the wheel, put the other spacer on and finally slide the axle the rest of the way through. Put the washer on and thread the axle nut hand tight.

Rotate the brake cover and re-install the stopper arm. Make sure you use a new cotter pin. Then put the barrel pin back in the brake lever, insert the brake rod back through and thread the adjustment nut back on. Don't thread it all the way on yet.

Snug up the axle nut just a bit, and then adjust your chain tension by turning the adjustment screws counter-clockwise. Move each side in small amounts to avoid binding the axle and when you have the proper tension, make sure the wheel is square by aligning the index marks on both adjusters. To see the drive chain tensioning procedure in full, click HERE.

Now adjust your rear brake with the adjustment nut. You want to have about 20-30mm of free play at the pedal before the brakes apply. Make sure the half circle cut-out in the brake adjustment nut fits over the barrel pin when you're done.

I also took this opportunity to clean and lubricate the chain while the bike was on the lift and the chain easily accessible.

When everything is ok, tighten the axle nut up as much as you can on the lift. Then lower the bike to the ground and torque the nut to 69 lb.ft. Move the bike back and forward a few times and check that the chain tension is ok. Torque the five sprocket nuts to 65 lb.ft. in a criss-cross pattern and finally, re-install the chain guard, if you had removed it before.

Update: It looks like it's becoming harder and harder getting the steel sprockets direct from SS. However, I have heard they are still available at Billski Mods. So make sure to check them out as well.


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