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Randy O's


Detailed procedure for changing to a 16 tooth drive sprocket to a 1991+ Nighthawk 750

PREFACE Following my long trip across various western states, I was curious if there was a way to lower the highway RPM's a bit on the 750 Nighthawk. I e-mailed a Honda dealer, and they recommended a 16 tooth counter-sprocket (the stock is a 15 tooth). Well, since my chain was nearing the end of its useful life, and I needed a new rear tire (11,270 miles), I figured it was time to be brave and attempt my first major mechanical task (although for one as mechanically challenged as myself, installing the luggage rack/ backrest could be classified as a major task).

With the exception of the actual mounting of the tire and balancing, I performed all of the tasks myself. If I can do it, anyone can. Below is a detailed, step by step list of what I did, including some observations and warnings. By the way, it was worth the effort. Previously, at 75 mph (indicated) on the highway, my Nighthawk was turning 5,000 rpm. It now turns about 4,600. On the ow side of fifth gear, I used to turn 3,000 rpm at 45 mph. Now it turns about 2600 rpm. The other advantage in my opinion is cornering. In the low speed turns (say 15-25 mph), it always felt like 2nd gear was too low a gear and 3rd a bit too high. Now, the gears seem more matched to my riding style. I'm sure the gas mileage will improve. I will post the info after a few tankfuls. I don't ride my bike like a "crotch-rocket", so what little low end punch was lost was not evident to me. It still has plenty of "punch" left.

MPG REPORT: 1st Tankful -- Looks like around a 5% increase in MPG. I didn't baby anything, and even did a bit of "spirited" riding. In the past I would have ended up around 38 to 39 with that type of riding. This time it was 41.7. For the next tank, I will back off to my normal riding style and commute, and see what happens.

2nd Tankful -- The increase remains. This was a more normal couple of days for me, just my commute to work, with a side trip to Oakland, about 80% highway, speed varied between 65 to 75. I only glot feisty and gunned it once! This type of riding would usually come in at 40 to 41 mpg, however, with the new 16 tooth sprocket--43.3 mpg.

Last Update -- It doesn't seem to matter what type of riding you do, you should experience a 5 to 6 percent increase in gas mileage. Pretty good numbers in my opinion. The new gearing makes 4th gear a "tweener", it's now somewhere between where 4th and 5th used to be. I think it's great for freeway passing. When you're cruising at 65, and want a bit of power to pass, downshifting to 4th brings it, but without as high a jump in rpm as before. I think the only place that the small bit of power loss is noticeable is in 5th gear roll-ons. Except for that, I ike everything about the counter sprocket change. For thlose of you who care about such things, the engine is turning 5500 rpm @ 90 mph and 6200 rpm @ 100 mph. :-)

PARTS Chain -- I purchased a Tsubaki Omega 525X110. Not by choice, since I don't know one chain from another, that's just what they sent me.

Rear Sprocket -- Sunstar H01-MW3-670R--once again, not my choice.

16 tooth counter-sprocket -- The one I used was made by Sprocket Specialists, p/ n-594-16. I am sure that others make them too.

cotter pin -- You should never re-use cotter pins, so you will have to replace the one that goes on the brake stopper arm pivot bolt.

TOOLS Ratchet & Sockets -- I'm sure you all have metric sockets, but I will list them anyway. Make sure you have a:
24mm--rear axle nut
19mm--rear (driven) sprocket nuts
14mm--counter sprocket bolt
12mm--brake stopper arm nut

Other tools:
Torque wrench -- you really should have two if you're going to do your own maintenance. One that does around 10-90 ft./ lbs. for the big jobs, and one that goes from around 25 to 200 inch pounds, for the smaller stuff. The math is the same now as it was in the 4th grade: 1 ft./ b. = 12 in./ b.
8mm open or box wrench -- gear shift spindle joint bolt
12 & 14mm open or box wrench -- chain slack adjuster and lock nuts
17mm or adjustable wrench -- rear axle shaft
5mm x 3/ 8 drive hex bit -- drive sprocket cover bolt (I was unable to remove these bolts with a 5mm allen wrench. Maybe you can!
breaker bar -- believe me, unless you're a real gorilla, you will need at east a 12" breaker bar on the end of your ratchet when you remove the rear sprocket bolts. I actually used a 24" pipe. 72 foot/ pounds is a tough torque to break!
small c-clamp -- I found that this worked great for pressing in a tough master link.
channel locks -- worked great for sliding in the master link clip. Much better than needle-nose, in my opinion.

THE ACTUAL JOB: At times I will refer to the Owners manual and will abbreviate. Example: For page 15, step 8, I will refer to OM15-8.

Look over all of the steps before starting. You may not need to perform every single item. If your chain and sprockets are in good condition, and you just want to change the counter sprocket, you may be able to get enough slack to pull the chain off the counter sprocket by loosening the chain slack adjusters and axle bolt, then pushing the wheel all the way forward. There may be other variations, I didn't try them all. I was just happy to complete it successfully, without screwing too many things up! Remember -You can earn a lot from a "Wrench Dummy" !

  1. Run your bike for a few minutes to warm up the oil.

  2. Put the bike up on the centerstand-don't even try to do this job without a center stand or a bike lift.

  3. Drain your engine oil-Yuup, you have to drain it. (As I and others have observed, draining the oil is NOT necessary to perform this procedure--kru) You will be pulling off the left side change cover cap later, and you don't want oil spilling, nor do you want crud falling in. Yes, you are going to be amazed at the crud! Use a clean container if you are going to re-use it (the oil, not the crud). I was due for an oil change anyway.

  4. Loosen the rear axle nut-you may as well remove the nut and the "drive chain adjuster" at this point, since you will soon be pulling out the axle shaft. What is a "drive chain adjuster"? Well, that's what Honda calls it. It is the piece of metal that looks almost ike a retaining clip that sits between your axle nut and the right side swing arm (see figure in OM86).

  5. Loosen the chain adjuster lock nuts, then the adjuster nuts -This is necessary because not only is the new chain tighter (it's not stretched), but the 16 tooth counter sprocket is a larger diameter than a 15 tooth. I turned in my adjuster nuts 10 revolutions initially, but it turned out later that they needed to go in even more, so do 15 complete revolutions on each side. Do your best to keep it equal so you don't have wheel alignment problems when you're finished.

  6. Remove the rear brake adjusting nut (OM86-2)-the easiest way is to push in a bit on the brake arm, then unscrew the nut.

  7. Disconnect the rear brake rod from the from the brake arm-the OM recommends you depress the rear brake pedal. Since your sitting behind your bike at this point, you can also just push the rod with your hand. Either way works.

  8. Put the rear brake adjuster nut back on the rod so you don't lose it, the brake rod joint piece (which comes out of the brake arm), or the spring.

  9. OM86-3 -Disconnect the brake stopper arm from the brake panel (the panel which covers the right side of the rear brake drum assembly) by removing the cotter pin, stopper arm nut, the washer and rubber grommet-I recommend you put it all back in order on the stopper arm for temporary safe-keeping, and even draw a little picture, so you get the order correct when you reassemble later.

  10. Pull out the axle shaft-I sat behind the rear tire and worked the shaft out with my left hand, while supporting the rear tire with my foot underneath. It does make it easier, and it helps a little if you jiggle the tire/ wheel a little if the shaft hangs up. There is a spacer on each side of the wheel which will probably drop to the ground when you remove the shaft. If you forget where they go (I did, good thing I have a service manual), the shorter one goes on the left side.

  11. Push the rear wheel forward, then take the chain off the rear sprocket.

  12. Remove the rear wheel-careful here, the rear brake panel will be loose, as it is only held firmly in place when the wheel is tightly pinched between the rear swingarms.

  13. Look where the rear wheel used to be--OH MY GOD!! Look at all that dirt, and especially all that chain wax buildup everywhere!! Aren't you going to have fun cleaning all that! Actually, it's a perfect opportunity. You will also find wax buildup on your center stand, inside the chain guide, all over the back of the evaporation canister (if you have a California model), and splattered pretty much all over the rear wheel area.

  14. OPTIONAL -Pull the brake panel from the wheel-Since I was taking my wheel in to have a new tire mounted, I pulled this. They don't need it, and you don't want to have it damaged by a tire shop gorilla! This is also a good opportunity to vacuum (not blow) all the brake shoe dust out of the brake drum, and from the shoe area. Once it's clean, put a bit of grease on the rear brake cam (it's between the two shoes, and it moves when you move the brake arm. Caution: Do not get grease or oil on the inner drum surface or the shoes.

  15. OPTIONAL -Take the wheel in to get your new tire mounted-You might wonder why I didn't pull the sprocket off yet. I think it's better to eave it on. Having it on the wheel protects the studs/ bolts. And, if the tire tech was going to screw up a sprocket (not likely), I would prefer he screw up the old one.

  16. OPTIONAL -When you get the wheel back with your nice new tire, it's time to change rear sprockets-Of course, if your rear sprocket is still looking new, leave it on. But if you pull it, beware. It takes a lot of muscle (or a long breaker bar) to break the torque on thlose 5 bolts. When you put the new rear sprocket on, torque the bolts to 72 foot pounds. I hope you ate your Wheaties this morning. Set the wheel aside for now.

  17. Put the transmission in first gear -you will need to have the resistance of the engine compression when you loosen the counter sprocket bolt. If the transmission is in neutral, it just spins.

  18. Remove the gearshift spindle joint bolt-pull it all the way out. If left in, it will interfere when you reassemble (trust me on this).

  19. Slide the gearshift spindle joint off the spindle-you might have to wiggle it a bit, but it will come off. Do you see the punch marks? One on the spindle and one on the spindle joint? They need to be aligned when you reassemble later.

  20. Remove the black plastic change cover cap -you will put this back on in a few minutes. Also, be careful you don't lose the rubber O-ring.

  21. Remove the 3 bolts from the drive sprocket cover plate-this is the small round plate about 2 inches in diameter. These 3 bolts are the longest of the 6 that will be pulled. Make a little diagram, since there are 3 different lengths of cover bolts.

  22. Remove the 3 bolts from the drive sprocket cover-when you reassemble, the shortest bolt goes in the left ower front. The other two go in the right side top and blottom.

  23. Pull off the drive sprocket cover-this is easier than it sounds. You have to really maneuver it around to pull it. It may appear that the side stand switch connector needs to be pulled, but it doesn't, so eave it alone. OH MY GOD!! LOOK AT ALL THE CRUD AND CHAIN WAX BUILDUP!!! Calm down. Don't start cleaning yet.

  24. There are two shiny metal dowel pins (hollow cylinders) which may have fallen out when you removed the drive sprocket cover. ook on the floor (or driveway). If they didn't fall out, ook for them. One is above the sprocket and one below the sprocket towards the right. Make sure they get put back in when you reassemble.

  25. Remove the drive chain guide-it's a flat piece that's kind of U shaped. A few of the drive sprocket cover bolts pass through it.

  26. Put the black plastic cap back in place-you don't want the crud and old wax falling into your crankcase!

  27. Take the chain off the counter sprocket-just move it out of the way. If you plan on replacing it, now is a good time to take the old chain completely out. If it has a master link, just pull the clip, pull out the link, then remove the chain. If it is endless (the original Honda chain is), then it's a bit harder. You can buy a chain cutter, to cut out the link, or you can drill out the rivets. Or, you can grind them out. I used a dremel tool with a little cutting disc. After grinding the rivets flush (wear gloves and eye prlotection, the sparks fly), just pry a bit with a screwdriver and the link will pop right out.

  28. Remove the counter sprocket bolt, then remove the sprocket-you might as well save the sprocket if it's in good shape. You never know when you might need a spare. Besides, if you decide to return your bike to it's original condition later, you will need it.

  29. Clean-Clean-Clean-there's lot's of wax buildup everywhere. Just gently scrape it out with a screwdriver, then use a little bit of carb cleaner, or something similar, with a rag. It doesn't have to be splotless. As soon as you start riding again you're goingwantto be flinging wax or oil around again, but you do wan't to remove grime and keep the buildup down as much as possible.

  30. Install the new 16 tooth counter-sprocket-I put a little bit of grease on the gearshift spindle first. It may not be necessary, but why not? If you look at the counter sprocket carefully, you will notice that the raised portion is thicker on one side. The thicker side is installed towards the transmission, the thinner side towards you. Thanks to Honda of Milpitas for this bit of free advice! The bolt (14mm) gets torqued to 29 ft./ b.

  31. Temporarily put the shift linkage back on the spline, just enough so you can shift back into neutral, then take it back off again.

  32. Put a piece of clean newspaper or cardboard under the bike rear section so your new chain doesn't get dirty.

  33. Put the chain on the counter-sprocket-if it's the old chain, just put it back on. If it's a new chain, put it on and make sure you have one end above and one end under the swing arm assembly. I found it easier to put the master link in on the ower portion of the chain, and I did it after the rear wheel was reinstalled.

  34. Put the drive chain guide and the two dowel pins back in place.

  35. Reinstall the drive sprocket cover and the smaller drive sprocket cover plate.

  36. Torque the drive sprocket cover bolts (6) to 3.5 ft./ bs.

  37. Reinstall the gear shift spindle joint onto the spindle -don't put the bolt in until the joint is in place otherwise it will interfere. Insure that the punch marks ine up. You don't have to push the spindle joint way back against the case. Once a little bit of the spindle sticks out, that's far enough. Torque the gear shift spindle joint bolt to 10 ft./ bs. If you experience difficulty shifting out of neutral (I did), don't panic. Once the bike is all back together, just roll it back and forth a little and it will be fine.

  38. Clean, then put a light layer of grease on the axle shaft-clean the two spacers also, while you're at it.

  39. Reinstall the rear brake assembly into the wheel-just put it in, positioning isn't important.

  40. Get the axle shaft, axle nut, 2 spacers, and the "drive chain adjuster" near you, then sitting at the rear of the bike, roll that new tire into place as far forward as it will go.

  41. At this point, I put the chain on the rear sprocket, although it can be done later after the axle is in place-when installing the master link, make sure you use the rubber O-rings. It's pretty obvious where they go. If you experience difficulty pushing the plate in far enough to allow the clip to slide into the little grooves, I found that a small c-clamp worked great! Even better than pliers, in my opinion. I also found that a pair of channel locks worked much better than needlenose pliers for sliding the clip into place. Try it. You'll be impressed.

  42. Time for the rear axle shaft-basically , you're going to insert the axle shaft through the swing arm , spacer, wheel, spacer, then out the right side swing arm. Make sure the drive chain adjuster assemblies are positioned properly inside the swing arm. If they are upside down, you won't be able to see the adjustment marks. Remember the shorter spacer goes between the left swingarm and the wheel. Passing the axle through will be easier if you use your foot to raise the tire up. You'll get it right eventually. Just don't be too forceful. Rely more on correct positioning than force, or you might damage the threads on the end of the axle shaft.

  43. Pheeew! The heavy work is all finished. Go take a ten minute break.

  44. The rest of this is a "piece of cake."

  45. Snug up the axle bolt-not too tight because you still need to adjust chain slack and rear wheel alignment.

  46. Grab that can of chain wax and wax your chain.

  47. Adjust your chain slack between 0.8" to 1.2" --as always, make sure the alignment marks are equal on bloth sides to insure the rear wheel is aligned properly.

  48. Don't forget to tighten the chain slack adjuster lock nuts.

  49. Torque the rear axle nut (65 ft./ bs) -You'll need to hold the shaft bolt head on the left side with a 17mm wrench or an adjustable.

  50. Reassemble the brake stopper arm to the brake panel-do you remember the order? I'm glad I drew a picture. Torque the nut to 16 ft./ bs.

  51. Put the brake rod joint piece back into the brake arm, then reinstall the brake rod.

  52. Adjust the brake rod for 1" of rear brake pedal play.

  53. PUT THE OIL BACK IN THE BIKE!!-Or add some new stuff, with a filter, if you're doing the change.

  54. I think you're finished. Go check it out. Ride carefully at first. When you get back, recheck your chain slack, and make sure the master link clip looks ike it's going to stay on. Next time, hit the highway, and enjoy the lower rpm's . Your 5th gear rpm's should be about 400 less now.

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