During the first practice at a track a rider will ride around and determine brake markers, shift and turn-in points, safe passing zones, potential hazards, and which way the track goes past any blind rises.

After deciding on a basic pattern for a lap and picking up speed, the next step is to refine the picture by adjusting gearing choices. The two things you’ll need to consider for determining the proper gearing are mid-corner rpm and straightaway rpm. Your drive out of corners depends on your ability to keep the engine on the boil at the top part of the rev range. On a typical inline 4-cylinder 600cc racebike it is best to keep the engine above 9000 rpm as much as possible. However, you also want to avoid running out of acceleration by hitting the rev-limiter on the main straightaway as well as on any short chutes between turns. Sometimes you have to compromise between drive out of a corner or two, the speed attained on the chutes and the speed on the front straight. If we were running GP bikes we would then swap internal ratios to pick the perfect say, third-gear ratio but we race production 600s which only leaves us with swapping final drive ratios. Choosing final-drive ratios can be further complicated by planning for faster lap times and the effect that running in other bikes’ draft might play on gearing.

We gear the bike for acceleration out of key corners that help the most with lap times and still allow for acceleration on a straight. Usually a faster corner leading onto a straightaway is better to optimize than a slow second-gear corner exit. Determining which way to go with gearing can be tricky if you rely solely on a rider’s impressions and input, since this can be influenced by traffic in practice, a bad lap, any number of things. This is where a datalogger can be helpful to capture lap times, speed, and front wheel speed. The data does not lie, and we can decipher the data traces to come up with an accurate look at the track layout and rpm range in each corner and on the straights, and use that to guide gearing choices.

Generally the stock gearing is heavy and too tall. We swap out the stock steel rear sprockets for aluminum ones in 520 pitch, the stock front sprocket for a steel 520 pitch, and the chain for a 520 O-ring type. The chain we use is one of the more expensive ones, but you get what you pay for. It lasts a whole four weekends of endurance racing without complaint, and then right on cue it stretches like taffy. It also has a master link with a mandatory press-fit side plate and expanding rivets. You can still buy chains with clip-type master links but we avoid these because the clip could jettison after only a lap.

We carry a crate full of 44, 45, and 46-tooth rear sprockets, and 14, 15 and 16-tooth front sprockets. This selection fits a GSX-R600 well enough. A Yamaha YZF-R6 uses 47, 48, and 49-tooth rears. They are both 600s revving to similar-ish rpm, but the internal transmission ratios are different enough to require different sets of sprockets. We’ve used AFAM, Renthal and Vortex but we had pretty much come around to just using Sprocket Specialist at about the time they decided to sponsor us, which was a very happy coincidence.

Typically moving one tooth on the front equals about a 1000-rpm change in sixth gear. Swapping from a 15-tooth front to a 16-tooth front will bring the revs from 15,000 rpm to 14,000 rpm at a given speed or, if horsepower, wind resistance, track length and rider disposition are all favorable, allow the motorcycle to attain a higher speed at the same 15,000 rpm. Rear sprockets are about 300 rpm per tooth and go the other way. A 46-tooth rear will bring the rpm up to 15,000 compared to 14,700 with a 45-tooth rear. Shorter gearing (smaller fronts and larger rears) makes the bike accelerate faster, taller gearing (larger fronts and smaller rears) gives the bike a faster top speed. With the sprockets we carry we can go from a short of 14/46 to a tall of 16/44 (gear ratios from 3.29:1 to 2.75:1) on the GSX-R or 14/49 to 16/47 (gear ratios from 3.50:1 to 2.94:1) on the Yamaha. We have yet to find a track outside of those extremes. We can also fit all of that gearing with a stock length chain.

Chain and Master Link Installation:

It used to be that most chains were held together with a convenient hand-assembled clip-type master link. At least it was convenient until the clip came off after a few laps, setting the chain free to break the water pump, clutch pushrod and anything else in its way. Fortunately those days are behind us, and chains that require massive force and determination to even install are available. Following is a pictorial about cutting a chain to length, and properly assembling a rivet masterlink. Installing a chain is one of those activities best left for a time when there are few distractions. Make peace with the world and yourself, and begin.

With the rear wheel about midway through its travel in the swingarm slots, wrap the chain around the sprockets to gauge how long the chain needs to be. This 120-link chain needs to be shortened to 110 links. Count the number of links you want to take off. Count again. Maybe again. Mark the rivet. Make sure you will be left with a link that a masterlink can go into. Never end a sentence in a preposition, up with which we shall not put.

New chains come with the rivets staked or peened over so they won’t fall out. To push one out with a rivet remover you should grind the offending rivet flush to not strain the rivet removing tool. The machine that peens all those rivets must be quite a thing.

After grinding, you end up with something that looks like this.

Use a rivet press to drive the rivet out.

The chain will be hooked together with a rivet-type master link. The ends of the rivets are expanded over a press-fit side plate making for a safe solution. Proper assembly is important, of course, as we learned one year at a 24-hour race when an improperly installed rivet link flung free from its chain. The resulting crack! (as the chain whipped up to bend the subframe before wrapping itself in a tight curl around the countershaft sprocket, breaking all the sprocket cover mounts off the case in the process), was enough to stop the hearts of the pit crew standing at hot pit lane. Not to mention the rider, who was thankful the subframe was there to stop the chain from hitting something more vulnerable, like his leg or foot.

Don’t let this happen to you!

Thread the chain over the front and rear sprockets on the motorcycle, and get the master link ready by rounding up the o-rings and gacking them up with lube.

Hook the chain together with the master link.

Put the remaining two o-rings on the master link rivets and start the side plate on as best you can with your fingers.

Partially press the plate on by squeezing the plate onto the rivets with pliers or Vise Grips. Alternate between ends to get the plate on evenly. Eventually the rivets will be flush with the side plate. Next find the tool to push the side plate on the rest of the way.

This RK rivet tool comes with two plates for pressing on chain side plates. One plate has a deeper groove and is designed for use with a clip-type master link. The other plate is for pressing the side plate onto a rivet-type master link. The rivets must be exposed enough to squash out so the side plate can’t come off.

Drive the sideplate on until the groove in the tool plate bottoms out on the heads of the rivets.

The link should still move freely.

Remove the tool and replace the plate with the conical rivet expander. Drive the nose of the expander into the indentation in the end of the master link rivet to spread it out such that the sideplate can’t come off.

Measure the outside diameter before and after forcing the expander into the rivet. Usually about 0.4mm of change will ensure that the rivet has expanded sufficiently to keep the side plate from coming off. If you try to expand it any more than that you can crack the end of the rivet, and would you trust a chain with a cracked rivet for six solid hours at over 100 horsepower?

One down, one to go.

Front Sprocket Install

Beware the output shaft locknut. If the bike doesn’t come with something like this Yamaha output shaft lock washer we recommend adding one. This stock YZ-R 6 part also fits the GSX-Rs.

If your class rules allow, and you’re running a GSX-R, it is quite handy to cut out the front sprocket cover so you can change sprockets without having to remove and replace the cover. Put the sprocket on the output shaft with the chain threaded over it, and the rear wheel and sprocket loosely installed. Put on the nut and lock washer. Tightening the nut with a torque wrench is nerve-wracking, as it is difficult to keep the rear wheel from rotating without jamming something in the spokes. We usually end up just zapping the nut on with an airgun and hope for the best. Take up the slack in the chain by putting your foot on top of the chain when you whack the nut on with the airgun. Otherwise the airgun just makes the chain bounce up and down and less force goes into tightening. Bend the lock washer against the nut as shown above. GSX-Rs use a Hall effect speedometer sensor. Use the piece that bolts onto the end of the output shaft and covers the countershaft sprocket nut as an extra safeguard.

Chain Adjustment

Ideally, the rear wheel should be parallel to the front wheel. Use a caliper to measure from the back of the chain adjuster block that the axle goes through to the back of the swingarm, which we feel is better than just eyeballing the adjustment against the stock swingarm lines.

Make sure that there is enough slack in the chain. Most manuals recommend 25-35mm of chain slack, measured at the mid point of the chain, under the swingarm. We usually err towards the higher end of the slack scale. If your chain is not new, rotate the rear wheel through the full range of the chain and set the slack at the tightest point on the chain. If you have too much range from tight spot to loose spot on the chain, it’s usually due to one of two reasons: 1) the chain is worn unevenly and should be replaced, or 2) the rear sprocket is not concentric (i.e. the center hole is not in the center) and should be replaced.

After setting the static chain slack, make sure there is some slack while there is a rider sitting on the bike.

Electrical Modifications

Switches, switches, switches. We are terribly superstitious about any sort of switch that has the potential to kill the motor. The street safety interlocks can cause great wailing and gnashing of teeth while trying to figure out why the bike stopped working for no good reason other than to remind us that we have gray hair and steely nerves after all these years for a reason. We bypass the clutch lockout switch, the sidestand switch, and disable the tip-over switch. The first two are mostly a matter of convenience, although removing and bypassing them eliminates the possibility of a faulty switch rearing its ugly head sometime. The tip-over switch is another matter. The idea is that if the bike falls over, the ignition and fuel pump are disabled so the bike is not running on its side and either oil-starves itself or feeds fuel to a potential fire. This seems prudent until your bike hits a bump or slides while leaned way over and the engine dies and your rider, who has not raced four-strokes much, starts to push the bike back into the pits while your three-lap lead is slowly dwindling away and reducing the chance that you will take your first-ever overall endurance race win.

The Suzuki tip-over switch is a marvel of engineering. The metal donut in the center jiggles its way along the plastic armature as the bike is leaned over in some flat-out 4th-gear kink until it completes a circuit and kills the engine. As the bike won’t run without the switch, the workaround is to fill the housing with gasket goo, and put the cover back on.

We replace the ignition switch with a toggle switch (a Yamaha WR headlight switch is a good choice) because they get pretty crunchy inside after a while. You have to put a 100 ohm resistor in the circuit to replace the stock ignition on a Suzuki. If you use the stock ignition switch, be sure to safety wire the key into the ignition so it doesn’t end up permanently missing if you crash.

Those groovy drag race "dead man" switches were cool for a little while. These had a pin in the ignition attached by a springy cord to the rider. If the rider were flung off in a crash, the engine would stop, presumably saving the engine. But they are too unreliable, particularly for endurance racing.

Soldering

To become a certifiable assembly technician for the Apollo Moon flights, you had to go to school for a month to learn how to solder. The first week was spent just learning how to strip the insulation off wires without nicking the conductor. A nick in the wire is a weak spot which could eventually break from vibration. The more you know about a subject, the more reasons there are to lie awake nights fretting, which is the reason AOD will never build and race airplanes. But sooner or later you have to turn off the contrived reality/makeover shows, get off the couch, grit your teeth, and pick up the soldering iron.

Strip the end of the wire with the appropriate stripper.

Tin the tip of the iron by melting on a bit of solder. Use some sort of rosin-core solder from Geek Shack— between 0.040-0.050-inch diameter is a good size. Incidentally 0.040-inch solder is good for measuring the piston-to-head clearance, usually.

Wipe the tip clean with a damp paper towel or a sponge just before you intend to solder a connection. The tip should appear shiny. If there is a bunch of burned-on schmutz, scrub it off with some sandpaper or a wire brush and tin the tip again.

Spread the individual wire fibers on both wires into a fan shape and insert one fan into the other, then twist them together. If done correctly you should have a hard time pulling the wires apart even without the solder.

Heat the conductors, and feed solder into the crux of the iron’s tip and the conductors. The solder will flow out into the connections. If the tip is tinned properly and everything goes just right the solder will flow just after instantly, without heating the wires enough to melt the insulation just next to the joint.

Army of Darkness tipover switch test rider Ben Walters cranks it over en route to an overall endurance win at Jennings GP. Photo by Louis Gagne.

Tim lays out the tools of the trade as he prepares to practice his chain-changing craft at the track. After carefully following the chain installation procedure outlined in this article Tim realized he had just changed the chain on the “B” bike instead of the “A” bike, which had the worn out chain on it. Photo by AOD MOI.