Basic Gearbox Problems Rare

Gearbox problems are very rare nowadays, but normally only affect first-to-second upshift. The reason for this is that gearbox ratios are not evenly spaced but are widest apart at the bottom and become closer at the top. As a result, the speed difference and the shift impact are greatest on the first-to-second upshift.

That's why quick shifters normally work better from third upwards. This engagement impact from first to second gear is also transmitted through the gear teeth and then through the gear itself to the shaft. You can imagine what forces act on these gears when you are playing rough with 200 horsepower at the rear wheel. To make the gearboxes last and survive the high tooth-to-tooth pressure, gear surfaces are hardened by a nitride coating.

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Remove Paint from Threads

All of us who work on motorcycles, we have all been there; the painter or powder-coater forget to mask a thread. Taps and dies are good on small threads but what about larger ones? What if you're already fitted key parts and access is limited? Fill the back of any holes or spaces with clean rag and add masking tape if necessary.

Apply paint stripper (even the modern weak stuff) cautiously with an artist's brush then walk away for 30 minutes. Carefully dig into the threads with a pick, old tooth brush or similar to loosen the finish and vacuum off everything that loosens.

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Why Replace the Stock Front Forks

Almost all suspension feels good on smooth surfaces, but only some carries on feeling good over bumps.

Designing damper pistons that flow fluid inside forks and shocks, and the shim stacks to control them, takes time and money. It also costs money to keep internal friction at bay. That's why a set of Ohlins superbike forks will cost so much more than OEM replacement. You're paying for the precision of the machining, the accuracy of the damper cartridge bore, and trick coatings on moving parts. That matters if you're trying to outbrake Valentino Rossiā€¦

But sometimes you wonder if suspension feel is also about company philosophy. For many years in the '90s and early 2000s a good amount of motorcycle manufacturers, just didn't appear to think good high-speed control was particularly important. And maybe for some customers it isn't.

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Adjusting Fork Oil Height

Front forks contain oil which creates damping. You can change the characteristics of the fork by changing the height of the oil inside. If you increase the oil height, then the fork will become slightly stiffer and more progressive. If you lower the height, then the fork becomes less progressive. All front forks have manufacturer's specifications when it comes to oil heights but we will try to tell how to adjust the height easily on a general front fork.

Firstly, you will need to remove the fork from the motorcycle. On some forks, it is possible to adjust the oil height with the fork still on the motorcycle but, for the most accurate measurement, remove it from the motorcycle.

Undo the top fork cap and slide the outer fork tube down so you can reach the spring. Take a spanner, place it between the coils and hold the locknut on the damper rod.

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Top-End Rebuild

Some specialized tools are needed if you really want to check all the engine component specifications.

Before we can cut the valve seats, the head needs to be cleaned, degreased and carbon deposits removed. The header pipe gasket will be pushed into the head and locked in with carbon. You might need a pick or similar to dislodge it. They are usually made of copper and are one-use only since they compress to make a good seal. A new gasket should be in the top-end rebuild gasket kit.

When the header pipe was removed the nut locked onto the stud, causing it to wind out of the head. Now is a good time to fix it back in place. Use high-strength Loctite as the low or medium type is broken down too easily with heat. Wind on two nuts to the stud and lock them together. This will allow you to tighten the stud into the head. Two spanners are then used to unlock the nuts so they can be removed from the stud.

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Compression and Cam Timing

Increasing compression will likely gain horsepower, though there are multiple ways to go about approaching this. The easiest way to add compression is to deck the block or go with a thin head gasket, both ultimately reducing the squish band (the outer portion of the combustion chamber where the piston comes closest to the cylinder head). But a thinner head gasket isn't always an option, and a lot of times, we do prefer to cut the block so that if we lose a customer – if he moves across the country or something – and he has somebody service his motorcycle, that person could just put a stock part back in his motorcycle and not have a problem.

Of course, every engine builder is going to have their opinion on what squish number is best, and for a supersport class engine you'd want to run it on the safe side. For me, I know the customer is going to be running this for a year or so before it's inspected again, so I wouldn't run the squish number as tight as I would for a engine that's going to get rebuild after a few race weekends. You can take material off the cylinder head, though the effect can be less due to the shape of the combustion chamber. Taking material off of the cylinder head will also affect cam timing, as will a thinner head gasket.

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Engine Rebuild and Tuning

Horsepower is an addictive thing. And while not a replacement for sheer riding ability, it will at some point in your riding career play a role in both going faster and having more fun at the racetrack. How do you go about getting more of it, assuming you've already made the more straightforward modifications like an exhaust system, fuel controller, and/or re-flashed ECU?

For anyone who wants to take his trackday riding or racing to the next level, the answer is an engine build. Of course, that's a broad answer, as the term 'engine build' can mean any number of things depending on who you talk to and what you as the rider want/need. Adding to the complexity of the situation is that, in most supersport-based builds, emphasis is not only placed on power gains but in assuring continued reliability. The reason for this is that, in racing (or even trackday riding), the internal parts turning fuel into power are put under great stress, and over time those components can wear down, so much that a refresh is necessary, regardless of how good the manufacturer's production pieces are.

We've reached out to a professional motorcycle tuner, who illustrates the important aspects of an engine build and removes some of the confusion surrounding the subject.

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The Cush Drive Delivering a Smooth Ride

There's a control system on your motorcycle that probably gets very little attention, yet it's an important contributor to ride quality. It's your motorcycle's cush-drive system, and its job is to smooth driveline lash when getting on and off the throttle, and so soften the power pulses transmitted to the rear wheel from the crankshaft.

When a piston pushes down on the connecting rod during the power stroke, it does so with a violent shock. The flywheel's mass smooths some of this shock, but if the remainder of the force generated by these power pulses goes unchecked, it can make your ride uncomfortable, as well as damage driveline components.

Cush drives use either rubber dampers or spring-loaded mechanisms to soften driveline shock. The most common type is the rubber cush drive and it's located within the enlarged portion of the rear wheel hub, behind the rear sprocket. In a motorcycle with a cush drive, the rear sprocket is bolted to a removeable carrier, which interlocks with rubber dampers inserted into the wheel. Power is transferred to the wheel through the rubber dampers, and it's the dampers' pliancy that absorbs the power-pulse shocks.

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How to install a thread insert

Thread repairs often come in for bad press yet there's little justification if you've bought a decent product and installed it correctly. Yes the job is effectively a quick fix to a bad situation but it should never be looked upon as a bodge. Well, not unless the person fitting the insert is a fool or a klutz.

The first and most serious crime against thread inserts has to be trying to do the job in situations without proper access. Drill an oval, off center or angled hole and ask yourself why the bolt or stud you subsequently fit either pulls out or doesn't line up. Wherever possible, take the damaged component off the motorcycle and work of a flat surface with the part to be repaired held down firmly and squarely.

In some instance this this just isn't feasible; cam caps within cylinder-heads, exhaust studs etc. in situations such as these it makes sense to fabricate a guide or pilot block that will ensure the dril enters the damaged thread true and perpendicular. With a block or scrap metal, a little ingenuity, the odd G-clamp, a spare pair of hands or even a tie wrap or ratchet strap it should be possible to get the drill positioned correctly.

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Why Select a Single or Multi-Cylinder Motorcycle

There’s only so much we can upsize with a single piston cylinder arrangement before hitting the mechanical upscaling effect that are, beyond a point, almost impossible to overcome. To get more power imagine doubling the cylinder stroke as well as piston diameter.

The resultant will be a 8 times increase in the engine volume, for same MEP the power output will be 4 times and torque 8 times but the weight of the piston, connecting rod and crank will also increase 8 times making previous high rpm’s from the simple single-cylinder engine impossible to achieve without breaking the crank or the connecting rods! All such complications apart, there’s what is called the ‘flywheel effect’ that also needs attention. In a 4 stroke cycle, it is only the power stroke that is producing power while the rest of the 3 strokes ride piggy back on it.

Going by this fact the piston comes down the fastest during the power stroke and will progressively slow down during the rest of the 3 strokes, the greatest slowing down occurring during the compression stroke.

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