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 Rossi…
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.
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.
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.
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.
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.
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.
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.
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.
We have to say that it's more an issue on older motorcycles, a quick check of a few less traveled models showed that those wee markings on the swingarm adjuster aren't necessarily gospel. In fact, some of them are downright liars.
With a quick check, you may find your wheel alignment is correct, as was the case with the last motorcycle we checked. If not, the old way still works if you don't happen to have any lasers in your toolbox. If your motorcycle feels better carving left than heading right, or the otherway around, it may just be this simple. Be aware though: if you've purchased a used motorcycle and the frame and/or swingarm is bent, it will really stand out.
Although technically the stringline will be accurate if under enough tension, make it easy for your self and use a well-swept concrete floor. Right, after that you ideally need a race stand to give a clear line for the string to go through. You'll also need a couple of relatively heavy objects to hold tension on the string. Axle stands or fuel containers – full, obviously – are fine if you have some around.
If ethanol fuel has been stagnating in your fuel system for more than two or three months, an ultrasonic cleaning bath won't always clear that glue-like gunge from the jets and airways. This is particularly true if the carburetor are not stripped and are just dunked in a tank as an assembly.
You often need an old-fashioned approach, and that means going to someone with the knowledge and confidence to go inside the carburetor, stripping out every component and individually cleaning them as well as all the drillings in the carburetor bodies themselves. Sometimes they'll need to use chemicals that could cause damage if used incorrectly.
We know about a person who recently bought a motorcycle that had been stood for a time. He spent a small fortune on replacement ignition components because he'd had the carburetors cleaned in an ultrasonic bath, so he ruled them out as the cause of his continuing running problems.