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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Check if Wheel Alignment is Correct

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.

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Extra Maintenance by Using Ethanol Fuel

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.

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WD-40 and your Motorcycle Chain

Whether or not WD-40 will keep your chain's O-rings happy or ruin them is one of the most controversial topics in motorcycle maintenance. Supporters say WD-40 is great for cleaning your chain and won't harm a thing. Critics say WD-40 – or more specifically the petroleum distillates in WD-40 – will dry our the O-rings, displace the grease, and ruin your chain.

What's the truth?

To begin, 'WD' stands for Water Displacement, and the '40' stands for the 40th formula to be mixed up. The safety sheet for WD-40 says that it's mostly Stoddard solvent, a petroleum product similar to kerosene. So for all intent and purposes, WD-40 is mostly kerosene. And most motorcycle owner manuals actually recommend using kerosene to wash your chain.

Okay, but WD-40 isn't 100 percent kerosene, and there might still be something in that secret formula that will cause your chain's O-rings to swell up and die. So, to find out just how damaging WD-40 might be we disassembled a motorcycle chain an dropped some O-rings into pure uncut WD-40 and let them stew for a week.

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The Honda MSX125 as 180cc Pocket Rocket

The Honda MSX125 is a very popular motorcycle in Thailand, one of our mechanics even bought one for home – work transport. The Honda MSX125 is equipped with the same engine you find in the Honda Wave 125i, and as you probably can imagine that engine is not known for high performance.

For Honda MSX125 owners you can buy a wide range of performance enhancing parts, which offer an even wider range of increased performance. Not so long ago we where contacted by Kitaco Japan, so we asked them what they had for solution to give the Honda MSX125 some extra grunt. The Japanese company responded with a 181cc big bore kit that included everything you need to upgrade the engine. The Kitaco 181cc big bore kit also included a oil cooler, Type 2 performance camshaft and a fueling modifier.

The Kitaco 181cc big bore cylinder is plain aluminum, and really stands out from the engine if fitted like that. We decided to spray-paint the cylinder with in the traditional black color. After we fitted all parts, we realized that the Kitaco 181cc big bore kit needed a much less restricted exhaust pipe. Luckily we where able to obtain a Ixil 615BB Full exhaust system from a local dealer for 4500 THB.

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Rebuilding Your Two-Stroke's Top-End

Rebuilding a two-stroke's top-end is a relatively cheap, easy and quick way to give your old two-stroke motorcycle a new lease of life. A worn piston and rings won't form a tight seal in the cylinder, which can scuff the bore and starve your engine of power. Fitting a new piston will protect your engine from expensive damage; if a weakened piston cracks after months of abuse can cause all sorts of strife.

During a top-end rebuild, your motorcycle's most highly stress components will be open to the elements, so ensure you clean your motorcycle thoroughly and completely dry it before taking it apart. Remove the fairing to open up some room so it is easy to get your tools in and then disconnect the fuel line from the carburetor. Remove the fuel tank and now you should have unobstructed access to the top end of the engine.

Remove the coolant if the motorcycle has liquid cooling by the drain bolt and empty the engine and radiators of all coolant. Once all the coolant is out of the radiators disconnect the radiator hoses from the engine and remove the spark plug. Remove the exhaust pipe mounts and remove the exhaust system.

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How many times have you crashed your motorcycle in the last three years?

  •  Never
  •  Once
  •  Twice
  •  Three times
  •  Four times
  •  Five times
  •  More than 6 times
  •  More than 10 times
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