Compression Stroke
During the compression stroke, the piston moves from BDC back to TDC. Since both valves are completely closed, the mixture is compressed tightly into the combustion chamber. Why does it need to be compressed? First, compressing the gas thoroughly mixes all those fuel and air molecules and raises their temperatures, making them easier to ignite. Secondly, a compressed mixture expands with greater force when ignited than one that isn't.
Power Stroke
The third one's the charm. With the piston at TDC and both valves closed, the spark plug is fired, igniting the mixture. As the mixture burns, the gases expand, pushing the piston downward, rotating the crankshaft and feeding power into the motorcycle's drivetrain
Exhaust Stroke
The final step is to remove the burnt gases. As the piston reaches the bottom of the power stroke, the cam opens the exhaust valve. The piston now starts to move back toward the top of the cylinder and, as it does so, forces the spent gases ahead of it out the open exhaust valve. As the piston reaches TDC, the exhaust valve closes, and the cylinder is ready to start another intake cycle.
Details
There you have it. Like too many things in life, engines appear mysterious to the uninitiated, when in fact they're pretty simple. Hopefully some of the mystery has now been replaced with understanding. If not, you've got my e-mail
Idiots Are Me...
When I make a mistake, it's a doozy, and there's a winner in the August Tech Tip "Recharge the Right Way." To reduce current flow, the load needs to be connected in parallel, not in series, as I stated. Sorry for the gaffe-I'll be studying remedial electrical theory over the summer.-MZ
Uplifting
Motorcycle Lifts 101Once found only in dealerships and available primarily through specialist suppliers at great expense, motorcycle table lifts have become both cheap and accessible, making them perfect accessories for do-it-yourselfers.
Before purchasing a lift, you'll need to consider a few basics. Obviously, space is one. Lifts average about seven feet in length, give or take a few inches, and you'll need at least a couple of feet in every direction just to swing your wrench. So make sure you've got the physical room before you place the order. Of course, you can always park the bike on the lift if space is tight.
Overhead clearance is another consideration, especially if your shop is in the basement. Typically, a lift will raise your bike somewhere around 30 inches, so add that to your bike's highest point when it's in the vertical position. I'd recommend at least two feet of clearance or you'll likely be picking parts out of the ceiling.
You'll also want to make certain the lift can support the weight of your bike. Although most table lifts are capable of handling a 1,000 pounds or so, some are rated at considerably less. It probably won't be an issue if you're tinkering around on a typical midsize cruiser but could present a problem if you're a Boss Hoss or Amazona enthusiast.
Types
Power sources vary: Air- and electrically operated lifts are the most popular, with foot-operated hydraulics bringing up the rear. In-ground automotive-style lifts tend to be difficult to install and expensive, and as such, unsuited for home use. I prefer the electric lifts: They're less troublesome to use, don't need a compressor and use a screw-type lifting mechanism, which permits a fine height adjustment and also prevents the lift from dropping in the event you don't have the safety stands down during a mechanical failure. On the downside, they tend to be a bit more expensive and operate more slowly. My second choice would be the air-operated version. My last choice is reserved for the foot-pumped hydraulic style.
If you opt for the air- or hydraulic-type lift, make sure there's some sort of drop-down locking system just in case things go really wrong with the lifting mechanism.