Its actually pretty simple. Let’s take a quick look at the workings of a motorcycle engine:
- You chuck in some fuel, which gets mixed with air.
- This gets inducted into the cylinder where your piston is turning around.
- The piston is attached to a shaft, which turns your wheel.
- Add to the drive shaft different combinations of turning (gear box) and you’re able to drive faster or slower with the same engine power.
What Happens in the Cyclinder
Simple enough! Now let’s take a look at the process in the cylinder. Basically there are two engine processes: a two stroke or a four stroke engine. This means it takes 2 or 4 turns to return to the beginning position of powering the motorcycle. As you can imagine, having only two strokes makes it possible to power the motorcycle much more regularly. However, a two stoke engine is more reactive and a bit more nervous to drive. A four stroke is a little more laid back to drive.
How it Works
As gas and air are sucked into the cylinder the piston comes around and squeezes this gas mixture together. At the most effective time the spark plug ignites the mixture, sending the piston back down. The force pushes the shaft around. Now multiply this process by a few cylinders and raise the rate at which it happens and you’ve got a powering engine driving your motorcycle down the road.
Motorcycle Engine Buying Tips & Checks
Selection
First off, when looking for a new engine it’s important to think about your riding style. Different engines deliver different results. Do you prefer ultra-fast acceleration or do you want to sustain super fast top speeds? Or do you value a smooth ride? These considerations will all affect your engine choice.
Power
Motorcycle engines are specifically created for individual purposes. You should keep this in mind when it comes time to buy one. How much power do you want your bike to have? If you want a higher torque motorcycle motor, you should choose a motorcycle engine with less cylinders. For a smoother ride you may prefer a V-Twin or 4+ cylinder.
Cylinders
You’ll get more torque with a 1 or 2 cylinder motorcycle engine, but these engines are usually louder and slower turning.
Comfort
A motorcycle that has more cc’s isn’t always a more comfortable ride. A motorcycle that has cc’s in the 1000s may be really good for general touring, but will not be the same as a lightweight 4 cyclinder 650cc sport bike. We can’t have it all, right?
Aftermarket
The aftermarket motorcycle engine market is huge. You can get engines ranging from capacities in excess of 200cu inch (3000cc), all the way down to 74cu inch for shovel and sportster engines. Do some research and you’re sure to determine just the right engine for your needs.
Rotary Two-Stroke
The advantage of a rotary two-stroke motorcycle engine is that intake timing is not dependent on the transfer and exhaust ports. This is because the intake port is on the side of the crankcase and is dependent on position and the duration of the valve cutaway.
Overhead Camshaft Four-Stroke
Chain driven are more widely used than head cams due to price, noise-factor, and a host of other reasons.
CC
Power output and size of the combustion chamber in a motorcycle engine are interrelated. The upper limit is about 18-hundred cubic centimeters (cc), while the lower limit is about 50 cc. Of course engines in the lower range are usually found on small motorcycles.
Cheap Deals
Make sure you know who built the engine, even if you are buying from a supplier. They should be able to tell you. Outward appearances can be deceiving and there’s no way to know if the engine is well-built or not. If the price is too low there’s probably a reason. The last thing you want is a broken down bike and the cost to replace the engine will surely be more than the savings on a cheap one.
Output
Make sure you know the engine’s power output. Normally 1BHP per cu inch for an Evo motor is generally about right. With tuning and the right add-ons you can get more, but be sure the right mix of mid range and top range power to suit your riding needs is present. A competent engine builder should be able to offer a range of engines to suit your requirements.
Custom Kits
Custom kits are a great way to go. You get a fully assembled motorcycle engine that is matched for your transmission, frame, etc., along with everything else you need to build your bike. You’ll be on the road in no time.