maggyneo

Hi Guys, This is my first post in this forum. Pardon me if this is not the right forum to shoot this question. I am a computer science grad who is very passionate about bikes and cars. I was wondering if there would be some automobile gurus on this forum from either Hyderabad or Chennai, India who would be ready to personally walk me & a couple of my friends(we can decide the place based on your convenience) through the engine mechanism of bikes or cars perhaps during their past time. It would otherwise be helpful if you could provide me with pointers on some good videos and references(websites, ebooks etc.) to look up to understand the engine mechanism.
I am a novice as far as the technicality of bikes are concerned even though I was owning a normal bike like pulsar as well as a superbike Suzuki GSXR 750. The level of detail I am looking at is as follows:
1) Initially a high level detail of the difference among normal bikes(pulsar), superbikes and cruisers/Bullet.
2) References/videos to details on how each of these machines work( if they are very different)

With the good insights provided by the engineers on this forum, I am sure I should be able to dissemble and reassemble a basic bike and if a problem occurs, if the mechanic tells me some technical issue, I should be able to validate it.

Maggy

Noor

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I'm not in either of those places, but I've been messing around with engines my whole life, so I'll try to offer what I can.

I will assume that you understand the basics i.e. how the piston and crankshaft translate the force of the burning fuel into mechanical energy.

The main differences in engine architecture between "ordinary" bikes, high-horsepower superbikes, and "cruisers" are the bore/stroke ratio and the compression ratio, and the number of intake/exhaust valves. They all work basically the same otherwise. The differences are merely matters of degree (two-stroke bikes *do* operate differently; let me know if you want to know more about them). They will all have a multiplate clutch, usually "wet" i.e. submerged in oil (usually the same oil used by the engine and transmission), and a sequential manual transmission (you can only shift to the next higher or lower gear).

An internal combustion engine, at its heart, is essentially an air pump. The more efficient you make the pump i.e. the more air you can get it to move, the more power it produces.

Ordinary bikes will have a moderate compression ratio, probably around 9:1, an "undersquare" bore/stroke, which means the length of the stroke of the piston is longer than the diameter of the cylinder, and one intake and one exhaust valve in the cylinder. The valve timing (when the intake and exhaust open and close during the rotations of the crankshaft) will be set to provide the most efficient operation at low to medium RPMs, and will try to balance horsepower and torque fairly evenly.

Superbikes have much higher compression, possibly as high as 12:1, will have "square" or more commonly now "oversquare" bores, so that the piston doesn't have to move as fast in its cylinder to travel the distance of the stroke. These bikes will generally have two intake and two exhaust valves, though some bikes had three intake and two exhaust. The valves will be timed to be more efficient at higher RPMs, and will heavily favor horsepower (to keep the bike moving at high speeds) over torque.

Cruisers tend to have slightly higher compression than ordinary bikes, which allows for a greater focus on torque than the ordinary bike. The engines tend to be undersquare, with long strokes at the expense of being less-suited to high-speed operation (again, this favors torque). Valve timing will favor low-rpm operation and again be set to produce torque rather than horsepower (less valve overlap).

Valve timing is used to adjust an engine's performance through the degree of "overlap" i.e. the amount of time that the exhaust valve remains open when the intake starts to open. The less overlap, the more torque the engine will produce, and the less horsepower. The longer the intake is open, the more air/fuel can get in, but there is some loss of compression.

There are any number of wikipedia articles that will provide more in-depth information on engine operation; you can start here:
Engine tuning - Wikipedia, the free encyclopedia

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