The Little Engine That Could

I figure that since I started the month with a slice about a project that I was working on I should end the month with a project that I am working on.  As many of you know, I have been working on a 125 as my winter project.  I have all of the things done on the bodywork part of it and I now have the performance motor work finished, so it’s time to put the engine together.  Since a 125 is considered the baby of big motorcycles it's important to get as much power out of the engine as possible.  However, I refuse to cheat, so I gain performance by doing specialty work myself that is completely within the guidelines of the 125 class instead of sending a motor to have it built illegally like so many people do.    The performance work that I was doing was matching the cases and porting and polishing the cylinder.  It makes a big difference in the way a motorcycle runs, but is very expensive if you have to send it to someone to do it.  Fortunately, I know how to do it, so it only cost me some time.  The first thing that I do when doing this type of work is matching the cases. To do this, you have to take the engine completely apart so that you only have the engine covers and the cylinder.  This was not a problem since I needed to take the engine apart to repair it anyways.  Next, you bolt the cylinder onto one of the engine covers.  You then have to carefully grind away any of the metal that overlaps where the surfaces meet.  The purpose for doing this is to make the transitions as smooth as possible.  The fewer disturbances there are the better and more efficiently fuel and air can flow through, which creates more power.  Think of it as a vacuum cleaner that is partially plugged.  Yes, it still works but it is not nearly as efficient or powerful as it could be.  After the cases are matched it is time to work on the cylinder porting.  Ports are open spaces in the cylinder that help control fuel and air flow.  The more efficient the porting is the more powerful the engine is.  Porting is tricky, though, because a lot of people think that to port a cylinder they need to make the ports bigger so that you get more fuel and air.  This is not the case.  The cylinders and ports are designed by the manufacturers to certain specifications for a reason.  If you make them bigger, you mess with the timing and other critical features of the motor.  When I port a motor I am simply cleaning up casting flaws, (since the pieces are cast and not handmade there are some imperfections) smoothing transitions and sharpening dividers so that things flow better.  On the exhaust port (where everything finally leaves the cylinder) I used a polishing compound and polished everything to a mirror-like finish so that things flowed very well out of the cylinder.  You, however, should never polish the other ports of a cylinder because a polished surface will not allow the fuel to atomize correctly and will defeat the purpose of doing all of the porting work.  As I said before, it’s a tricky balance.  After spending hours of cleaning up the ports and matching the cases my engine is finally ready to go together!  Now I just have to assemble the complete engine and get it in the bike so that it’s ready to ride.  I can’t wait!  With spring break on the way I am hoping to be doing some assembly very soon.  When it's all finished I will post pictures.  I’m sorry about this slice being so long, but I figured that I should probably put some explanations as to why and how I was doing things to allow you to better understand.  There you have it, 31 days and 31 slices!