56 Terrier Motorcycle

FRS 106, Michael Littman – Spring 2014

Top End

Otto Cycle Simulation

Without Cam drive and push rod

This is a simulation of the Otto cycle in a four stroke combustion engine.

We began by taking apart the head, which required disassembling the intake and exhaust valves and then taking inventory of the parts. Using a telescoping gauge and a micrometer, we took measurements of the bore and the shaft, according to the specifications from the Triumph Motorcycle Manual.  From these measurements, we found that a piston which was 60 thousandths of an inch larger than the specs which fit perfectly  inside of the bore to fit together to meet the specifications of the manual. Ideally, the space between the circumference of the piston head and the inside of the barrel is no greater than the thickness of three pieces of paper.

Meanwhile, Glen 3-D printed a rapid prototype of a throat to connect the carburetor to the head. We learned that the stoichiometric ratio of air to fuel necessary for combustion is 14.7:1.

We also used the ultrasonic parts cleaner to clean the intake and exhaust springs and washers. We then went on to measure the spring constant for each of these springs. We used the milling machine to compress the ring force gauge with the springs on top. From there, we increased the force in increments of five pounds, and measure the change in length for every increment. The calculated average spring constant, along with the rest of the data is in the table below.

Special thanks to Nigel for his insight and knowledge which helped us greatly in understanding the mechanics of the top end and engine as a whole!!

We recently completed sandblasting the head. From there we grinded the valves using a lathe and grinding wheel and recut the seats on the newly sandblasted head.

As you can see, the spring constant on the exhaust valve is slightly less than the intake valve.

The red line indicates that, if operated at a high speed, our exhaust valve would close slower than it should because of a lower spring constant than our intake valve spring. However, our motorcycle will not be operated at such a speed so it is unlikely to cause problems.

Final Presentation