Archive for category d. Valve fabrication

Valve fabrication

As reed valves have been decided upon for this application, selection and sizing was first faced. While common on small displacement, low performance motors, reed valves for larger motors are less common. Available options were evaluated based on their physical dimension and the horsepower and displacement of the motors they were removed from. Polaris runs a particular design of reed valve on many of their larger motors that are of appropriate availability and sizing. The specific valves used were from 600cc Polaris personal watercraft. Figure D1 shows the reed valve relative to the size of the motor.

Figure D1: Reed valve mocked up on exhaust port

Housings were designed for these valves using the Rhino3D surface modeling software. Figure D2 shows the original valve housing design in a Rhino3D screenshot.

Figure D2: Rhino 3D screenshot of original valve design.

This original design called for a tapered profile in an attempt to minimize turbulence in the housing. Unfortunately, limitations of the milling machine required some design changes to allow for clearance and capabilities of the cutting tooling.

The final model was converted into orthogonal views and brought into the Cut2D 2.5 axis CAM software. Figure D3 shows a screenshot of the valve housing being processed through CAM software.

Figure D3: Valve housing model in Cut2D

Toolpaths for the CNC mill were created in Cut2D, then processed and saved in G-code for output to the mill controller.

The Tormach 1100 CNC mill was used for the fabrication of the valve housings.

Figure D4: Tormach 1100 CNC mill

4” x 4” x 3” billets of 6061 aluminum were used for the raw material. Billets were faced and then machined from the top and bottom in separate stages.

Figure D5: Facing the billets on the mill

Figure D6: Billet after facing

Figure D7: Machining top profile

Figure D8: Housing after top machining operation

Figure D9: Finished valve housing with nested valve

Figure D10: Finished valve housings mounted to cylinder head

Shows a brief video of the valve fabrication process from billet to housing.

In addition to the design for housings of the reed valves, the stock poppet valves needed to be removed from the cylinder head. Simple removal would not suffice, as the valve journals that normally house the stock poppet valves would be left open, making compression impossible.

Figure D11: Motorcycle head cutaway

Figure D11 shows a cutaway of an overhead cam motorcycle motor. The poppet valves are clearly visible, along with the path for ventilation that would occur with only their removal. A seal was created, using a bolt of proper diameter, o rings for both sides of the valve journal, appropriately sized washers, and a nylon lock nut. After removal of the stock valves, this replacement valve rod was put in place, the motor reassembled and prepared for testing.

Figure D12: Cylinder head with valves removed; valve journals visible

Figure D13: Bolt and o ring seal for valve journal

Figure D14: Journal seal in place

Figure D15: Motor reassembled, ready for testing

To verify proof of concept, one must revisit the earlier mentioned equations for mass air flow rate relations.

Once again, for a motor with an intake cycle on every rotation of the crankshaft, the denominator of 120 changes to a value of 60. If one were to compare the mass flow rate of the two cylinders, this equation states that the mass flow rate of the compressor cylinder should be twice that of the untouched cylinder, given than density, displacement, and rpm must be constant. To verify that the motor does in fact intake air twice into the compressor cylinder for every intake stroke on the untouched cylinder, the motor must be ran. A 12V source was applied to the starter motor on the engine, turning it over at a constant speed. Through observation, the engine can be seen to actuate the reed valves on the compressor cylinder at twice the rate of the untouched cylinder.

This is how the motor behaves under that power source, showing the timed movement of the valves.


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