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David Kerzel, Pompano Beach, Florida david@FloridaAME.org
Hit and Miss Number 1, 1 Cylinder, 4 cycle, 0.75 bore X 0.80 stroke
I started designing this engine on January 13, 2001. It is based on several different designs in Strictly IC magazine, Bob Shores Little Angel, and several actual hit and miss engines I saw at Pioneer Days in 2001. The design started with drawings for the main part of the engine and as those parts were made the smaller details added. I worked on it actively for several months, lost interest, and now am finishing it up.
The engine is made of bar stock. The gears and springs are shop made.
During the long gap my ideas about engines have changed and my workmanship has improved. Several weeks ago I thought I was done and ready to start it. The valves leaked, and the points were not reliable. I remade the valves and guides using a silver soldered design, made new points. In the next few days I will get the ignition on and working, then it just needs starting. Once it runs there are a lot of little details to go. 9/6/2002
Notes, problems and details
This is the valve test block (fixture) I used to verify my valves were actually leak free. See the Valve Spring thread in the message board under Construction questions. I kept lapping the valves until I could no longer hear any leakage when compressed air was applied to the test block. This is a good method or determining that the valves do not leak for single cylinder engines. An adapter to insert compressed air into the sparkplug hole is a better plan for multi cylinder engines. 9/29/2002
My second carburetor designed with the jet in the elbow and an integral check valve for the fluid. At times liquid comes out of the exhaust, but I am not sure if it is fuel or condensate. The engine fires but will not yet sustain operation.
A third carburetor was made that has a spray bar design. It seems to work the best, but all will be tested again when the engine finally starts and runs for a full tank of fuel.
This is a test plate made of Lexan to verify that the spark plug fires after the compression cycle. As pressure increases so does the voltage required to start an arc. I pressurize the fixture to 75 PSI and trigger the points. I get a fat bright spark every time.
I Made still another test plate when it still would not start and found a leak so large I could feel it leak between the piston and the cylinder on my finger. The parts were lapped and had a diameter difference of 0.0003 but no rings. When I made the piston I saved material lapped to the correct size for rings when the engine wore out in years. I used the method described in early issues of SIC. I started with a counterbore in one end of the fixture to hold the slices of ring material for sanding on #400 wet/dry silicon carbide paper to get the exact thickness at 6 points. I made the heat treating fixture that springs the ring open while the heat treatment sets the new shape. I cut the rings with end nippers and loaded then on the fixture. I cleaned everything and started to heat it. When it is about 450F I dip it in anti-scale powder that melts over the surface and keeps the parts from getting black scale (most times). Continue heating till dull red, and wait 1 minute, then let cool slowly in air till cold. Soak in warm water for about 30 minutes to dissolve the anti-scale. Two strokes on each side of the gap with #400 to clean up the gap, and check in the cylinder for 0.001 gap and its done.
Now I have compression. There is so much compression it is difficult to try to start. But it does start and run for about 5 minutes. I think rings are still the issue because when it stops the compression is low again.
Finally after nearly 23 months my engine starts and runs. Click here for a video.
For the past 3 weeks it would start but not continue to run. I kept checking things. Common sense said something was heating and adding friction. Then I noticed water droplets on the spark plug insulator. I wiped it off and it started and ran until more drops formed. My 3 part plug was leaking and shorting out the plug on the out side.
Now I need to test the various carburetors and other items that came and went during the various trouble shooting cycles.
Then the final fit. polish, and paint.
1/5/2003 Many problems came up during early testing over the holidays.
First, when testing with Regular Gasoline the engine stopped running and was full of black carbon dust. I had originally been using Methanol for fuel. The fist test was to try other liquid fuels. I posted a thread in the message board about the problem and several people said too much oil in the cylinder was the problem or I was using the wrong oil. I had been keeping the hole for the oiler filled with #30 motor oil during the tests.
I started by not adding any oil, but the cylinder went dry and the engine stopped in about 15 minutes. I added a drop of oil and it loosened up. By disabling the speed regulator and checking the RPM I could see when the cylinder was getting dry and adding a drop of oil would increase the speed several hundred RPM in a second or two. I used 3-in-1 and #20 non detergent synthetic turbine oil. Both worked well and did not foul the cylinder and only produced the slightest amount of black deposits that just wiped off. I added oil at the rate of 1 drop every 10 minutes.
I got a digital tachometer from David Bowes http://rbowes1.11net.com/dbowes. It uses a hall sensor and a magnet to measure speed. My magnet is held on a flywheel with blue tape and I had not finished the box for the tach yet. It is good unit for testing because it displays the minimum, maximum and current speed. Later I will embed a rare earth magnet in a brass holder for future testing.
When I started testing the engine did not run as well as it had before and appeared to be getting weaker. The timing gear on the crank shaft had slipped and the spark was happening 45 degrees after TDC. Fixed that and got the highest speeds I have ever seen and go more than one miss per hit for the first time.
Copyright 2003, Florida Association of Model Engineers and engine builder as noted above, All rights reserved.