The First Run

Well I finally got it to run!!! I had some problems with the glow plugs, but 2 new glow plugs and a lot of effort finally got things going. After a lot of trying, I finally figured out that the glow plugs were being quenched with oil after the engine stopped. This made it very difficult to get it started again. I turned the engine upside down and all of the problems dissapeared. The glow plugs are on a slight angle up. This allowed oil to pool inside of the glow plug, and would prevent it from lighting up. With the engine inverted, the oil will run out of the glow plug and it will light up normally.

The carb is an old carb from an OS 40-FP. An engine that I mostly destroyed while learning to fly R/C planes years ago. The carb seems to work pretty good. I really don't know if it is good or bad at this point. If it is bad, that means this engine will work even better with a good one.

The engine will turn a 18x6 prop 5400 rpm max. This is really not much for an engine this size, but it is better than I expected! I don't have any other props available so I don't know if the engine is loaded down of if it is at it's maximum speed. It will idle at well under 2000 rpm, but it will not run without the glow plugs being lit. I think raising the compression ratio will help this.

I went over all of the numbers for the engine and here is what "I think" that the engine is working with: (being the make-shift machinist that I am)
Bore : 1.100
Stroke : 0.968
Combustion Chamber Length : 0.190
Comb. Chamb. Area : .18056 C.I.
This gives it 0.92 C.I per cylinder, 1.84 total. This should give it a compression ratio of 6.09:1 That is not much compared to the typical glow engines with compression ratios of about 10:1. I plan to cut down the cylinders enough to raise the compression ratio to 9:1. That should give it more power and I hope it will allow it to run without glow plug current.

I also think the valve timing could be a little better. I have never verified the actual cam timing, but with just looking at it, it seems to be a little different from what it is supposed to be. I hope to verify the actual valve timing soon. If it is not at least what it is supposed to be, I am going to make a new cam. It seems to me that the valves should be open for a longer duration.

One thing that I noticed when running the engine was the temperature of the engine. It did not get hot! It was cool enough that you could hold it with your hand for 3 or 4 seconds. The typical engine would fry your hand if you held it that long! This is another thing that I think is related to the compression ratio. I think that raising the compression ratio will make the temp. increase. I could be wrong.

The numbers above are my own calculations, if I have mis-calculated, somebody please let me know.