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Cox Engine of The Month
September-2020
sosam117's

"Traded an electric charger for this "Complete" (original) Cox Thimble Drome Olympic .15 engine. Right corner is photo as received."



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Post  Ken Cook on Sat Jun 13, 2020 8:47 pm

I made several attempts at using diesel conversions on a Cox babe Bee. Early attempts failed me due to crank pin and shaft breaking. Over the past few weeks, I took out my diesel heads to give it a go. First up was the Davis Diesel heads with the Teflon discs. I had a heck of a time with these. However, I've made terrific runs and flights with them. Lose the head gasket in your engine. This is what I believe was proving to be most problematic for me. Just use the disc. My plan is to use the engine in a free flight plane but I was really familiarizing myself with it's characteristics today. I have to say I'm glad I didn't give up on this. I melted two discs which wasn't quite the same as blowing them out due to over compression.

In order to get the plane maneuverable, I had to lean the engine up but also backing off the compression as much as I could to maintain smooth higher rpm's. While my flights were not as fast as glow, I was using a Master Airscrew 6x3.5 prop, this was giving good drive but not a lot of speed. However, it looked terrific going through at a nice steady pace especially the wingovers. It really left me with a sense of accomplishment as I've tried this before and my success wasn't like today.

I also tried the RJL Mecoa head, this particular head wasn't as gratifying as the Davis head. The RJL seems to offer easier starting but maintaining steady rpm's wasn't as easy. The RJL head also didn't offer the performance I was getting with the Davis setup. I'll admit, I'm not a big fan of those Teflon discs but they do work. I have some shim stock to try and substitute it for the Teflon. All in all, I was proud to say I got some very successful flights. Ken

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Post  Mike1484 on Sun Jun 14, 2020 9:18 am

Hi Ken ,

I have used the Teflon disks in an .09 Tee Dee for Control line and a friend used it for free flight . I have also made and used Teflon in my own heads . I can say that I'm not a big fan of the Teflon disks but they can and do work O. K. . I also have used the Davis conversion heads with the aluminum contra piston / O-ring and they work very well on the larger displacement motors like O.S. and Super Tigre's . I have hade good luck making my own conversion heads and they work good also . I always wanted to try backing up the Teflon with a thin copper or brass shim stock disk . Some people have made aluminum disks and have had some good results . My thoughts on small diesels is the best ones have a lapped steel or cast iron contra piston directly inserted in the cylinder , and the O-ring heads are second inline as are the Teflon disks . Watch those crankshafts on the Cox engines , I've snapped a few crank pins on the .020's and .049's . Use the diesel cranks
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Post  robot797 on Sun Jun 14, 2020 12:08 pm

I never had a teflon disk break on me
but I started using aluminium (cheaper)
they break easy but they run better
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Post  Ken Cook on Sun Jun 14, 2020 6:13 pm

Mike, I did break the crank in my engine twice when I tried this before. I switched to the Davis Diesel crank and all has been good. In regards to Davis Diesel conversion heads, I never realized how well they actually work. I have probably 2 dozen of them for various engines from the .049 to the Super Tiger 3000. One that I'm really impressed with is the Fox .15 BB, what a terrific running engine on diesel. Another is the K&B .61 head this works absolutely sweet.
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