Has anyone tryed this yet? I'm thinking it would make an easy contra piston. It is good to 500* F. Also I'm thinking it might have a good insulation effect thus keeping more heat in the compression process. It is possible that it will have heat issues.

Treven.

Could be worth a try-but the low coefficient of friction might mean getting the right interference fit for easy adjustment versus not working back near impossible. Also-if it does overheat-and melt/burn hydrogen fluoride will be one of the combustion products-very nasty stuff!
I assume you have a conventional style of contra in mind? A push-pull type would be more work-but probably more practical, though I'm not sure how teflon would handle the loads on the thread imposed by the adjustment screw

'ffkiwi' (wondering why no one has tried it before.............or have they?)

I have a very vague recollection that Andy may have used PTFE or similar for a contra piston before. That same recollection has me thinking that it didn't work out to well in the end.

I can't recall the details and couldn't find the post after a quick look. Perhaps when Andy is on again he will see this thread and comment.

cheers, Graham in Embrun near Ottawa

Davis includes teflon disks with their Cox conversion heads. The contra doesn't do the sealing in this case. I have yet to try one, but some people say they burn up every run.

500F seems like a lot but the burning gases will exceed that.

Greg the teflon disc will blow out if engine engine too hot or overcompressed think of is a "fuse" it wil save the engine remember he also makes the strong crankshaft for this engine at 25$ for the crank and head it is a good deal RJl head 20$ ( no crank)
and yes they do have to be replaced after some runs not much more of a deal than changing a glow plug when set up right they do last for a number of runs ditto on te norvels it saves the rod, radical departure from his other heads but has worked well for over 25 years I do have the cox 020 new and the same set up which has not been run yet martin

Why is a part that needs to be replaced every few runs acceptable? I thought the reduced maintenance was an attribute of diesel. I have a few Davis .049 heads. I haven't used them yet. I did use an RJL head many years ago, and still have it. I never broke the crank in my Black Widow, but it didn't get a whole lot of time on it before I went to larger engines that weren't so messy.

It might burn but I have to say Teflon is not easy to burn. Try it. The Buna N 0 rings seem to put up with the temps ok but I guess the aluminum contra protects them some.

Yes, I tried an all Teflon CP. It worked great for a few minutes then the engine started to go rough. So I turned in the CP and got my power back. Then it sagged again and so on. In the end, my CP screw bottomed out.

The Teflon CP had a very clean, neat hole burned into it. The hole was biased toward the exhaust port indicating that the incoming fuel charge was cooling that side of combustion chamber.

Yes, Teflon can withstand a common butane torch all day. It just goes clear on you and sags a bit. BUT, it burns in our engines. Too bad,, good idea.

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This thread shows me how far behind the curve I am. I was under the impression that all of the Davis heads used PTFE technology.

Sorry your about 35 years to late we patented our diesel disc back in 1975. The reason it works is the mass of a thin teflon disc is very little and what the disc sees is the average temperture between the cold fuel mist and the hot fire. The disc last as long as you fly the engine as this is a much lesser heat load then a bench. We were the first people to put a plastic inside of a combustion zone of as engine. Those that burn out the disc are those that bench run at fuel power and over heat the system. also if you don't clean out the old varnish deposits from castor oil from the glow runs you insulate the cylinder and don't let the heat out thus blowing a hole in the disc. when the Norel came along customers put our heads on the 061's with great results however the power shortened the life of the discs so we added a thin aluminum disc first then the teflon behined them and that works for quite awhile. A Norel .061 an a 6 X 4 turns between 18,500 and 19,500 Rpm and thats a bunch.

What brand the 6 X 4 ?

Grish, their black plastic with white tips. The difference was between two Norvel .061's, so much for precision on the part of the Russian engine makers. If that was a Cox TD 500 Rpm would be more like a difference.

If the prop was a Grish, then that IS pretty impressive. And about Russian precision. I've been dealing with Norvel from the very beginning and consistently, they have, year to year, improved and expanded their products. Yes, they have had some glitches along the way.

But they have virtually aerospace technology built into their engines. Nickle plated pistons along with hard anodized cylinders. Instead of a hard/soft combination, they give you a near diamond hard/extremely hard combination. A vast improvement over ABC technology even, which itself is over 40 years old.

I love all my Cox engines, despite the design being what, 60 years old? They all still have a very modern, appealing look. But looks is where it ends. Cox technology is just as old. Yet today, you pay MORE for a TD than you do for a Norvel. What does a stock TD do on diesel, on a 7 X 4 ? And what is Cox doing today, despite having the world's largest market right at their back door?

Here, http://www.youtube.com/watch?v=o-uvAb-vQgM you can see a TD .09 with good power to weight and pretty darn good throttling. This one is rigged up with an MVVS .09 throttle with adjustable airbleed. The muffler is custom made. It competes very well with the Norvel .074 but it DOES have more displacement. I'd dieselize it but I'm afraid to break the crank.

Here, http://www.youtube.com/watch?v=PRn5i6Knisw is a dieselized, Norvel .06 doing 4K to 10.4K on a COX 8 X 4 prop with perfect throttling. Perfect. An adjustable airbleed has been installed on the carb and the crankcase has been altered to take a proper, bolt on muffler. We are also using muffler pressure to the tank. And the crank has taken the extra loads that diesel and this size prop imposes with absolutely no problems.

I've dieselized the entire range of Norvel engines. The .06 and .074 have been flown extensively. The .15 has had dozens and dozens of bench runs on all manner of fuels including those made up of acetone, mineral spirits and even WD 40.

ALL of the Norvels have had starters applied to them with utter abandon. The ONLY problem was bent rods. And that only happened when I got careless. In ALL cases, the cranks have stood up to the beating.

Am I a fan of Norvel? How can you tell?

The last time we tested TD's we ran Cox 7 X 3.5 and they turned 13,000 Rpm. There are no more Norel .049 or .061's there history. By the way they were AME's the Norel was an American Import name. As for all that market the electric motor coupled with Li-poly killed that although it was on its way out when Airhogs took over the department strore market and forced Cox on the ropes were Estes bought them to use in the Star Wars program which failed leaving Estes in trouble, remeber after Estes bought Cox they stoped advertizing them period. Norvel was in the market at the perfect time and lets not forget that Estes sold off Most of the machines that made Cox engines leaving them at the mercy of outside shops thus the line was cut down to nothing and the prices went through the roof. Although there is a hobby market for a limited amount of .020's no one has yet to produce anything to compare with the TD .020 or the .010 Bill Atwood was the genius. The first piston and cylinger set used in the .049 Cox came from K&B .049 parts sold to Leroy Cox By John Brodbeck of K&B.

Hello Bob.,

It's good that you consider that there is a market for an 020.
There's a business opportunity for you!

I have made and have available, an excellent 020 diesel.
I have designed and may make, a modern, high-performance 020 glow.

But, we both know that any good engine must fetch at very least, half a weeks wages to be a viable proposition.
They did then and probably do so now.
If manufactured in our countries, that cost would limit even that limited hobby market.

Peter