I ran the Davis head a long time ago; it was a nice engine and put out enough power to fly an 09 powered RC sport plane (a Sig Colt), if marginally.

A couple of years ago I hauled it out and put it on an engine that turned out to be unreliable for other reasons; I could never keep the needle valve setting consistent -- and I burned through all my little teflon disks in one day's worth of cussin' and flippin'.

That's the only one I've got experience with: it's dead reliable on a good engine, but if you have a seriously lean run it'll burn the teflon disk just like high-nitro fuel with a glow plug.

Which engine are you planning to convert?  I found that the Tee Dee cranks are too weak, and fracture across the port opening.  The reed engines with the Davis crankshaft are a delight.  I suspect that the Medallion would work well too.  I have not tried a Norvel or AP Wasp.

I prefer the MECOA head because the teflon disks burn out long before the engine can be damaged (other than those Tee Dees wich did die using the Davis head).

There is a lot going for using an engine designed to be a diesel.  Rugged is their middle name!

Joking apart, I shall be interested to see if a converted Cox 0.49 can fly something like a Vic Smeed Tomboy. That can be flown on the old Amco .87 diesel or the Mills 0.75. I don't mind flying freeflight if junior does the retrieval!

I think a Cox 0.49 reed valve glow engine would be too big for a Nobler, much less something designed for 1/2A

(Somewhere out there on the web there's a set of pictures from a guy who really built a giant Cox reed valve engine, and it looks like it might be a 0.49 -- but I couldn't find it just now).

Andrew,
I am always befuddled by your use of the decimal point.  You refer to a ".049" as a "0.49".
That would make it larger than a Super Tigre .46!   Is there something I am missing in the translation?

Thanks, Buddy!
Bill

Hi Guys,
Sorry about the decimal point moving! I always have to think, because us Brit oldies always use cc for small engines and I always need to think twice when I am talking about small capacity American glows. It is odd but now we Brits use cubic inches for larger glows these days and it is only in the last few year that PAW have now started to refer to their small diesels in cubic inch terms. Sometimes you just get it wrong! We are half converted to the metric system and now going back to Imperial when it comes to toy engines............. Just to make you smile, our conversion to metric in the building trade means that a standard board is now 2400mm x 1200mm, a bit of an odd size until you realise that it is virtually a 8ft x 4ft board, same as it was in Imperial!

Glad I made you all smile at my expense!

Andrew.

Hi Bill,
I am way ahead of you on this one. I already have 3 PAW .55 diesels and like you say they are very good indeed. I also have a selection of the older style PAW 80s and 100s. I will come clean with you. I am teaching small grandson to fly a little free flight and as soon as he gets the hang of it, grandpa will retreat and let him learn by mistake if necessary. I don't mind losing a Cox 0.049, because they are cheap enough, but I am blowed if I am going to lose any of my hoard of PAW small diesels, like you say, they don't come cheap!
Oh and the diesel conversion is because us Brits have to smell correctly and diesel is the favoured aftershave of some of us old uns. In reality it is just so convenient to have a small valve spout full of diesel fuel and no hassle with batteries. Just helps small boys!
  I am not as mean as I sound. I managed to buy a pair of Doonside Mills engines from Steve Helmick......thanks again  Steve!.......Once junior is up and running and gets a taste for aeromodelling, he gets the Mills as a present.......so I am not so bad after all!

Regards,

Andrew.

Minor nit-picking?

The DDD conversion heads are from Bob Davis, not someone named Davies... Bob D has offered the teflon disk heads for Cox 1/2A engines for over 30 years... Sells excellent fuel, too.

Another conversion head is available from RJL, in California. Theirs is an O-ring sealed contra-piston type, and comes with a locking-bar for the comp screw.

As it fits the Cox glow-head threads, I tried the RJL head on a few NorVel (aluminum fin, not ceramic) .049 and .061 engines. A bit trickier starting than the teflon DDD heads, but they don't burn through. As I recall, I could turn a 5.5-3 over 18,000 RPM before I chickened out about the settings... (My own home-blend: 30E, ~41K, 22Oil, 1 or 2% DII.)