Hello Everyone,

I have been lurking in this forum for a while now, and have just started to explorer diesel engines. I purchased a Davis conversion for a cox 049 reed valve engine, and have been testing it over the last couple days. So far, I really like what I see. I think this Diesel thing could catch on with me! I was wondering what props you could recommend for this setup? I really can't seem to find a lot of information in that respect. The only thing I can find is "start with one inch bigger than glow".

Thanks for your help
Chris

You can use propeller 5x3, 7x4 for 0.49 size engine.

Jens Eirik

Thanks Jens. Also, those little teflon discs that provide the seal, I keep blowing those. I have gone through all three of those I have in two runs. The head when tightened down, seems to cut into the teflon around the perimeter, and then the seal is ruined. The compression all leaks out from around the compression screw. How do you keep those damn things from getting cut by the head? I have even tried under-tightening it, and it still happens. I guess no more runs now till I can get some more teflon sheet from Small Parts inc.

Chris

The disc must be centered in the bore so you do not cut the edge are you using the aluminum disc over the teflon?? I have had blown a few but have it down now the system has worked welll for over 25 years martin
If you ae still having problems give Davis a ring monday 203-877-1670

dieseldan - the discs are centered in the bore. I am not using the aluminum discs, the instructions said they were only necessary for the norvel. May this be a good idea?

Chris

Chris,

Davis also has a strong crankshaft for the reed engines. Cox reedies tend to break crankshafts with a diesel conversion. Perhaps the newer Cox reed engines have a stronger crankshaft.

George

I spent some time messing about with Cox reedy diesels this summer.

I used the Davis head and the RJL head and had both work reasonably well. At the moment I prefer the RJL but I had no problems with Davis so I can't comment on the teflon disc issue. I did however use the aluminum disc as well.

As to props, I used Master Airscrew 7x3 and 7x4 although as Jen's mentioned you could go much smaller ( ie 5x3 or 5x4) or even up to an 8x3 or 8x4 - RPM will vary from prop size to prop size (naturally) as will compression and needle - bigger prop, lower compression.

I did learn quite impressively that you will break stock reedy crankshafts, if not sooner then later. I initally used a Cox car crankcase and crankshaft which are larger in diameter with a thicker crank web but I ended up breaking those too.

If you really want to keep you Cox reedy diesel together, spend the $15 for the Davis heavy duty crankshaft, it is beefy where you need it - the crank web.

Picture one shows my latest conversion - currently in a 1/2 playboy - turns a 7x4 at 11,000 using a TD piston cylinder set

Picture two shows shows the same engine but with the smaller tank and exhaust stub. The exhaust stub doesn't work well with sub port induction

Picture three shows the very first incarnation with the car crankcase and crankshaft but using the RJL glow head, I also ran it using the Davis and RJL diesel heads. I broke the crankshaft while running the Davis head.

Picture four shows the broken car engine crankshaft (compare the thickness of the crank web with one from a typical reed valve plane engine.

Good luck,

cheers, Graham in Embrun near Ottawa Canada

The Cox 7x3.5 would be fine, but I'd recommend a wooden 7x7 or 8/4 for less damage to your fingers. The connecting rod and crank pin will be a bit safer if the 7 and 8 inch props are used. Work with all the thrust available from the extra torque at lower speeds instead of going for higher RPMs with smaller diameters.

Davis has a deal the crank and the head for $25 I think the reed engine martin

Thankyou everyone. I have had it running pretty well now with a 7x4. I did order the reed valve 049 conversion that included the head and the crank, but Mr. Davis Diesel forgot to put the crank in the package before it was sent out, so I have been running it with the standard crank. The new crank is on the way.

Chris

Graham,

I really like your innovative, reedy engine mount for the test stand. Also, that's a neat looking little spinner. Where did you get that?

The test mount is not my idea. There was fellow selling these on Ebay, one side takes the typical 049 reed valve engine and the other side the ubiquitious product engine. I was going to make my own using his idea but I ended up buying one of the pre made ones and it is very well made. He told me he had them done on a CNC machine. He also had a size availabe to suit the Pee Wee. Now that I have my Taig lathe set up to mill I would just make one next time.

The spinner is a Mp Jet spinner that uses a tapered split collet to fit electric motors. I made up a new tapered prop driver to fit the Cox crankshaft over which the spinner plate then fits, made a prop nut threaded through to hold the prop on a 5-40 stud in the crank and 4-40 button head screw from the front of the spinner. The spinner is 30mm in diameter. I have set up a 3 engines like this so far and haven't had any problems. The spinners are inexpensive. I get them from Icare-RC www.icrare-rc.com - about $12.00 C$. He also has 40mm size. Etienne has very competitive prices and is great to deal with. He travels from time to time and is a one man shop but he usually updates his contact information on his web site with details when he is away.


cheers, Graham

Nice job on the spinner. I'll have to keep that in mind.

Thanks Graham,

That spinner is perfect for my little Spitfire. All I have to do is anodize it black. Neat.