propjobbill

I bought a diesel head conversion from RJL for Cox .049. I have not been able to get it running steady yet. Has anyone used one of these conversions, and are they worth the trouble? Do they really give more power?

vauxhall

Hi Propjob,I don't know about Cox diesel conversions,but,I do know diesels,been using 'em since the early sixties,and I love 'em.The first thing you need is FRESH fuel.The ether in diesel fuel seems to evaporate through steel cans,and the fuel should have a good shot of amyl nitrate in it.I guess you know the compression screw needs to be turned in or out to get smooth running and max power,and your needle valve setup as well. The comp. settings may vary from one day to the next,depending on temp. or fuel etc.What is your specific problem?Starting,power or something else?I would recommend a visit to the P.A.W. website,lots of info for diesel operators.Maybe you should have a look at their 049 diesel,they're a top little donk.I hope another member has experience of the Cox diesel conversion and can help you out,but,tell what the exact problem is.

DesignMan

Let's back up a step. What fuel and prop are you running. Often people buy diesel conversion heads, then get diesel fuel at the gas station. That DOES NOT WORK!!! Model diesel fuel is a unique mix, as mentioned above, with Nitrates and Ether in it. Lots of ether.

My favorite is Aerodyne fuel, followed by Red Max. Davis fuels work just fine, but the exhaust seems to come out a lot darker than the others. Doesn't seem to actually hurt anything, just ugly!

propjobbill

Thanks for the comment, I am using the Davidson diesel fuel for 1/2A. I put a small prime in the exhaust port it will fire on the second time I wind it up (it has a spring start) but it runs for about 1 half second until the prime is gone and then dies. I have tried dozens of times but I have never got it to run. I sure wish I could figure out how to keep it running. I have tried turning the needle valve in and out. I have starved it of fuel and gave it so much it flooded but I can't get it to stay running.
No one around here runs diesels that I know, and no one sells the diesel fuel. I know if I can get it to run I will like it. Most everyone that writes about diesels love them. They say you get more power from Diesels.

Any help will be appreciated

combatpigg

My Feedback: (3)

HI PROPJOBBILL! I wouldn't dieselize a COX, they aren't built for it. A NORVEL or AP 061 is built a little bit better, but they are marginal too. I have only tried starting mine with electric starters, a real diesel guru could probably hand flip one, but I think the tiny bore engines don't create a good enough preheat through compression to make hand starting as easy as glow. If your compression is close to right, as soon as fuel reaches the carb from continuous cranking, it should fire up. Look for air bubbles coming out the head. You want to hear burbling from under compression as soon as it fires up, the less time you spend accidentally overcompressed, the better. Creep up slowly on compression until you clean up the sound, then work the needle, look at the exhaust spray. A tach is handy for tuning these, once you get to know the engine/prop combo. A 7-3 is basically the only practical prop to use, because you don't want to over power load the rod and crank pin. You can turn a 7-4, but your best thrust should be with the 7-3 APC.

propjobbill

Hi Combat, I got it running today with a 7-3 Airmaster prop it runs at 11,000 and that is on a reed engine. I could probable get more out of it, but with the reed engine i Don't want to push it. You are very knowledgeable and very helpful my
Sincere THANKS

combatpigg

My Feedback: (3)

HI PROPJOB! Good going! I wondered what a reed would give you, a good .061 will hit 13500 with an APC 7-3. To give you an idea as to how much more torque you are putting on the crankshaft, a 6-3 at 13000rpm[typical reed output] has a load factor of 3888 and a 7-3 at 11000 has a load factor of 7203. The 6-3 would give 9.5ozs of thrust and the 7-3 would be giving 12.8ozs of thrust, plus lots of foul diesel odor all over the place!