Engine basics > Engine set up tips
Diesel Conversion
rob biddle:
Hi all, I know that most will want know why would I bother, but I'm seriously considering converting an old FP .40 to diesel operation with a "Davis diesel" head.
I love to try out new things for the sake of doing it, whether it be good or bad it just seems to be food for my withering brain **)
The reasoning is that a diesel .40 will swing a 12x6 prop up to around 9000rpm and I figure that it should pull over 650 sq".
I have quizzed a couple of diesel fanatics on this and they haven't had any experience with the Davis conversion and couldn't offer much in the way of advice other than to run a very small venturi and apparently abc diesels aren't particularly successful. (not stating why?)
They both stated that the PAW .40 is very strong and will happily pull a .60 size model. Unfortunately the PAW is listed at 120 quid which equates to $301 Aud and is therefore beyond me for the present time.
I would probably be looking at a 4 stroke if spending this much.
The Davis conversion works out to be around $70 Aud which is more in my league.
On the Davis website the reviews look good but I don't know of anyone who has used this conversion first hand.
Has anyone on the forum used large diesels with success? I would love to hear the pro's and cons.
Thanks in advance, Rob.
Jim Thomerson:
The RJL 40 head is much cheaper than the Davis head. I ran one a good bit on a Tower 40 and liked the results. However, I did have a couple of problems. First, the contrapiston came apart. It has groove for an O-ring and the groove was close enough to the face of the contrapiston that the whole lower rim of the ring came off while the engine was running. Not good. Secondly, I went through four crankshafts. The shaft has a grinding relief groove around the shaft at the base of the crank web. Broke right across there. I was running a 2 oz heavy hub and I think that was a contributing factor.
If I build something which is not tail heavy I may try it again. Right now I have the head ( new contrapiston we made) on a magnum Pro 40 which has more substantial crank. Have only run it a couple of times on the bench.
I'm running the same venturi on the Tower 40 diesel or glow, muffler pressure. Have flown the Tower 40 several hundred flights glow with no problem, heavy hub and all.
Larry Wong:
Rob I have tryed a Davis diesel conversion on a O S 46 on and R/C plane,
I found that it works like a 4 stroke and has a lot of torque power, does not like to run like a 2 stroke ( high R P M ) run it rich and a smaller venturie with a throttle about 3/4 's throttle and it will turn a bigger prop. I had a tail pipe that came out the end of the plane, it seams to like back pressure also.
I hope this will help you. Good luck
rob biddle:
Thanks gents, I think that this may be worth having ago at if nothing else. ;D
It may be a little while off yet as my lovely wife has laid down the law and won't let me buy any more stunt goodies until I build the kits (x3) that I have accumulated over the last few months. n1
I guess she wouldn't know if I started on another scratch build as she was banned from my shed last time she complained about the 3 unfinished models and 2 half finished car projects. **)
I plan on building a 650+ sq" model with a "sidewinder" engine to allow better access to the compression vernier. It would have interchangeable "clamp" style mounts and tank access to facilitate an engine swap should the diesel conversion turn out to be a flop. :-[
Thanks again, Rob.
Ralph Wenzel (d):
Did you get my PM?
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